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Li R, Du Y, Zhou Y, Ouyang Z. Identification of HSP70 genes in Diaphorina citri Kuwayama Reveals Their Involvement in Immunity and Development. Mol Biotechnol 2024:10.1007/s12033-024-01232-4. [PMID: 38940979 DOI: 10.1007/s12033-024-01232-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2024] [Accepted: 06/13/2024] [Indexed: 06/29/2024]
Abstract
Huanglongbing (HLB), a global citrus threat, is transmitted by Diaphorina citri Kuwayama, a widespread insect pest. The disease's rapid spread and incurability necessitate efficient, sustainable control strategies. This study investigates heat shock protein 70 (HSP70) genes in D. citri, known to play a pivotal role in insect survival and stress response. The genome-wide identification, gene structure analysis, and conserved protein domain analysis of 22 HSP70 genes in D. citri were performed. Furthermore, the expression of these genes during HLB infection or developmental processes was gauged. Phylogenetic analysis revealed the functional categorization of the identified genes, while gene structure and conserved motifs offered insights into gene function. The expression analysis unveiled dynamic profiles in response to infection and across development stages, potentially aiding future targeted pest control strategies. These findings offer promising leads for the design of novel inhibitors or RNAi strategies targeting D. citri and HLB.
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Affiliation(s)
- Ruimin Li
- College of Life Sciences, Gannan Normal University, Ganzhou, 341000, China.
| | - Yimin Du
- College of Life Sciences, Gannan Normal University, Ganzhou, 341000, China
- National Navel Orange Engineering Research Center, Ganzhou, 341000, China
| | - Yan Zhou
- College of Life Sciences, Gannan Normal University, Ganzhou, 341000, China
| | - Zhigang Ouyang
- College of Life Sciences, Gannan Normal University, Ganzhou, 341000, China
- National Navel Orange Engineering Research Center, Ganzhou, 341000, China
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2
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Ameline A, Karkach A, Denoirjean T, Grondin M, Molinari F, Turpin P, Delatte H, Reynaud B. Bacterial plant pathogens affect the locomotor behavior of the insect vector: a case study of Citrus volkameriana-Triozae erytreae-Candidatus Liberibacter asiaticus system. INSECT SCIENCE 2024; 31:901-910. [PMID: 37822228 DOI: 10.1111/1744-7917.13279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2023] [Revised: 08/25/2023] [Accepted: 08/30/2023] [Indexed: 10/13/2023]
Abstract
Plant pathogens can alter the behavior of their insect vectors as well as their survival and reproduction. The African psyllid, Trioza erytreae, is one of the vectors of Huanglongbing, a citrus disease caused mainly by "Candidatus Liberibacter asiaticus" (CLas). The purpose of this study was to characterize the effects of CLas on the psyllid, T. erytreae using Citrus volkamerina plants as the study system. The study focused more specifically on the CLas effects prior to and after its acquisition by the psyllid T. erytreae. Our results did not support the hypothesis that CLas effects psyllid probing behavior prior to acquisition; few differences were observed between uninfected T. erytrea feeding on CLas-infected versus control plants. On the other hand, compared to psyllids that had completed their development on control plants, the ones that had completed their development on a CLas-infected plant exhibited changes in their behavior (greater velocity), physiology (smaller mass) and biochemistry (lower water and lipid content). Altogether, our results confirm the existence of a marked postacquisition effect on the vector locomotor behavior and a minor preacquisition effect of CLas on the vector behavior, which can be partially explained by physiological and biochemical changes.
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Affiliation(s)
- Arnaud Ameline
- UMR CNRS 7058 EDYSAN (Écologie et Dynamique des Systèmes Anthropisés), Université de Picardie Jules Verne, Amiens, Cedex, France
| | - Alain Karkach
- UMR PVBMT (Peuplements végétaux et bioagresseurs en milieu tropical), Université de la Réunion, Saint Pierre, La Réunion, France
| | - Thomas Denoirjean
- UMR CNRS 7058 EDYSAN (Écologie et Dynamique des Systèmes Anthropisés), Université de Picardie Jules Verne, Amiens, Cedex, France
| | - Martial Grondin
- UMR PVBMT (Peuplements végétaux et bioagresseurs en milieu tropical), Université de la Réunion, Saint Pierre, La Réunion, France
| | - Florencia Molinari
- UMR PVBMT (Peuplements végétaux et bioagresseurs en milieu tropical), Université de la Réunion, Saint Pierre, La Réunion, France
| | - Patrick Turpin
- UMR PVBMT (Peuplements végétaux et bioagresseurs en milieu tropical), Université de la Réunion, Saint Pierre, La Réunion, France
| | - Hélène Delatte
- UMR PVBMT (Peuplements végétaux et bioagresseurs en milieu tropical), Université de la Réunion, Saint Pierre, La Réunion, France
| | - Bernard Reynaud
- UMR PVBMT (Peuplements végétaux et bioagresseurs en milieu tropical), Université de la Réunion, Saint Pierre, La Réunion, France
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3
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Bilal MS, Paul G, Yu Z, Xu L, Cheng T, Cheng B, Aslam MN, Baig A, Zhao H. Comparative Transcriptome and sRNAome Analysis Suggest Coordinated Citrus Immune Responses against Huanglongbing Disease. PLANTS (BASEL, SWITZERLAND) 2024; 13:1496. [PMID: 38891304 PMCID: PMC11175137 DOI: 10.3390/plants13111496] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2024] [Revised: 04/24/2024] [Accepted: 05/02/2024] [Indexed: 06/21/2024]
Abstract
Citrus Huanglongbing (HLB), caused by the phloem-inhibiting bacterium Candidatus Liberibacter asiaticus (CLas), is the most devastating citrus disease, intimidating citrus production worldwide. Although commercially cultivated citrus cultivars are vulnerable to CLas infection, HLB-tolerant attributes have, however, been observed in certain citrus varieties, suggesting a possible pathway for identifying innate defense regulators that mitigate HLB. By adopting transcriptome and small RNAome analysis, the current study compares the responses of HLB-tolerant lemon (Citrus limon L.) with HLB-susceptible Shatangju mandarin (Citrus reticulata Blanco cv. Shatangju) against CLas infection. Transcriptome analysis revealed significant differences in gene expression between lemon and Shatangju. A total of 1751 and 3076 significantly differentially expressed genes were identified in Shatangju and lemon, respectively. Specifically, CLas infected lemon tissues demonstrated higher expressions of genes involved in antioxidant enzyme activity, protein phosphorylation, carbohydrate, cell wall, and lipid metabolism than Shatangju. Wet-lab experiments further validated these findings, demonstrating increased antioxidant enzyme activity in lemon: APX (35%), SOD (30%), and CAT (64%) than Shatangju. Conversely, Shatangju plants exhibited higher levels of oxidative stress markers like H2O2 (44.5%) and MDA content (65.2%), alongside pronounced ion leakage (11.85%), than lemon. Moreover, microscopic investigations revealed that CLas infected Shatangju phloem exhibits significantly more starch and callose accumulation than lemon. Furthermore, comparative sRNA profiles revealed the potential defensive regulators for HLB tolerance. In Shatangju, increased expression of csi-miR166 suppresses the expression of disease-resistant proteins, leading to inadequate defense against CLas. Conversely, reduced expression of csi-miR166 in lemon plants enables them to combat HLB by activating disease-resistance proteins. The above findings indicate that when infected with CLas, lemon exhibits stronger antioxidative activity and higher expression of disease-resistant genes, contributing to its enhanced tolerance to HLB. In contrast, Shatangju shows lower antioxidative activity, reduced expression of disease-resistant genes, significant ion leakage, and extensive callose deposition, possibly related to damage to plant cell structure and blockage of phloem sieve tubes, thereby promoting the development of HLB symptoms.
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Affiliation(s)
- Muhammad Saqib Bilal
- Key Laboratory of Plant Immunity, College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China; (M.S.B.); (G.P.); (Z.Y.); (L.X.); (T.C.)
| | - Gomes Paul
- Key Laboratory of Plant Immunity, College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China; (M.S.B.); (G.P.); (Z.Y.); (L.X.); (T.C.)
| | - Ze Yu
- Key Laboratory of Plant Immunity, College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China; (M.S.B.); (G.P.); (Z.Y.); (L.X.); (T.C.)
| | - Le Xu
- Key Laboratory of Plant Immunity, College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China; (M.S.B.); (G.P.); (Z.Y.); (L.X.); (T.C.)
| | - Tang Cheng
- Key Laboratory of Plant Immunity, College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China; (M.S.B.); (G.P.); (Z.Y.); (L.X.); (T.C.)
| | - Baoping Cheng
- Institute of Plant Protection, Guangdong Academy of Agricultural Sciences/Key Laboratory of Green Prevention and Control on Fruits and Vegetables in South China, Ministry of Agriculture and Rural Affairs/Guangdong Provincial Key Laboratory of High Technology for Plant Protection, Guangzhou 510642, China
| | - Muhammad Naveed Aslam
- Department of Plant Pathology, Faculty of Agriculture and Environment, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan;
| | - Ayesha Baig
- Department of Biotechnology, COMSATS University Islamabad Abbottabad Campus, Abbottabad 22010, Pakistan;
| | - Hongwei Zhao
- Key Laboratory of Plant Immunity, College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China; (M.S.B.); (G.P.); (Z.Y.); (L.X.); (T.C.)
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4
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Singh K, Huff M, Liu J, Park JW, Rickman T, Keremane M, Krueger RR, Kunta M, Roose ML, Dardick C, Staton M, Ramadugu C. Chromosome-Scale, De Novo, Phased Genome Assemblies of Three Australian Limes: Citrus australasica, C. inodora, and C. glauca. PLANTS (BASEL, SWITZERLAND) 2024; 13:1460. [PMID: 38891269 PMCID: PMC11174732 DOI: 10.3390/plants13111460] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2024] [Revised: 05/14/2024] [Accepted: 05/20/2024] [Indexed: 06/21/2024]
Abstract
Huanglongbing (HLB) is a severe citrus disease worldwide. Wild Australian limes like Citrus australasica, C. inodora, and C. glauca possess beneficial HLB resistance traits. Individual trees of the three taxa were extensively used in a breeding program for over a decade to introgress resistance traits into commercial-quality citrus germplasm. We generated high-quality, phased, de novo genome assemblies of the three Australian limes using PacBio long-read sequencing. The genome assembly sizes of the primary and alternate haplotypes were determined for C. australasica (337 Mb/335 Mb), C. inodora (304 Mb/299 Mb), and C. glauca (376 Mb/379 Mb). The nine chromosome-scale scaffolds included 86-91% of the genome sequences generated. The integrity and completeness of the assembled genomes were estimated to be at 97.2-98.8%. Gene annotation studies identified 25,461 genes in C. australasica, 27,665 in C. inodora, and 30,067 in C. glauca. Genes belonging to 118 orthogroups were specific to Australian lime genomes compared to other citrus genomes analyzed. Significantly fewer canonical resistance (R) genes were found in C. inodora and C. glauca (319 and 449, respectively) compared to C. australasica (576), C. clementina (579), and C. sinensis (651). Similar patterns were observed for other gene families associated with potential HLB resistance, including Phloem protein 2 (PP2) and Callose synthase (CalS) genes predicted in the Australian lime genomes. The genomic information on Australian limes developed in the present study will help understand the genetic basis of HLB resistance.
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Affiliation(s)
- Khushwant Singh
- Department of Botany and Plant Sciences, University of California, Riverside, CA 92521, USA; (K.S.); (M.L.R.)
| | - Matthew Huff
- Department of Entomology and Plant Pathology, University of Tennessee, Knoxville, TN 37996, USA; (M.H.); (T.R.); (M.S.)
| | - Jianyang Liu
- Innovative Fruit Production, Improvement, and Protection, Appalachian Fruit Research Station, USDA-ARS, Kearneysville, WV 25430, USA; (J.L.); (C.D.)
| | - Jong-Won Park
- Citrus Center, Texas A&M University-Kingsville, Weslaco, TX 78599, USA; (J.-W.P.); (M.K.)
| | - Tara Rickman
- Department of Entomology and Plant Pathology, University of Tennessee, Knoxville, TN 37996, USA; (M.H.); (T.R.); (M.S.)
| | - Manjunath Keremane
- National Clonal Germplasm Repository for Citrus and Dates, USDA-ARS, Riverside, CA 92507, USA; (M.K.); (R.R.K.)
| | - Robert R. Krueger
- National Clonal Germplasm Repository for Citrus and Dates, USDA-ARS, Riverside, CA 92507, USA; (M.K.); (R.R.K.)
| | - Madhurababu Kunta
- Citrus Center, Texas A&M University-Kingsville, Weslaco, TX 78599, USA; (J.-W.P.); (M.K.)
| | - Mikeal L. Roose
- Department of Botany and Plant Sciences, University of California, Riverside, CA 92521, USA; (K.S.); (M.L.R.)
| | - Chris Dardick
- Innovative Fruit Production, Improvement, and Protection, Appalachian Fruit Research Station, USDA-ARS, Kearneysville, WV 25430, USA; (J.L.); (C.D.)
| | - Margaret Staton
- Department of Entomology and Plant Pathology, University of Tennessee, Knoxville, TN 37996, USA; (M.H.); (T.R.); (M.S.)
| | - Chandrika Ramadugu
- Department of Botany and Plant Sciences, University of California, Riverside, CA 92521, USA; (K.S.); (M.L.R.)
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Robledo J, Welker S, Shtein I, Bernardini C, Vincent C, Levy A. Phloem and Xylem Responses Are Both Implicated in Huanglongbing Tolerance of Sugar Belle. PHYTOPATHOLOGY 2024; 114:441-453. [PMID: 37551959 DOI: 10.1094/phyto-05-23-0148-r] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/09/2023]
Abstract
Although huanglongbing (HLB) is a devastating citrus disease, improved tolerant cultivars, such as Sugar Belle (SB) mandarin, have been identified. To understand the responses that HLB-affected SB undergoes, we compared 14CO2 fixation, carbohydrate export, phloem callose accumulation, relative expression of plant defense activators, and anatomical changes between healthy and infected SB trees versus susceptible Pineapple (PA) sweet orange. Eight- to ten-week-old leaves of infected SB showed a 2.5-fold increase in 14CO2 fixation and a 13% decrease in 14C-carbohydrate export, whereas HLB-affected PA presented a decrease of 33 and 50%, respectively. The mean distance of a callose deposit to its closest neighbor was 36% smaller in infected SB versus healthy, whereas in HLB-affected PA, it was 33% higher. Expression of papain-like cysteine proteases (PLCPs) was upregulated in SB but downregulated in PA. Infected SB showed minor alterations in the number of xylem vessels, a 16% larger xylem vessel lumen area, and a 14% increase in the proportional area of the xylem. In contrast, PA showed a 2.4-fold increase in the xylem vessel number and a 2% increase in the proportional xylem area. Three complementary mechanisms of tolerance in SB are hypothesized: (i) increased carbohydrate availability induced by greater CO2 fixation, mild effect in carbohydrate export, and local accumulation of callose in the phloem; (ii) activation of defense response via upregulation of PLCPs, and (iii) increased investment in the xylem structure. Thus, phloem and xylem modifications seem to be involved in SB tolerance.
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Affiliation(s)
- Jacobo Robledo
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, U.S.A
- Department of Plant Pathology, University of Florida, Gainesville, FL 32611, U.S.A
| | - Stacy Welker
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, U.S.A
| | - Ilana Shtein
- Eastern Region Research and Development Center, Ariel, Israel
| | - Chiara Bernardini
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, U.S.A
| | - Christopher Vincent
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, U.S.A
- Horticultural Sciences Department, University of Florida, Gainesville, FL 32611, U.S.A
| | - Amit Levy
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, U.S.A
- Department of Plant Pathology, University of Florida, Gainesville, FL 32611, U.S.A
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Khalilzadeh M, Lin CY, Wang C, El-Mohtar CA, Levy A. Stem-pitting caused by Citrus tristeza virus is associated with increased phloem occlusion. Virology 2024; 589:109918. [PMID: 37944362 DOI: 10.1016/j.virol.2023.109918] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2023] [Revised: 10/11/2023] [Accepted: 10/20/2023] [Indexed: 11/12/2023]
Abstract
Stem-pitting (SP) disease results from disruption of normal phloem and xylem development. In citrus, a characteristic manifestation of SP caused by Citrus tristeza virus (CTV) is phloem regeneration. We hypothesized that phloem regeneration occurs due to reduced functionality of CTV infected phloem cells. To examine phloem cell occlusions in CTV-SP, we analyzed callose and phloem-protein (PP) accumulation in Citrus macrophylla trees infected with CTV mutants exhibiting different SP phenotypes from very mild (CTVΔp13) to severe (CTVΔp33), in addition to full-length CTV and healthy plants. CTV infection was accompanied by callose and PP accumulation in the phloem. With the increase in the SP symptoms from very mild to severe, there was a constant increase in the levels of callose and PP, accompanied by an increase in PHLOEM-PROTEIN 2 and a decrease in BETA-1,3-GLUCANASE gene expression levels. These results indicate that SP symptom development is associated with increased phloem occlusion.
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Affiliation(s)
- Maryam Khalilzadeh
- Department of Plant Pathology, University of Florida, Gainesville, FL, USA; Citrus Research and Education Center, University of Florida, Lake Alfred, FL, USA
| | - Chun-Yi Lin
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL, USA
| | - Chunxia Wang
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL, USA
| | - Choaa Amine El-Mohtar
- Department of Plant Pathology, University of Florida, Gainesville, FL, USA; Citrus Research and Education Center, University of Florida, Lake Alfred, FL, USA
| | - Amit Levy
- Department of Plant Pathology, University of Florida, Gainesville, FL, USA; Citrus Research and Education Center, University of Florida, Lake Alfred, FL, USA.
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Makam SN, Setamou M, Alabi OJ, Day W, Cromey D, Nwugo C. Mitigation of Huanglongbing: Implications of a Biologically Enhanced Nutritional Program on Yield, Pathogen Localization, and Host Gene Expression Profiles. PLANT DISEASE 2023; 107:3996-4009. [PMID: 37415358 DOI: 10.1094/pdis-10-22-2336-re] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/08/2023]
Abstract
Huanglongbing (HLB, citrus greening disease), the most destructive disease affecting citrus production, is primarily linked to the gram-negative, insect-vectored, phloem-inhabiting α-proteobacterium 'Candidatus Liberibacter asiaticus' (CLas). With no effective treatment available, management strategies have largely focused on the use of insecticides in addition to the destruction of infected trees, which are environmentally hazardous and cost-prohibitive for growers, respectively. A major limitation to combating HLB is the inability to isolate CLas in axenic culture, which hinders in vitro studies and creates a need for robust in situ CLas detection and visualization methods. The aim of this study was to investigate the efficacy of a nutritional program-based approach for HLB treatment, and to explore the effectiveness of an enhanced immunodetection method to detect CLas-infected tissues. To achieve this, four different biologically enhanced nutritional programs (bENPs; P1, P2, P3, and P4) were tested on CLas-infected citrus trees. Structured illumination microscopy preceded by a modified immunolabeling process and transmission electron microscopy were used to show treatment-dependent reduction of CLas cells in phloem tissues. No sieve pore plugging was seen in the leaves of P2 trees. This was accompanied by an 80% annual increase in fruit number per tree and 1,503 (611 upregulated and 892 downregulated) differentially expressed genes. These included an MLRQ subunit gene, UDP-glucose transferase, and genes associated with the alpha-amino linolenic acid metabolism pathway in P2 trees. Taken together, the results highlight a major role for bENPs as a viable, sustainable, and cost effective option for HLB management.
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Affiliation(s)
- Srinivas N Makam
- Integrated Life Science Research Center (ILSRC), Goodyear, AZ 85338
| | - Mamoudou Setamou
- Texas A&M University-Kingsville Citrus Center, Weslaco, TX 78599
| | - Olufemi J Alabi
- Plant Pathology and Microbiology, Texas A&M AgriLife Research and Extension Center, Weslaco, TX 78596
| | - William Day
- The Imaging Cores Life Sciences North, Research, Innovation and Impact Department, University of Arizona, Tucson, AZ 85719
| | - Douglas Cromey
- The Imaging Cores Life Sciences North, Research, Innovation and Impact Department, University of Arizona, Tucson, AZ 85719
| | - Chika Nwugo
- Integrated Life Science Research Center (ILSRC), Goodyear, AZ 85338
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Cheng B, Xu L, Bilal MS, Huang Q, Niu D, Ma H, Zhou S, Peng A, Wei G, Chen F, Zeng L, Lin H, Baig A, Wang X, Zou X, Zhao H. Small RNAs contribute to citrus Huanglongbing tolerance by manipulating methyl salicylate signaling and exogenous methyl salicylate primes citrus groves from emerging infection. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2023; 116:1309-1324. [PMID: 37614043 DOI: 10.1111/tpj.16426] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2021] [Revised: 07/14/2023] [Accepted: 08/01/2023] [Indexed: 08/25/2023]
Abstract
Citrus production is severely threatened by the devastating Huanglongbing (HLB) disease globally. By studying and analyzing the defensive behaviors of an HLB-tolerant citrus cultivar 'Shatangju', we discovered that citrus can sense Candidatus Liberibacter asiaticus (CLas) infection and induce immune responses against HLB, which can be further strengthened by both endogenously produced and exogenously applied methyl salicylate (MeSA). This immune circuit is turned on by an miR2977-SAMT (encoding a citrus Salicylate [SA] O-methyltransferase) cascade, by which CLas infection leads to more in planta MeSA production and aerial emission. We provided both transgenic and multi-year trail evidences that MeSA is an effective community immune signal. Ambient MeSA accumulation and foliage application can effectively induce defense gene expression and significantly boost citrus performance. We also found that miRNAs are battle fields between citrus and CLas, and about 30% of the differential gene expression upon CLas infection are regulated by miRNAs. Furthermore, CLas hijacks host key processes by manipulating key citrus miRNAs, and citrus employs miRNAs that coordinately regulate defense-related genes. Based on our results, we proposed that miRNAs and associated components are key targets for engineering or breeding resistant citrus varieties. We anticipate that MeSA-based management, either induced expression or external application, would be a promising tool for HLB control.
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Affiliation(s)
- Baoping Cheng
- Plant Protection Research Institute, Guangdong Academy of Agricultural Sciences/Guangdong Provincial Key Laboratory of High Technology for Plant Protection, Guangzhou, 510640, China
- Key Laboratory of Green Prevention and Control on Fruits and Vegetables in South China, Ministry of Agriculture and Rural Affairs, Guangzhou, Guangdong, 510642, China
| | - Le Xu
- College of Plant Protection, Nanjing Agricultural University, Nanjing, 210095, China
- The Key Laboratory of Plant Immunity, Nanjing Agricultural University, Nanjing, 210095, China
| | - Muhammad Saqib Bilal
- College of Plant Protection, Nanjing Agricultural University, Nanjing, 210095, China
- The Key Laboratory of Plant Immunity, Nanjing Agricultural University, Nanjing, 210095, China
| | - Qing Huang
- College of Plant Protection, Nanjing Agricultural University, Nanjing, 210095, China
- The Key Laboratory of Plant Immunity, Nanjing Agricultural University, Nanjing, 210095, China
| | - Dongdong Niu
- College of Plant Protection, Nanjing Agricultural University, Nanjing, 210095, China
- The Key Laboratory of Plant Immunity, Nanjing Agricultural University, Nanjing, 210095, China
| | - Hongyu Ma
- College of Plant Protection, Nanjing Agricultural University, Nanjing, 210095, China
- The Key Laboratory of Plant Immunity, Nanjing Agricultural University, Nanjing, 210095, China
| | - Shaoxia Zhou
- College of Plant Protection, Nanjing Agricultural University, Nanjing, 210095, China
- The Key Laboratory of Plant Immunity, Nanjing Agricultural University, Nanjing, 210095, China
| | - Aitian Peng
- Plant Protection Research Institute, Guangdong Academy of Agricultural Sciences/Guangdong Provincial Key Laboratory of High Technology for Plant Protection, Guangzhou, 510640, China
- Key Laboratory of Green Prevention and Control on Fruits and Vegetables in South China, Ministry of Agriculture and Rural Affairs, Guangzhou, Guangdong, 510642, China
| | - Guo Wei
- Department of Plant Sciences, University of Tennessee, Knoxville, Tennessee, 37996, USA
| | - Feng Chen
- Department of Plant Sciences, University of Tennessee, Knoxville, Tennessee, 37996, USA
| | - Liang Zeng
- Biozeron Biotech. Co., Ltd., Shanghai, 200120, China
| | - Hong Lin
- San Joaquin Valley Agricultural Sciences Center, USDA-ARS, Parlier, California, 93658, USA
| | - Ayesha Baig
- Department of Biotechnology, COMSATS University Islamabad Abbottabad Campus, Abbottabad, KPK, 22010, Pakistan
| | - Xuefeng Wang
- National Citrus Engineering Research Center, Citrus Research Institute, Southwest University, Beibei, Chongqing, 400712, China
| | - Xiuping Zou
- National Citrus Engineering Research Center, Citrus Research Institute, Southwest University, Beibei, Chongqing, 400712, China
| | - Hongwei Zhao
- College of Plant Protection, Nanjing Agricultural University, Nanjing, 210095, China
- The Key Laboratory of Plant Immunity, Nanjing Agricultural University, Nanjing, 210095, China
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Nehela Y, Killiny N. Gamma-Aminobutyric Acid Supplementation Boosts the Phytohormonal Profile in ' Candidatus Liberibacter asiaticus'-Infected Citrus. PLANTS (BASEL, SWITZERLAND) 2023; 12:3647. [PMID: 37896110 PMCID: PMC10609878 DOI: 10.3390/plants12203647] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2023] [Revised: 10/17/2023] [Accepted: 10/18/2023] [Indexed: 10/29/2023]
Abstract
The devastating citrus disease, Huanglongbing (HLB), is associated with 'Candidatus Liberibacter sp.' and transmitted by citrus psyllids. Unfortunately, HLB has no known sustainable cure yet. Herein, we proposed γ-aminobutyric acid (GABA) as a potential eco-friendly therapeutic solution to HLB. Herein, we used GC/MS-based targeted metabolomics combined with gene expression to investigate the role of GABA in citrus response against HLB and to better understand its relationship(s) with different phytohormones. GABA supplementation via root drench boosts the accumulation of endogenous GABA in the leaves of both healthy and 'Ca. L. asiaticus'-infected trees. GABA accumulation benefits the activation of a multi-layered defensive system via modulating the phytohormone levels and regulating the expression of their biosynthesis genes and some pathogenesis-related proteins (PRs) in both healthy and 'Ca. L. asiaticus'-infected plants. Moreover, our findings showed that GABA application stimulates auxin biosynthesis in 'Ca. L. asiaticus'-infected plants via the activation of the indole-3-pyruvate (I3PA) pathway, not via the tryptamine (TAM)-dependent pathway, to enhance the growth of HLB-affected trees. Likewise, GABA accumulation was associated with the upregulation of SA biosynthesis genes, particularly the PAL-dependent route, resulting in higher SA levels that activated CsPR1, CsPR2, CsPR5, and CsWRKY70, which are prominent to activation of the SA-mediated pathway. Additionally, higher GABA levels were correlated with an enhanced JA profile and linked with both CsPR3 and CsPR4, which activates the JA-mediated pathway. Collectively, our findings suggest that exogenous GABA application might be a promising alternative and eco-friendly strategy that helps citrus trees battle HLB.
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Affiliation(s)
- Yasser Nehela
- Department of Plant Pathology, Citrus Research and Education Center, University of Florida, 700 Experiment Station Rd., Lake Alfred, FL 33850, USA;
- Department of Agricultural Botany, Faculty of Agriculture, Tanta University, Tanta 31527, Egypt
| | - Nabil Killiny
- Department of Plant Pathology, Citrus Research and Education Center, University of Florida, 700 Experiment Station Rd., Lake Alfred, FL 33850, USA;
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10
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Shi H, Yang Z, Huang J, Wu H, Fu S, Li W, Zou X, Zhou C, Wang X. An effector of 'Candidatus Liberibacter asiaticus' manipulates autophagy to promote bacterial infection. JOURNAL OF EXPERIMENTAL BOTANY 2023; 74:4670-4684. [PMID: 37166404 DOI: 10.1093/jxb/erad176] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Accepted: 05/10/2023] [Indexed: 05/12/2023]
Abstract
Autophagy functions in plant host immunity responses to pathogen infection. The molecular mechanisms and functions used by the citrus Huanglongbing (HLB)-associated intracellular bacterium 'Candidatus Liberibacter asiaticus' (CLas) to manipulate autophagy are unknown. We identified a CLas effector, SDE4405 (CLIBASIA_04405), which contributes to HLB progression. 'Wanjincheng' orange (Citrus sinensis) transgenic plants expressing SDE4405 promotes CLas proliferation and symptom expression via suppressing host immunity responses. SDE4405 interacts with the ATG8-family of proteins (ATG8s), and their interactions activate autophagy in Nicotiana benthamiana. The occurrence of autophagy is also significantly enhanced in SDE4405-transgenic citrus plants. Interrupting NbATG8s-SDE4405 interaction by silencing of NbATG8c reduces Pseudomonas syringae pv. tomato strain DC3000ΔhopQ1-1 (Pst DC3000ΔhopQ1-1) proliferation in N. benthamiana, and transient overexpression of CsATG8c and SDE4405 in citrus promotes Xanthomonas citri subsp. citri (Xcc) multiplication, suggesting that SDE4405-ATG8s interaction negatively regulates plant defense. These results demonstrate the role of the CLas effector protein in manipulating autophagy, and provide new molecular insights into the interaction between CLas and citrus hosts.
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Affiliation(s)
- Hongwei Shi
- National Citrus Engineering Research Center, Citrus Research Institute, Southwest University, Chongqing 400712, China
| | - Zuhui Yang
- National Citrus Engineering Research Center, Citrus Research Institute, Southwest University, Chongqing 400712, China
| | - Jie Huang
- National Citrus Engineering Research Center, Citrus Research Institute, Southwest University, Chongqing 400712, China
| | - Haodi Wu
- National Citrus Engineering Research Center, Citrus Research Institute, Southwest University, Chongqing 400712, China
| | - Shimin Fu
- National Citrus Engineering Research Center, Citrus Research Institute, Southwest University, Chongqing 400712, China
| | - Weimin Li
- Key Laboratory for Northern Urban Agriculture of Ministry of Agriculture and Rural Affairs, Beijing University of Agriculture, Beijing 102206, China
| | - Xiuping Zou
- National Citrus Engineering Research Center, Citrus Research Institute, Southwest University, Chongqing 400712, China
| | - Changyong Zhou
- National Citrus Engineering Research Center, Citrus Research Institute, Southwest University, Chongqing 400712, China
| | - Xuefeng Wang
- National Citrus Engineering Research Center, Citrus Research Institute, Southwest University, Chongqing 400712, China
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11
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Zhang S, Wang X, He J, Zhang S, Zhao T, Fu S, Zhou C. A Sec-dependent effector, CLIBASIA_04425, contributes to virulence in ' Candidatus Liberibater asiaticus'. FRONTIERS IN PLANT SCIENCE 2023; 14:1224736. [PMID: 37554557 PMCID: PMC10405523 DOI: 10.3389/fpls.2023.1224736] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/18/2023] [Accepted: 07/05/2023] [Indexed: 08/10/2023]
Abstract
Citrus Huanglongbing (HLB) is the most destructive citrus disease worldwide, mainly caused by 'Candidatus Liberibacter asiaticus' (CLas). It encodes a large number of Sec-dependent effectors that contribute to HLB progression. In this study, an elicitor triggering ROS burst and cell death in Nicotiana benthamiana, CLIBASIA_04425 (CLas4425), was identified. Of particular interest, its cell death-inducing activity is associated with its subcellular localization and the cytoplasmic receptor Botrytis-induced kinase 1 (BIK1). Compared with CLas infected psyllids, CLas4425 showed higher expression level in planta. The transient expression of CLas4425 in N. benthamiana and its overexpression in Citrus sinensis enhanced plant susceptibility to Pseudomonas syringae pv. tomato DC3000 ΔhopQ1-1 and CLas, respectively. Furthermore, the salicylic acid (SA) level along with the expression of genes NPR1/EDS1/NDR1/PRs in SA signal transduction was repressed in CLas4425 transgenic citrus plants. Taken together, CLas4425 is a virulence factor that promotes CLas proliferation, likely by interfering with SA-mediated plant immunity. The results obtained facilitate our understanding of CLas pathogenesis.
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Affiliation(s)
- Shushe Zhang
- Citrus Research Institute, Southwest University/National Citrus Engineering Research Center, Chongqing, China
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Chinese Academy of Agriculture Sciences, Institute of Plant Protection, Beijing, China
| | - Xuefeng Wang
- Citrus Research Institute, Southwest University/National Citrus Engineering Research Center, Chongqing, China
| | - Jun He
- Citrus Research Institute, Southwest University/National Citrus Engineering Research Center, Chongqing, China
| | - Song Zhang
- Guangxi Citrus Breeding and Cultivation Engineering Technology Center Academy of Specialty Crops, Guangxi, Guilin, China
| | - Tingchang Zhao
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Chinese Academy of Agriculture Sciences, Institute of Plant Protection, Beijing, China
| | - Shimin Fu
- Citrus Research Institute, Southwest University/National Citrus Engineering Research Center, Chongqing, China
| | - Changyong Zhou
- Citrus Research Institute, Southwest University/National Citrus Engineering Research Center, Chongqing, China
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12
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Pandey SS, Xu J, Achor DS, Li J, Wang N. Microscopic and Transcriptomic Analyses of Early Events Triggered by ' Candidatus Liberibacter asiaticus' in Young Flushes of Huanglongbing-Positive Citrus Trees. PHYTOPATHOLOGY 2023; 113:985-997. [PMID: 36449527 DOI: 10.1094/phyto-10-22-0360-r] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
'Candidatus Liberibacter asiaticus' (CLas) is associated with the devastating citrus disease Huanglongbing (HLB). Young flushes are the center of the HLB pathosystem due to their roles in the psyllid life cycle and in the acquisition and transmission of CLas. However, the early events of CLas infection and how CLas modulates young flush physiology remain poorly understood. Here, transmission electron microscopy analysis showed that the mean diameter of the sieve pores decreased in young leaves of HLB-positive trees after CLas infection, consistent with CLas-triggered callose deposition. RNA-seq-based global expression analysis of young leaves of HLB-positive sweet orange with (CLas-Pos) and without (CLas-Neg) detectable CLas demonstrated a significant impact on gene expression in young leaves, including on the expression of genes involved in host immunity, stress response, and plant hormone biosynthesis and signaling. CLas-Pos and CLas-Neg expression data displayed distinct patterns. The number of upregulated genes was higher than that of the downregulated genes in CLas-Pos for plant-pathogen interactions, glutathione metabolism, peroxisome, and calcium signaling, which are commonly associated with pathogen infections, compared with the healthy control. On the contrary, the number of upregulated genes was lower than that of the downregulated genes in CLas-Neg for genes involved in plant-pathogen interactions and peroxisome biogenesis/metabolism. Additionally, a time-course quantitative reverse transcription-PCR-based expression analysis visualized the induced expression of companion cell-specific genes, phloem protein 2 genes, and sucrose transport genes in young flushes triggered by CLas. This study advances our understanding of early events during CLas infection of citrus young flushes.
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Affiliation(s)
- Sheo Shankar Pandey
- Citrus Research and Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL 33850
| | - Jin Xu
- Citrus Research and Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL 33850
| | - Diann S Achor
- Citrus Research and Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL 33850
| | - Jinyun Li
- Citrus Research and Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL 33850
| | - Nian Wang
- Citrus Research and Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL 33850
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Chen L, Liu Y, Wu F, Zhang J, Cui X, Wu S, Deng X, Xu M. Citrus tristeza virus Promotes the Acquisition and Transmission of ‘Candidatus Liberibacter Asiaticus’ by Diaphorina citri. Viruses 2023; 15:v15040918. [PMID: 37112898 PMCID: PMC10143984 DOI: 10.3390/v15040918] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2023] [Revised: 03/24/2023] [Accepted: 04/02/2023] [Indexed: 04/07/2023] Open
Abstract
Diaphorina citri Kuwayama (D. citri) is an insect vector of phloem-limited ‘Candidatus Liberibacter asiatus’ (CLas), the presumed pathogen of citrus Huanglongbing (HLB). Recently, our lab has preliminarily found it acquired and transmitted Citrus tristeza virus (CTV), which was previously suggested to be vectored by species of aphids. However, the influences of one of the pathogens on the acquisition and transmission efficiency of the other pathogen remain unknown. In this study, CLas and CTV acquisition and transmission by D. citri at different development stages under field and laboratory conditions were determined. CTV could be detected from the nymphs, adults, and honeydew of D. citri but not from the eggs and exuviates of them. CLas in plants might inhibit CTV acquisition by D. citri as lower CTV–positive rates and CTV titers were detected in D. citri collected from HLB-affected trees compared to those from CLas–free trees. D. citri were more likely to obtain CTV than CLas from host plants co-infected with the two pathogens. Intriguingly, CTV in D. citri facilitated the acquisition and transmission of CLas, but CLas carried by D. citri had no significant effect on the transmission of CTV by the same vector. Molecular detection and microscopy methods confirmed the enrichment of CTV in the midgut after a 72-h acquisition access period. Collectively, these results raise essential scientific questions for further research on the molecular mechanism of pathogen transmission by D. citri and provide new ideas for the comprehensive prevention and control of HLB and CTV.
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Affiliation(s)
- Longtong Chen
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, Citrus Huanglongbing Research Laboratory, South China Agricultural University, Guangzhou 510642, China
| | - Yangyang Liu
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, Citrus Huanglongbing Research Laboratory, South China Agricultural University, Guangzhou 510642, China
| | - Fengnian Wu
- School of Life Sciences and Food Engineering, Hanshan Normal University, Chaozhou 521041, China
| | - Jingtian Zhang
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, Citrus Huanglongbing Research Laboratory, South China Agricultural University, Guangzhou 510642, China
| | - Xiaoqing Cui
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, Citrus Huanglongbing Research Laboratory, South China Agricultural University, Guangzhou 510642, China
| | - Shitong Wu
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, Citrus Huanglongbing Research Laboratory, South China Agricultural University, Guangzhou 510642, China
| | - Xiaoling Deng
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, Citrus Huanglongbing Research Laboratory, South China Agricultural University, Guangzhou 510642, China
| | - Meirong Xu
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, Citrus Huanglongbing Research Laboratory, South China Agricultural University, Guangzhou 510642, China
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14
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Levy A, Livingston T, Wang C, Achor D, Vashisth T. Canopy Density, but Not Bacterial Titers, Predicts Fruit Yield in Huanglongbing-Affected Sweet Orange Trees. PLANTS (BASEL, SWITZERLAND) 2023; 12:290. [PMID: 36679003 PMCID: PMC9863558 DOI: 10.3390/plants12020290] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/24/2022] [Revised: 12/05/2022] [Accepted: 12/08/2022] [Indexed: 06/17/2023]
Abstract
In Florida, almost all citrus trees are affected with Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus (CLas). We characterized various parameters of HLB-affected sweet orange trees in response to yield-improving nutritional treatment, including canopy volume, canopy density and CLas Ct values, and found that the treatment improved yield and maintained canopy density for over three years, whereas untreated HLB-affected trees declined in canopy density. The nutritional treatment did not affect CLas titer or the tree canopy volume suggesting that canopy density is a better indicator of fruit yield. To further validate the importance of canopy density, we evaluated three independent orchards (different in tree age or variety) to identify the specific traits that are correlated with fruit yields. We found that canopy density and fruit detachment force (FDF), were positively correlated with fruit yields in independent trials. Canopy density accurately distinguished between mild and severe trees in three field trials. High and low producing HLB trees had the same Ct values. Ct values did not always agree with CLas number in the phloem, as visualized by transmission electron microscopy. Our work identifies canopy density as an efficient trait to predict yields of HLB-affected trees and suggests canopy health is more relevant for yields than the CLas population.
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Affiliation(s)
- Amit Levy
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, USA
- Department of Plant Pathology, University of Florida, Gainesville, FL 32611, USA
| | - Taylor Livingston
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, USA
| | - Chunxia Wang
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, USA
| | - Diann Achor
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, USA
| | - Tripti Vashisth
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, USA
- Horticultural Sciences, University of Florida, Gainesville, FL 32611, USA
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15
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Aknadibossian V, Huguet-Tapia JC, Golyaev V, Pooggin MM, Folimonova SY. Transcriptomic alterations in the sweet orange vasculature correlate with growth repression induced by a variant of citrus tristeza virus. Front Microbiol 2023; 14:1162613. [PMID: 37138615 PMCID: PMC10150063 DOI: 10.3389/fmicb.2023.1162613] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2023] [Accepted: 03/29/2023] [Indexed: 05/05/2023] Open
Abstract
Citrus tristeza virus (CTV, family Closteroviridae) is an economically important pathogen of citrus. CTV resides in the phloem of the infected plants and induces a range of disease phenotypes, including stem pitting and quick decline as well as a number of other deleterious syndromes. To uncover the biological processes underlying the poorly understood damaging symptoms of CTV, we profiled the transcriptome of sweet orange (Citrus sinensis) phloem-rich bark tissues of non-infected, mock-inoculated trees and trees singly infected with two distinct variants of CTV, T36 or T68-1. The T36 and T68-1 variants accumulated in the infected plants at similar titers. With that, young trees infected with T68-1 were markedly repressed in growth, while the growth rate of the trees infected with T36 was comparable to the mock-inoculated trees. Only a small number of differentially expressed genes (DEGs) were identified in the nearly asymptomatic T36-infected trees, whereas almost fourfold the number of DEGs were identified with the growth-restricting T68-1 infection. DEGs were validated using quantitative reverse transcription-PCR. While T36 did not induce many noteworthy changes, T68-1 altered the expression of numerous host mRNAs encoding proteins within significant biological pathways, including immunity and stress response proteins, papain-like cysteine proteases (PLCPs), cell-wall modifying enzymes, vascular development proteins and others. The transcriptomic alterations in the T68-1-infected trees, in particular, the strong and persistent increase in the expression levels of PLCPs, appear to contribute to the observed stem growth repression. On the other hand, analysis of the viral small interfering RNAs revealed that the host RNA silencing-based response to the infection by T36 and that by T68-1 was comparable, and thus, the induction of this antiviral mechanism may not contribute to the difference in the observed symptoms. The DEGs identified in this study promote our understanding of the underlying mechanisms of the yet unexplained growth repression induced by severe CTV isolates in sweet orange trees.
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Affiliation(s)
- Vicken Aknadibossian
- Department of Plant Pathology, University of Florida, Gainesville, FL, United States
| | - Jose C. Huguet-Tapia
- Department of Plant Pathology, University of Florida, Gainesville, FL, United States
| | - Victor Golyaev
- PHIM Plant Health Institute, University Montpellier, CIRAD, INRAE, IRD, Institute Agro, Montpellier, France
| | - Mikhail M. Pooggin
- PHIM Plant Health Institute, University Montpellier, CIRAD, INRAE, IRD, Institute Agro, Montpellier, France
| | - Svetlana Y. Folimonova
- Department of Plant Pathology, University of Florida, Gainesville, FL, United States
- *Correspondence: Svetlana Y. Folimonova,
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Aidoo OF, Souza PGC, da Silva RS, Júnior PAS, Picanço MC, Kyerematen R, Sétamou M, Ekesi S, Borgemeister C. Predicting the potential global distribution of an invasive alien pest Trioza erytreae (Del Guercio) (Hemiptera: Triozidae). Sci Rep 2022; 12:20312. [PMID: 36434029 PMCID: PMC9700837 DOI: 10.1038/s41598-022-23213-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2022] [Accepted: 10/26/2022] [Indexed: 11/27/2022] Open
Abstract
The impact of invasive alien pests on agriculture, food security, and biodiversity conservation has been worsened by climate change caused by the rising earth's atmospheric greenhouse gases. The African citrus triozid, Trioza erytreae (Del Guercio; Hemiptera: Triozidae), is an invasive pest of all citrus species. It vectors the phloem-limited bacterium "Candidatus Liberibacter africanus", a causal agent of citrus greening disease or African Huanglongbing (HLB). Understanding the global distribution of T. erytreae is critical for surveillance, monitoring, and eradication programs. Therefore, we combined geospatial and physiological data of T. erytreae to predict its global distribution using the CLIMEX model. The model's prediction matches T. erytreae present-day distribution and shows that parts of the Mediterranean region have moderate (0 < EI < 30) to high (EI > 30) suitability for the pest. The model predicts habitat suitability in the major citrus-producing countries, such as Mexico, Brazil, China, India, and the USA. In the Special Report on Emissions Scenarios (SRES) A1B and A2 scenarios, the model predicts a reduction in habitat suitability from the current time to 2070. The findings show that global citrus production will continue to be threatened by T. erytreae. However, our study provides relevant information for biosecurity and risk assessment.
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Affiliation(s)
- Owusu Fordjour Aidoo
- Department of Biological, Physical and Mathematical Sciences, School of Natural and Environmental Sciences, University of Environment and Sustainable Development, Somanya, Ghana
| | - Philipe Guilherme Corcino Souza
- grid.411287.90000 0004 0643 9823Department of Agronomy, Universidade Federal dos Vales do Jequitinhonha e Mucuri (UFVJM), Diamantina, MG 39100-000 Brazil
| | - Ricardo Siqueira da Silva
- grid.411287.90000 0004 0643 9823Department of Agronomy, Universidade Federal dos Vales do Jequitinhonha e Mucuri (UFVJM), Diamantina, MG 39100-000 Brazil
| | - Paulo Antonio Santana Júnior
- grid.12799.340000 0000 8338 6359Department of Entomology, Universidade Federal de Viçosa, Av. P. H. Rolfs, s/n, Viçosa, MG 36570-900 Brazil
| | - Marcelo Coutinho Picanço
- grid.12799.340000 0000 8338 6359Department of Entomology, Universidade Federal de Viçosa, Av. P. H. Rolfs, s/n, Viçosa, MG 36570-900 Brazil
| | - Rosina Kyerematen
- grid.8652.90000 0004 1937 1485Department of Animal Biology and Conservation Sciences (DABCS), University of Ghana, P.O. Box LG 67, Legon-Accra, Ghana
| | - Mamoudou Sétamou
- grid.264760.10000 0004 0387 0036Citrus Center, Texas A&M University-Kingsville, 312 N. International Blvd., Weslaco, TX 78599 USA
| | - Sunday Ekesi
- grid.419326.b0000 0004 1794 5158Plant Health Theme, International Centre of Insect Physiology and Ecology (Icipe), P.O. Box 30772-00100, Nairobi, Kenya
| | - Christian Borgemeister
- grid.10388.320000 0001 2240 3300Centre for Development Research (ZEF), University of Bonn, Genscherallee 3, 53113 Bonn, Germany
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17
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Garcia L, Molina MC, Padgett-Pagliai KA, Torres PS, Bruna RE, García Véscovi E, González CF, Gadea J, Marano MR. A serralysin-like protein of Candidatus Liberibacter asiaticus modulates components of the bacterial extracellular matrix. Front Microbiol 2022; 13:1006962. [DOI: 10.3389/fmicb.2022.1006962] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Accepted: 09/26/2022] [Indexed: 11/13/2022] Open
Abstract
Huanglongbing (HLB), the current major threat for Citrus species, is caused by intracellular alphaproteobacteria of the genus Candidatus Liberibacter (CaL), with CaL asiaticus (CLas) being the most prevalent species. This bacterium inhabits phloem cells and is transmitted by the psyllid Diaphorina citri. A gene encoding a putative serralysin-like metalloprotease (CLIBASIA_01345) was identified in the CLas genome. The expression levels of this gene were found to be higher in citrus leaves than in psyllids, suggesting a function for this protease in adaptation to the plant environment. Here, we study the putative role of CLas-serralysin (Las1345) as virulence factor. We first assayed whether Las1345 could be secreted by two different surrogate bacteria, Rhizobium leguminosarum bv. viciae A34 (A34) and Serratia marcescens. The protein was detected only in the cellular fraction of A34 and S. marcescens expressing Las1345, and increased protease activity of those bacteria by 2.55 and 4.25-fold, respectively. In contrast, Las1345 expressed in Nicotiana benthamiana leaves did not show protease activity nor alterations in the cell membrane, suggesting that Las1345 do not function as a protease in the plant cell. Las1345 expression negatively regulated cell motility, exopolysaccharide production, and biofilm formation in Xanthomonas campestris pv. campestris (Xcc). This bacterial phenotype was correlated with reduced growth and survival on leaf surfaces as well as reduced disease symptoms in N. benthamiana and Arabidopsis. These results support a model where Las1345 could modify extracellular components to adapt bacterial shape and appendages to the phloem environment, thus contributing to virulence.
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18
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Huang Y, Zhu F, Koh J, Stanton D, Chen S, Wang N. Proteomic and bioinformatic analyses of proteins in the outer membrane and extracellular compartments and outer membrane vesicles of Candidatus Liberibacter species. Front Microbiol 2022; 13:977710. [PMID: 36225379 PMCID: PMC9548881 DOI: 10.3389/fmicb.2022.977710] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Accepted: 09/02/2022] [Indexed: 11/23/2022] Open
Abstract
Citrus Huanglongbing (HLB) is the most devastating citrus disease in the world. Candidatus Liberibacter asiaticus (Las) is the prevalent HLB pathogen, which is yet to be cultivated. A recent study demonstrates that Las does not contain pathogenicity factors that are directly responsible for HLB symptoms. Instead, Las triggers systemic and chronic immune responses, representing a pathogen-triggered immune disease. Importantly, overproduction of reactive oxygen species (ROS) causes systemic cell death of phloem tissues, thus causing HLB symptoms. Because Las resides in the phloem tissues, it is expected that phloem cell might recognize outer membrane proteins, outer membrane vesicle (OMV) proteins and extracellular proteins of Las to contribute to the immune responses. Because Las has not been cultivated, we used Liberibacter crescens (Lcr) as a surrogate to identify proteins in the OM fraction, OMV proteins and extracellular proteins by liquid chromatography with tandem mass spectrometry (LC–MS/MS). We observed OMVs of Lcr under scanning electron microscope, representing the first experimental evidence that Liberibacter can deliver proteins to the extracellular compartment. In addition, we also further analyzed LC–MS/MS data using bioinformatic tools. Our study provides valuable information regarding the biology of Ca. Liberibacter species and identifies many putative proteins that may interact with host proteins in the phloem tissues.
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Affiliation(s)
- Yixiao Huang
- Department of Plant Pathology, Citrus Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL, United States
| | - Fanchao Zhu
- Proteomics and Mass Spectrometry, Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, FL, United States
| | - Jin Koh
- Proteomics and Mass Spectrometry, Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, FL, United States
| | - Daniel Stanton
- Department of Plant Pathology, Citrus Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL, United States
| | - Sixue Chen
- Proteomics and Mass Spectrometry, Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, FL, United States
| | - Nian Wang
- Citrus Research and Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL, United States
- *Correspondence: Nian Wang,
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19
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Pulici JDVS, Murata MM, Johnson EG. Early Physiological Plant Response and Systemic Effects of Huanglongbing Infection in Split-Root Plants. PHYTOPATHOLOGY 2022; 112:1833-1843. [PMID: 35345903 DOI: 10.1094/phyto-07-21-0293-fi] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Huanglongbing (HLB), caused by 'Candidatus Liberibacter asiaticus' (CLas), is a devastating disease of citrus. After initial infection, CLas quickly colonizes the root system before canopy symptoms develop. There is limited understanding of CLas movement from roots to canopy and local and systemic effects on root dynamics. Using split-root rhizoboxes and late summer below-the-split bud inoculation, effects of local infection on systemic disease development were studied. Upward bacterial movement from roots is linked to seasonal flushes and CLas population in roots. CLas stayed isolated to one side of the roots for at least 8 months, until the spring flush. HLB caused differential root responses depending on tree age at infection. Systemic effects, independent of CLas movement, occur very early after infection. Stimulation of root growth occurred on noninfected roots prior to CLas detection in 1.5-year-old trees but decreased in 2.5-year-old trees. Independent of tree age, root growth was stimulated during spring root flushes after CLas population stabilized. Root dieback began simultaneously with detection of CLas in roots (6 weeks postinoculation). Infection and tree age altered root lifespan. In total, 1.5-year-old CLas-infected roots from summer and fall flushes had 3 and 6 weeks reduced lifespan. In contrast, 2.5-year-old CLas-infected plants lifespan was unaffected. Season affected root lifespan with late summer root flush lifespan was three times shorter than fall or spring root flushes. Split-root inoculation allowed study of local and systemic effects of CLas infection in roots, information crucial to prolonging the productivity of HLB-affected trees.
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Affiliation(s)
| | - Mayara M Murata
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850
| | - Evan G Johnson
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850
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20
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Abstract
Although the phloem is a highly specialized tissue, certain pathogens, including phytoplasmas, spiroplasmas, and viruses, have evolved to access and live in this sequestered and protected environment, causing substantial economic harm. In particular, Candidatus Liberibacter spp. are devastating citrus in many parts of the world. Given that most phloem pathogens are vectored, they are not exposed to applied chemicals and are therefore difficult to control. Furthermore, pathogens use the phloem network to escape mounted defenses. Our review summarizes the current knowledge of phloem anatomy, physiology, and biochemistry relevant to phloem/pathogen interactions. We focus on aspects of anatomy specific to pathogen movement, including sieve plate structure and phloem-specific proteins. Phloem sampling techniques are discussed. Finally, pathogens that cause particular harm to the phloem of crop species are considered in detail.
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Affiliation(s)
- Jennifer D Lewis
- Plant Gene Expression Center, USDA-ARS, Albany, California, USA
- Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, California, USA
| | - Michael Knoblauch
- School of Biological Sciences, Washington State University, Pullman, Washington, USA
| | - Robert Turgeon
- Plant Biology Section, School of Integrative Plant Science, Cornell University, Ithaca, New York, USA;
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21
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Yang B, Li X, Wu L, Chen Y, Zhong F, Liu Y, Zhao F, Ye D, Weng H. Citrus Huanglongbing detection and semi-quantification of the carbohydrate concentration based on micro-FTIR spectroscopy. Anal Bioanal Chem 2022; 414:6881-6897. [PMID: 35947156 DOI: 10.1007/s00216-022-04254-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Revised: 07/08/2022] [Accepted: 07/25/2022] [Indexed: 12/01/2022]
Abstract
Citrus Huanglongbing (HLB) is nowadays one of the most fatal citrus diseases worldwide. Once the citrus tree is infected by the HLB disease, the biochemistry of the phloem region in midribs would change. In order to investigate the carbohydrate changes in phloem region of citrus midrib, the semi-quantification models were established to predict the carbohydrate concentration in it based on Fourier transform infrared microscopy (micro-FTIR) spectroscopy coupled with chemometrics. Healthy, asymptomatic-HLB, symptomatic-HLB, and nutrient-deficient citrus midribs were collected in this study. The results showed that the intensity of the characteristic peak varied with the carbohydrate (starch and soluble sugar) concentration in citrus midrib, especially at the fingerprint regions of 1175-900 cm-1, 1500-1175 cm-1, and 1800-1500 cm-1. Furthermore, semi-quantitative prediction models of starch and soluble sugar were established using the full micro-FTIR spectra and selected characteristic wavebands. The least squares support vector machine regression (LS-SVR) model combined with the random frog (RF) algorithm achieved the best prediction result with the determination coefficient of prediction ([Formula: see text]) of 0.85, the root mean square error of prediction (RMSEP) of 0.36%, residual predictive deviation (RPD) of 2.54, and [Formula: see text] of 0.87, RMSEP of 0.37%, RPD of 2.76, for starch and soluble sugar concentration prediction, respectively. In addition, multi-layer perceptron (MLP) classification models were established to identify HLB disease, achieving the overall classification accuracy of 94% and 87%, based on the full-range spectra and the optimal wavenumbers selected by the random frog (RF) algorithm, respectively. The results demonstrated that micro-FTIR spectroscopy can be a valuable tool for the prediction of carbohydrate concentration in citrus midribs and the detection of HLB disease, which would provide useful guidelines to detect citrus HLB disease.
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Affiliation(s)
- Biyun Yang
- College of Mechanical and Electrical Engineering, Fujian Agriculture and Forestry University, Fuzhou, 350002, China.,Fujian Key Laboratory of Agricultural Information Sensing Technology, Fuzhou, 350002, China
| | - Xiaobin Li
- College of Mechanical and Electrical Engineering, Fujian Agriculture and Forestry University, Fuzhou, 350002, China.,Fujian Key Laboratory of Agricultural Information Sensing Technology, Fuzhou, 350002, China
| | - Lianwei Wu
- Fujian Institute of Testing Technology, Fuzhou, 350003, China
| | - Yayong Chen
- College of Mechanical and Electrical Engineering, Fujian Agriculture and Forestry University, Fuzhou, 350002, China.,Fujian Key Laboratory of Agricultural Information Sensing Technology, Fuzhou, 350002, China
| | - Fenglin Zhong
- College of Horticulture, Fujian Agriculture and Forestry University, Fuzhou, 350002, China
| | - Yunshi Liu
- College of Agriculture, Fujian Agriculture and Forestry University, Fuzhou, 350002, China
| | - Fei Zhao
- Fujian Institute of Testing Technology, Fuzhou, 350003, China
| | - Dapeng Ye
- College of Mechanical and Electrical Engineering, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. .,Fujian Key Laboratory of Agricultural Information Sensing Technology, Fuzhou, 350002, China.
| | - Haiyong Weng
- College of Mechanical and Electrical Engineering, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. .,Fujian Key Laboratory of Agricultural Information Sensing Technology, Fuzhou, 350002, China.
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22
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Du J, Wang Q, Zeng C, Zhou C, Wang X. A prophage-encoded nonclassical secretory protein of "Candidatus Liberibacter asiaticus" induces a strong immune response in Nicotiana benthamiana and citrus. MOLECULAR PLANT PATHOLOGY 2022; 23:1022-1034. [PMID: 35279937 PMCID: PMC9190977 DOI: 10.1111/mpp.13206] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2021] [Revised: 02/14/2022] [Accepted: 02/23/2022] [Indexed: 05/04/2023]
Abstract
Huanglongbing (HLB), associated with "Candidatus Liberibacter asiaticus" (CLas), is a globally devastating plant disease. The highly reduced genome of CLas encodes a number of secretory proteins. The conserved prophage-encoded protein AGH17470 is herein identified as a nonclassical secretory protein. We confirmed that the N-terminal and C-terminal sequences jointly determine the secretion of AGH17470. The transient expression of AGH17470 protein in Nicotiana benthamiana caused hypersensitive response (HR) cell death in infiltrated leaves and systemically infected leaves as well as the dwarfing of the entire plant, suggesting that AGH17470 is involved in the plant immune response, growth, and development. Overexpression of AGH17470 in N. benthamiana and citrus plants up-regulated the transcription of pathogenesis-related and salicylic acid (SA)-signalling pathway genes and promoted SA accumulation. Furthermore, transient expression of AGH17470 enhanced the resistance of sweet orange to Xanthomonas citri subsp. citri. To our knowledge, AGH17470 is the first prophage-encoded secretory protein demonstrated to elicit an HR and induce a strong plant immune response. The findings have increased our understanding of prophage-encoded secretory protein genes, and the results provide clues as to the plant defence response against CLas.
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Affiliation(s)
- Jiao Du
- National Citrus Engineering Research CenterCitrus Research InstituteSouthwest UniversityChongqingChina
| | - Qiying Wang
- National Citrus Engineering Research CenterCitrus Research InstituteSouthwest UniversityChongqingChina
| | - Chunhua Zeng
- National Citrus Engineering Research CenterCitrus Research InstituteSouthwest UniversityChongqingChina
| | - Changyong Zhou
- National Citrus Engineering Research CenterCitrus Research InstituteSouthwest UniversityChongqingChina
| | - Xuefeng Wang
- National Citrus Engineering Research CenterCitrus Research InstituteSouthwest UniversityChongqingChina
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23
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Srivastava AK, Das AK, Jagannadham PTK, Bora P, Ansari FA, Bhate R. Bioprospecting Microbiome for Soil and Plant Health Management Amidst Huanglongbing Threat in Citrus: A Review. FRONTIERS IN PLANT SCIENCE 2022; 13:858842. [PMID: 35557712 PMCID: PMC9088001 DOI: 10.3389/fpls.2022.858842] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Accepted: 03/21/2022] [Indexed: 06/15/2023]
Abstract
Microorganisms have dynamic and complex interactions with their hosts. Diverse microbial communities residing near, on, and within the plants, called phytobiome, are an essential part of plant health and productivity. Exploiting citrus-associated microbiomes represents a scientific approach toward sustained and environment-friendly module of citrus production, though periodically exposed to several threats, with Huanglongbing (HLB) predominantly being most influential. Exploring the composition and function of the citrus microbiome, and possible microbial redesigning under HLB disease pressure has sparked renewed interest in recent times. A concise account of various achievements in understanding the citrus-associated microbiome, in various niche environments viz., rhizosphere, phyllosphere, endosphere, and core microbiota alongside their functional attributes has been thoroughly reviewed and presented. Efforts were also made to analyze the actual role of the citrus microbiome in soil fertility and resilience, interaction with and suppression of invading pathogens along with native microbial communities and their consequences thereupon. Despite the desired potential of the citrus microbiota to counter different pathogenic diseases, utilizing the citrus microbiome for beneficial applications at the field level is yet to be translated as a commercial product. We anticipate that advancement in multiomics technologies, high-throughput sequencing and culturing, genome editing tools, artificial intelligence, and microbial consortia will provide some exciting avenues for citrus microbiome research and microbial manipulation to improve the health and productivity of citrus plants.
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Affiliation(s)
- Anoop Kumar Srivastava
- Indian Council of Agricultural Research (ICAR)-Central Citrus Research Institute, Nagpur, India
| | - Ashis Kumar Das
- Indian Council of Agricultural Research (ICAR)-Central Citrus Research Institute, Nagpur, India
| | | | - Popy Bora
- Department of Plant Pathology, Assam Agricultural University, Jorhat, India
| | - Firoz Ahmad Ansari
- Indian Council of Agricultural Research (ICAR)-Central Citrus Research Institute, Nagpur, India
| | - Ruchi Bhate
- Indian Council of Agricultural Research (ICAR)-Central Citrus Research Institute, Nagpur, India
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24
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Jain M, Cai L, Black I, Azadi P, Carlson RW, Jones KM, Gabriel DW. ' Candidatus Liberibacter asiaticus'-Encoded BCP Peroxiredoxin Suppresses Lipopolysaccharide-Mediated Defense Signaling and Nitrosative Stress In Planta. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2022; 35:257-273. [PMID: 34931906 DOI: 10.1094/mpmi-09-21-0230-r] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The lipopolysaccharides (LPS) of gram-negative bacteria trigger a nitrosative and oxidative burst in both animals and plants during pathogen invasion. Liberibacter crescens strain BT-1 is a surrogate for functional genomic studies of the uncultured pathogenic 'Candidatus Liberibacter' spp. that are associated with severe diseases such as citrus greening and potato zebra chip. Structural determination of L. crescens LPS revealed the presence of a very long chain fatty acid modification. L. crescens LPS pretreatment suppressed growth of Xanthomonas perforans on nonhost tobacco (Nicotiana benthamiana) and X. citri subsp. citri on host orange (Citrus sinensis), confirming bioactivity of L. crescens LPS in activation of systemic acquired resistance (SAR). L. crescens LPS elicited a rapid burst of nitric oxide (NO) in suspension cultured tobacco cells. Pharmacological inhibitor assays confirmed that arginine-utilizing NO synthase (NOS) activity was the primary source of NO generation elicited by L. crescens LPS. LPS treatment also resulted in biological markers of NO-mediated SAR activation, including an increase in the glutathione pool, callose deposition, and activation of the salicylic acid and azelaic acid (AzA) signaling networks. Transient expression of 'Ca. L. asiaticus' bacterioferritin comigratory protein (BCP) peroxiredoxin in tobacco compromised AzA signaling, a prerequisite for LPS-triggered SAR. Western blot analyses revealed that 'Ca. L. asiaticus' BCP peroxiredoxin prevented peroxynitrite-mediated tyrosine nitration in tobacco. 'Ca. L. asiaticus' BCP peroxiredoxin (i) attenuates NO-mediated SAR signaling and (ii) scavenges peroxynitrite radicals, which would facilitate repetitive cycles of 'Ca. L. asiaticus' acquisition and transmission by fecund psyllids throughout the limited flush period in citrus.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.
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Affiliation(s)
- Mukesh Jain
- Plant Pathology Department, University of Florida, Gainesville, FL 32611, U.S.A
| | - Lulu Cai
- Plant Pathology Department, University of Florida, Gainesville, FL 32611, U.S.A
| | - Ian Black
- Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602, U.S.A
| | - Parastoo Azadi
- Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602, U.S.A
| | - Russell W Carlson
- Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602, U.S.A
| | - Kathryn M Jones
- Department of Biological Science, Florida State University, Tallahassee, FL 32306, U.S.A
| | - Dean W Gabriel
- Plant Pathology Department, University of Florida, Gainesville, FL 32611, U.S.A
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25
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Welker S, Pierre M, Santiago JP, Dutt M, Vincent C, Levy A. Phloem transport limitation in Huanglongbing-affected sweet orange is dependent on phloem-limited bacteria and callose. TREE PHYSIOLOGY 2022; 42:379-390. [PMID: 34617106 DOI: 10.1093/treephys/tpab134] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Accepted: 10/01/2021] [Indexed: 05/11/2023]
Abstract
Huanglongbing (HLB), caused by Candidatus `Liberibacter asiaticus' (CLas), is a phloem-limited disease that disrupts citrus production in affected areas. In HLB-affected plants, phloem sieve plate pores accumulate callose, and leaf carbohydrate export is reduced. However, whether HLB causes a reduction in carbohydrate phloem translocation speed and the quantitative relationships among callose, CLas population and phloem translocation are still unknown. In this work, a procedure was developed to concurrently measure sugar transport, callose deposition and relative pathogen population at different locations throughout the stem. Increasing quantities of CLas genetic material were positively correlated with quantity and density of callose deposits and negatively correlated with phloem translocation speed. Callose deposit quantity was position and rootstock dependent and was negatively correlated with phloem translocation speed, suggesting a localized relationship. Remarkably, callose accumulation and phloem translocation disruption in the scion were dependent on rootstock genotype. Regression results suggested that the interaction of Ct values and number of phloem callose depositions, but not their size or density, explained the effects on translocation speed. Sucrose, starch and sink 14C label allocation data support the interpretation of a transport pathway limitation by CLas infection. This work shows that the interaction of local accumulation of callose and CLas affects phloem transport. Furthermore, the extent of this accumulation is attenuated by the rootstock and provides important information about the disease mechanism of phloem-inhabiting bacteria. Together, these results constitute the first example of a demonstrated transport limitation of phloem function by a microbial infection.
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Affiliation(s)
- Stacy Welker
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, USA
- Department of Plant Pathology, University of Florida, Gainesville, FL 32611, USA
| | - Myrtho Pierre
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, USA
| | - James P Santiago
- Plant Resilience Institute and MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA
| | - Manjul Dutt
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, USA
- Department of Horticulture, University of Florida, Gainesville, FL 32611, USA
| | - Christopher Vincent
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, USA
- Department of Horticulture, University of Florida, Gainesville, FL 32611, USA
| | - Amit Levy
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850, USA
- Department of Plant Pathology, University of Florida, Gainesville, FL 32611, USA
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26
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Cai Q, Liu C, Yuan M, Pan L, Yang Q, Zhou L. HLB induce changes in the tree physiology of citron ( Citrus medica L. var. sarcodactylis Swingle). PHYSIOLOGY AND MOLECULAR BIOLOGY OF PLANTS : AN INTERNATIONAL JOURNAL OF FUNCTIONAL PLANT BIOLOGY 2022; 28:517-531. [PMID: 35400879 PMCID: PMC8943090 DOI: 10.1007/s12298-022-01129-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Revised: 10/22/2021] [Accepted: 01/07/2022] [Indexed: 06/14/2023]
Abstract
UNLABELLED Huanglongbing (HLB) is a highly destructive disease that decreases the yield and quality of Citrus medica L. var. sarcodactylis Swingle (C. medica var. sarcodactylis) and poses a great threat to the development of the global citrus industry. To explore the influence of HLB infection on C. medica var. sarcodactylis, levels of photosynthetic pigments, malondialdehyde (MDA), and carbohydrates, as well as antioxidant enzyme activities, were measured. The results show that HLB infection decreased photosynthetic pigment content, increased MDA content and antioxidant enzyme activities, and caused various changes in carbohydrate levels in stem, fruit, and leaf tissues. Transcriptomic analysis of C. medica var. sarcodactylis was also used to identify key genes related to the carbohydrate metabolic synthesis pathway in C. medica var. sarcodactylis. The C. medica var. sarcodactylis ADP-glucose pyrophosphorylase1 (CmAGP1), CmAGP2, C. medica var. sarcodactylis Granule-bound starch synthase (CmGBSS), C. medica var. sarcodactylis Sucrose synthases1 (CmSUS1), CmSUS2, C. medica var. sarcodactylis Sucrose phosphate synthase (CmSPS), C. medica var. sarcodactylis alkaline/neutral invertase1 (CmNi1), CmNi2, CmNi3 and CmNi4 were successfully cloned and identified, and differential expression analysis showed that HLB infection significantly upregulated these genes in stems and leaves. In conclusion, HLB infection causes cellular damage, a reduction in photosynthetic capacity, decreased pathogen resistance, and severe disorders in carbohydrate metabolism in C. medica var. sarcodactylis. SUPPLEMENTARY INFORMATION The online version contains supplementary material available at 10.1007/s12298-022-01129-z.
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Affiliation(s)
- Qizhong Cai
- School of Traditional Chinese Medicine, Guangdong Pharmaceutical University, Guangdong Provincial Research Center On Good Agricultural Practice and Comprehensive Agricultural Development Engineering Technology of Cantonese Medicinal Materials, Comprehensive Experimental Station of Guangzhou, Chinese Material Medica, China Agriculture Research System (CARS-21-16), Key Laboratory of State Administration of Traditional Chinese Medicine for Production & Development of Cantonese Medicinal Materials, Guangzhou, 510006 China
| | - Changzheng Liu
- State Key Laboratory Breeding Base of Dao-Di Herbs, National Resource Center for Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing, 100700 China
| | - Meng Yuan
- Shanting District Healthealth Bureau, Zaozhuang, 277299 China
| | - Liming Pan
- School of Traditional Chinese Medicine, Guangdong Pharmaceutical University, Guangdong Provincial Research Center On Good Agricultural Practice and Comprehensive Agricultural Development Engineering Technology of Cantonese Medicinal Materials, Comprehensive Experimental Station of Guangzhou, Chinese Material Medica, China Agriculture Research System (CARS-21-16), Key Laboratory of State Administration of Traditional Chinese Medicine for Production & Development of Cantonese Medicinal Materials, Guangzhou, 510006 China
| | - Quan Yang
- School of Traditional Chinese Medicine, Guangdong Pharmaceutical University, Guangdong Provincial Research Center On Good Agricultural Practice and Comprehensive Agricultural Development Engineering Technology of Cantonese Medicinal Materials, Comprehensive Experimental Station of Guangzhou, Chinese Material Medica, China Agriculture Research System (CARS-21-16), Key Laboratory of State Administration of Traditional Chinese Medicine for Production & Development of Cantonese Medicinal Materials, Guangzhou, 510006 China
| | - Liangyun Zhou
- School of Traditional Chinese Medicine, Guangdong Pharmaceutical University, Guangdong Provincial Research Center On Good Agricultural Practice and Comprehensive Agricultural Development Engineering Technology of Cantonese Medicinal Materials, Comprehensive Experimental Station of Guangzhou, Chinese Material Medica, China Agriculture Research System (CARS-21-16), Key Laboratory of State Administration of Traditional Chinese Medicine for Production & Development of Cantonese Medicinal Materials, Guangzhou, 510006 China
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27
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Ma W, Pang Z, Huang X, Xu J, Pandey SS, Li J, Achor DS, Vasconcelos FNC, Hendrich C, Huang Y, Wang W, Lee D, Stanton D, Wang N. Citrus Huanglongbing is a pathogen-triggered immune disease that can be mitigated with antioxidants and gibberellin. Nat Commun 2022; 13:529. [PMID: 35082290 PMCID: PMC8791970 DOI: 10.1038/s41467-022-28189-9] [Citation(s) in RCA: 57] [Impact Index Per Article: 28.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Accepted: 01/04/2022] [Indexed: 12/17/2022] Open
Abstract
Huanglongbing (HLB) is a devastating disease of citrus, caused by the phloem-colonizing bacterium Candidatus Liberibacter asiaticus (CLas). Here, we present evidence that HLB is an immune-mediated disease. We show that CLas infection of Citrus sinensis stimulates systemic and chronic immune responses in phloem tissue, including callose deposition, production of reactive oxygen species (ROS) such as H2O2, and induction of immunity-related genes. The infection also upregulates genes encoding ROS-producing NADPH oxidases, and downregulates antioxidant enzyme genes, supporting that CLas causes oxidative stress. CLas-triggered ROS production localizes in phloem-enriched bark tissue and is followed by systemic cell death of companion and sieve element cells. Inhibition of ROS levels in CLas-positive stems by NADPH oxidase inhibitor diphenyleneiodonium (DPI) indicates that NADPH oxidases contribute to CLas-triggered ROS production. To investigate potential treatments, we show that addition of the growth hormone gibberellin (known to have immunoregulatory activities) upregulates genes encoding H2O2-scavenging enzymes and downregulates NADPH oxidases. Furthermore, foliar spray of HLB-affected citrus with gibberellin or antioxidants (uric acid, rutin) reduces H2O2 concentrations and cell death in phloem tissues and reduces HLB symptoms. Thus, our results indicate that HLB is an immune-mediated disease that can be mitigated with antioxidants and gibberellin.
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Affiliation(s)
- Wenxiu Ma
- Citrus Research and Education Center, Department of Microbiology and Cell Science, IFAS, University of Florida, Lake Alfred, FL, USA
| | - Zhiqian Pang
- Citrus Research and Education Center, Department of Microbiology and Cell Science, IFAS, University of Florida, Lake Alfred, FL, USA
| | - Xiaoen Huang
- Citrus Research and Education Center, Department of Microbiology and Cell Science, IFAS, University of Florida, Lake Alfred, FL, USA
| | - Jin Xu
- Citrus Research and Education Center, Department of Microbiology and Cell Science, IFAS, University of Florida, Lake Alfred, FL, USA
| | - Sheo Shankar Pandey
- Citrus Research and Education Center, Department of Microbiology and Cell Science, IFAS, University of Florida, Lake Alfred, FL, USA
| | - Jinyun Li
- Citrus Research and Education Center, Department of Microbiology and Cell Science, IFAS, University of Florida, Lake Alfred, FL, USA
| | - Diann S Achor
- Citrus Research and Education Center, Department of Microbiology and Cell Science, IFAS, University of Florida, Lake Alfred, FL, USA
| | - Fernanda N C Vasconcelos
- Citrus Research and Education Center, Department of Microbiology and Cell Science, IFAS, University of Florida, Lake Alfred, FL, USA
| | - Connor Hendrich
- Citrus Research and Education Center, Department of Microbiology and Cell Science, IFAS, University of Florida, Lake Alfred, FL, USA
| | - Yixiao Huang
- Citrus Research and Education Center, Department of Microbiology and Cell Science, IFAS, University of Florida, Lake Alfred, FL, USA
| | - Wenting Wang
- Citrus Research and Education Center, Department of Microbiology and Cell Science, IFAS, University of Florida, Lake Alfred, FL, USA
| | - Donghwan Lee
- Citrus Research and Education Center, Department of Microbiology and Cell Science, IFAS, University of Florida, Lake Alfred, FL, USA
| | - Daniel Stanton
- Citrus Research and Education Center, Department of Microbiology and Cell Science, IFAS, University of Florida, Lake Alfred, FL, USA
| | - Nian Wang
- Citrus Research and Education Center, Department of Microbiology and Cell Science, IFAS, University of Florida, Lake Alfred, FL, USA.
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28
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Killiny N. Generous Hosts: ' Candidatus Liberibacter asiaticus' Growth in Madagascar Periwinkle ( Catharanthus roseus) Highlights Its Nutritional Needs. PHYTOPATHOLOGY 2022; 112:89-100. [PMID: 34598662 DOI: 10.1094/phyto-05-21-0200-fi] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
'Candidatus Liberibacter asiaticus', the putative causal agent of citrus greening, is not available in pure culture yet. In addition to trees of citrus and citrus relatives, 'Ca. L. asiaticus' can grow in Madagascar periwinkle (Catharanthus roseus). Using gas chromatography-mass spectrometry, we compared the phloem sap composition in sweet orange 'Valencia' (Citrus sinensis) and periwinkle plants after the infection with 'Ca. L. asiaticus'. Interestingly, in contrast to our previous studies of total leaf metabolites, we found that, compared with uninfected phloem sap, the organic acids implicated in the tricarboxylic acid cycle (TCA) cycle including citrate, isocitrate, succinate, fumarate, and malate were reduced significantly in the infected phloem saps of both species. As a result of the reduction of organic acids content, the pH of infected phloem saps was increased. We hypothesize that the bacterial growth induces the mitochondrial TCA cycle in parenchyma cells to produce more of these compounds to be used as a bacterial carbon source. Once these compounds reach a low level in the phloem sap, the bacterium may send a signal, yet to be identified, to initiate a feedback loop to further induce the TCA cycle. Phloem blockage might be another reason behind the reduced translocation of TCA cycle intermediates within the phloem. The net result, localized availability of organic acids, likely benefits bacterial growth and may explain the unequal distribution of 'Ca. L. asiaticus' within infected trees. These findings may help in designing media for the pure culturing of 'Ca. L. asiaticus'.
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Affiliation(s)
- Nabil Killiny
- Department of Plant Pathology, Citrus Research and Education Center, IFAS, University of Florida, Lake Alfred, FL 33850
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29
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Pandey SS, Hendrich C, Andrade MO, Wang N. Candidatus Liberibacter: From Movement, Host Responses, to Symptom Development of Citrus Huanglongbing. PHYTOPATHOLOGY 2022; 112:55-68. [PMID: 34609203 DOI: 10.1094/phyto-08-21-0354-fi] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Candidatus Liberibacter spp. are fastidious α-proteobacteria that cause multiple diseases on plant hosts of economic importance, including the most devastating citrus disease: Huanglongbing (HLB). HLB was reported in Asia a century ago but has since spread worldwide. Understanding the pathogenesis of Candidatus Liberibacter spp. remains challenging as they are yet to be cultured in artificial media and infect the phloem, a sophisticated environment that is difficult to manipulate. Despite those challenges, tremendous progress has been made on Ca. Liberibacter pathosystems. Here, we first reviewed recent studies on genetic information of flagellar and type IV pili biosynthesis, their expression profiles, and movement of Ca. Liberibacter spp. inside the plant and insect hosts. Next, we reviewed the transcriptomic, proteomic, and metabolomic studies of susceptible and tolerant plant genotypes to Ca. Liberibacter spp. infection and how Ca. Liberibacter spp. adapt in plants. Analyses of the interactions between plants and Ca. Liberibacter spp. imply the involvement of immune response in the Ca. Liberibacter pathosystems. Lastly, we reviewed how Ca. Liberibacter spp. movement inside and interactions with plants lead to symptom development.
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Affiliation(s)
- Sheo Shankar Pandey
- Citrus Research and Education Center, Department of Microbiology and Cell Sciences, University of Florida, Lake Alfred, FL 33850, U.S.A
| | - Connor Hendrich
- Citrus Research and Education Center, Department of Microbiology and Cell Sciences, University of Florida, Lake Alfred, FL 33850, U.S.A
| | - Maxuel O Andrade
- Brazilian Biorenewables National Laboratory (LNBR), Brazilian Centre for Research in Energy and Materials (CNPEM), Campinas, SP, Brazil
| | - Nian Wang
- Citrus Research and Education Center, Department of Microbiology and Cell Sciences, University of Florida, Lake Alfred, FL 33850, U.S.A
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Weber KC, Mahmoud LM, Stanton D, Welker S, Qiu W, Grosser JW, Levy A, Dutt M. Insights into the mechanism of Huanglongbing tolerance in the Australian finger lime ( Citrus australasica). FRONTIERS IN PLANT SCIENCE 2022; 13:1019295. [PMID: 36340410 PMCID: PMC9634478 DOI: 10.3389/fpls.2022.1019295] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2022] [Accepted: 09/22/2022] [Indexed: 05/13/2023]
Abstract
The Australian finger lime (Citrus australasica) is tolerant to Huanglongbing (HLB; Citrus greening). This species can be utilized to develop HLB tolerant citrus cultivars through conventional breeding and biotechnological approaches. In this report, we conducted a comprehensive analysis of transcriptomic data following a non-choice infection assay to understand the CaLas tolerance mechanisms in the finger lime. After filtering 3,768 differentially expressed genes (DEGs), 2,396 were downregulated and 1,372 were upregulated in CaLas-infected finger lime compared to CaLas-infected HLB-susceptible 'Valencia' sweet orange. Comparative analyses revealed several DEGs belonging to cell wall, β-glucanase, proteolysis, R genes, signaling, redox state, peroxidases, glutathione-S-transferase, secondary metabolites, and pathogenesis-related (PR) proteins categories. Our results indicate that the finger lime has evolved specific redox control systems to mitigate the reactive oxygen species and modulate the plant defense response. We also identified candidate genes responsible for the production of Cys-rich secretory proteins and Pathogenesis-related 1 (PR1-like) proteins that are highly upregulated in infected finger lime relative to noninfected and infected 'Valencia' sweet orange. Additionally, the anatomical analysis of phloem and stem tissues in finger lime and 'Valencia' suggested better regeneration of phloem tissues in finger lime in response to HLB infection. Analysis of callose formation following infection revealed a significant difference in the production of callose plugs between the stem phloem of CaLas+ 'Valencia' sweet orange and finger lime. Understanding the mechanism of resistance will help the scientific community design strategies to protect trees from CaLas infection and assist citrus breeders in developing durable HLB tolerant citrus varieties.
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Affiliation(s)
- Kyle C. Weber
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL, United States
| | - Lamiaa M. Mahmoud
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL, United States
- Pomology Department, Faculty of Agriculture, Mansoura University, Mansoura, Egypt
| | - Daniel Stanton
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL, United States
| | - Stacy Welker
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL, United States
| | - Wenming Qiu
- Institute of Fruit and Tea, Hubei Academy of Agricultural Sciences, Wuhan, China
| | - Jude W. Grosser
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL, United States
| | - Amit Levy
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL, United States
| | - Manjul Dutt
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL, United States
- *Correspondence: Manjul Dutt,
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Hu B, Rao MJ, Deng X, Pandey SS, Hendrich C, Ding F, Wang N, Xu Q. Molecular signatures between citrus and Candidatus Liberibacter asiaticus. PLoS Pathog 2021; 17:e1010071. [PMID: 34882744 PMCID: PMC8659345 DOI: 10.1371/journal.ppat.1010071] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Citrus Huanglongbing (HLB), also known as citrus greening, is one of the most devastating citrus diseases worldwide. Candidatus Liberibacter asiaticus (CLas) is the most prevalent strain associated with HLB, which is yet to be cultured in vitro. None of the commercial citrus cultivars are resistant to HLB. The pathosystem of Ca. Liberibacter is complex and remains a mystery. In this review, we focus on the recent progress in genomic research on the pathogen, the interaction of host and CLas, and the influence of CLas infection on the transcripts, proteins, and metabolism of the host. We have also focused on the identification of candidate genes for CLas pathogenicity or the improvements of HLB tolerance in citrus. In the end, we propose potentially promising areas for mechanistic studies of CLas pathogenicity, defense regulators, and genetic improvement for HLB tolerance/resistance in the future.
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Affiliation(s)
- Bin Hu
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (Ministry of Agriculture), Huazhong Agricultural University, Wuhan, Hubei, China
| | - Muhammad Junaid Rao
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (Ministry of Agriculture), Huazhong Agricultural University, Wuhan, Hubei, China
| | - Xiuxin Deng
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (Ministry of Agriculture), Huazhong Agricultural University, Wuhan, Hubei, China
| | - Sheo Shankar Pandey
- Citrus Research and Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, Florida, United States of America
| | - Connor Hendrich
- Citrus Research and Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, Florida, United States of America
| | - Fang Ding
- Hubei Key Laboratory of Plant Pathology, Huazhong Agricultural University, Wuhan, Hubei, China
| | - Nian Wang
- Citrus Research and Education Center, Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, Florida, United States of America
| | - Qiang Xu
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (Ministry of Agriculture), Huazhong Agricultural University, Wuhan, Hubei, China
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Lally RD, Donaleshen K, Chirwa U, Eastridge K, Saintilnord W, Dickinson E, Murphy R, Borst S, Horgan K, Dawson K. Transcriptomic Response of Huanglongbing-Infected Citrus sinensis Following Field Application of a Microbial Fermentation Product. FRONTIERS IN PLANT SCIENCE 2021; 12:754391. [PMID: 34917102 PMCID: PMC8669595 DOI: 10.3389/fpls.2021.754391] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Accepted: 11/05/2021] [Indexed: 06/14/2023]
Abstract
Huanglongbing (HLB) is considered the most destructive disease in Citrus production and threatens the future of the industry. Microbial-derived defense elicitors have gained recognition for their role in plant defense priming. This work assessed a 5% (V/V) microbial fermentation application (MFA) and its role in the elicitation of defense responses in HLB-infected Citrus sinensis trees following a foliar application with a pump sprayer. Using a PCR detection method, HLB infection levels were monitored in healthy and infected trees for 20months. Nutrient analysis assessed N, P, K, Ca, Mg, Mn, Zn, Fe, B, and Cu concentrations in the trees. MFA significantly increased Cu concentrations in treated trees and resulted in the stabilization of disease index (DI) in infected trees. Initial real-time qPCR analysis of defense-associated genes showed a significant increase in pathogenesis-related protein 2 (PR2) and phenylalanine ammonia lyase (PAL) gene expression in healthy and HLB-infected trees in response to MFA. Gene expression of PR2 and PAL peaked 6h post-microbial fermentation application during an 8-h sampling period. A transcriptomic assessment using GeneChip microarray of the hour 6 samples revealed differential expression of 565 genes when MFA was applied to healthy trees and 909 genes when applied infected citrus trees when compared to their respective controls. There were 403 uniquely differentially expressed genes in response to MFA following an intersectional analysis of both healthy and infected citrus trees. The transcriptomic analysis revealed that several genes associated with plant development, growth, and defense were upregulated in response to MFA, including multiple PR genes, lignin formation genes, ROS-related genes, hormone synthases, and hormone regulators. This study provides further evidence that MFA may play an important role as a plant elicitor in an integrated pest management strategy in citrus and other agronomically important crops.
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Affiliation(s)
| | | | | | | | - Wesley Saintilnord
- Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, KY, United States
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Raiol-Junior LL, Cifuentes-Arenas JC, Cunniffe NJ, Turgeon R, Lopes SA. Modeling ' Candidatus Liberibacter asiaticus' Movement Within Citrus Plants. PHYTOPATHOLOGY 2021; 111:1711-1719. [PMID: 33724870 DOI: 10.1094/phyto-12-20-0559-r] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The phloem-limited 'Candidatus Liberibacter asiaticus' (Las) causes huanglongbing, a destructive citrus disease. Graft-inoculated potted plants were used to assess Las speed of movement in phloem in the greenhouse, and the impacts of temperature on plant colonization in growth-chamber experiments. For assessment of Las speed, plants were inoculated at the main stem and assessed over time by quantitative PCR (qPCR) or symptoms at various distances from the inoculum. For colonization, the plants were inoculated in one of two opposite top branches, maintained at from 8 to 20°C, from 18 to 30°C, or from 24 to 38°C daily range, and assessed by qPCR of samples taken from noninoculated shoots. For all experiments, frequencies of Las-positive sites were submitted to analysis of variance and binomial generalized linear model and logistic regression analyses. Probabilities of detecting Las in greenhouse plants were functions of time and distance from the inoculation site, which resulted in 2.9 and 3.8 cm day-1 average speed of movement. In growth chambers, the temperature impacted plant colonization by Las, new shoot emission, and symptom expression. After a 7-month exposure time, Las was absent in all new shoots in the cooler environment (average three per plant), and present in 70% at the milder environment (six shoots, severe symptoms) and 25% in the warmer environment (eight shoots, no visible symptoms). Temperature of 25.7°C was the optimum condition for plant colonization. This explains the higher impact and incidence of huanglongbing disease during the winter months or regions of milder climates in Brazil.
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Affiliation(s)
- Laudecir L Raiol-Junior
- Unversidade Estadual Paulista "Júlio de Mesquita Filho," 14884-900 Jaboticabal, São Paulo, Brazil
| | - Juan C Cifuentes-Arenas
- Unversidade Estadual Paulista "Júlio de Mesquita Filho," 14884-900 Jaboticabal, São Paulo, Brazil
- Fundo de Defesa da Citricultura, 14807-040 Araraquara, São Paulo, Brazil
| | - Nik J Cunniffe
- Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, U.K
| | - Robert Turgeon
- Department of Plant Biology, Cornell University, Ithaca, NY 14853, U.S.A
| | - Silvio A Lopes
- Fundo de Defesa da Citricultura, 14807-040 Araraquara, São Paulo, Brazil
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Merli ML, Padgett-Pagliai KA, Cuaycal AE, Garcia L, Marano MR, Lorca GL, Gonzalez CF. ' Candidatus Liberibacter asiaticus' Multimeric LotP Mediates Citrus sinensis Defense Response Activation. Front Microbiol 2021; 12:661547. [PMID: 34421834 PMCID: PMC8371691 DOI: 10.3389/fmicb.2021.661547] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2021] [Accepted: 07/06/2021] [Indexed: 11/13/2022] Open
Abstract
‘Candidatus Liberibacter asiaticus’ is known as the most pathogenic organism associated with citrus greening disease. Since its publicized emergence in Florida in 2005, ‘Ca. L. asiaticus’ remains unculturable. Currently, a limited number of potential disease effectors have been identified through in silico analysis. Therefore, these potential effectors remain poorly characterized and do not fully explain the complexity of symptoms observed in citrus trees infected with ‘Ca. L. asiaticus.’ LotP has been identified as a potential effector and have been partially characterized. This protein retains structural homology to the substrate binding domain of the Lon protease. LotP interacts with chaperones like GroEL, Hsp40, DnaJ, and ClpX and may exercise its biological role through interactions with different proteins involved in proteostasis networks. Here, we evaluate the interactome of LotP—revealing a new protein–protein interaction target (Lon-serine protease) and its effect on citrus plant tissue integrity. We found that via protein–protein interactions, LotP can enhance Lon protease activity, increasing the degradation rate of its specific targets. Infiltration of purified LotP strained citrus plant tissue causing photoinhibition and chlorosis after several days. Proteomics analysis of LotP tissues recovering after the infiltration revealed a large abundance of plant proteins associated with the stabilization and processing of mRNA transcripts, a subset of important transcription factors; and pathways associated with innate plant defense were highly expressed. Furthermore, interactions and substrate binding module of LotP suggest potential interactions with plant proteins, most likely proteases.
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Affiliation(s)
- Marcelo L Merli
- Department of Microbiology and Cell Science, Genetics Institute, Institute of Food and Agricultural Science, University of Florida, Gainesville, FL, United States
| | - Kaylie A Padgett-Pagliai
- Department of Microbiology and Cell Science, Genetics Institute, Institute of Food and Agricultural Science, University of Florida, Gainesville, FL, United States
| | - Alexandra E Cuaycal
- Department of Microbiology and Cell Science, Genetics Institute, Institute of Food and Agricultural Science, University of Florida, Gainesville, FL, United States
| | - Lucila Garcia
- Instituto de Biología Molecular y Celular de Rosario (IBR), Consejo Nacional de Investigaciones Científicas y Tecnológicas, Rosario, Argentina
| | - Maria Rosa Marano
- Instituto de Biología Molecular y Celular de Rosario (IBR), Consejo Nacional de Investigaciones Científicas y Tecnológicas, Rosario, Argentina
| | - Graciela L Lorca
- Department of Microbiology and Cell Science, Genetics Institute, Institute of Food and Agricultural Science, University of Florida, Gainesville, FL, United States
| | - Claudio F Gonzalez
- Department of Microbiology and Cell Science, Genetics Institute, Institute of Food and Agricultural Science, University of Florida, Gainesville, FL, United States
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35
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Munir S, Ahmed A, Li Y, He P, Singh BK, He P, Li X, Asad S, Wu Y, He Y. The hidden treasures of citrus: finding Huanglongbing cure where it was lost. Crit Rev Biotechnol 2021; 42:634-649. [PMID: 34325576 DOI: 10.1080/07388551.2021.1942780] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Huanglongbing (HLB), a deadly citrus disease which has significantly downsized the entire industry worldwide. The intractable and incurable disease has brought the citriculture an enormous loss of productivity. With no resistant varieties available, failure of chemical treatments despite repeated applications, and hazardous consequences to environmental health, have led to large-scale research to find a sustainable cure. Inside plants, the key determinants of health and safety, live the endophytic microbes. Endophytes possess unrivaled plant benefiting properties. The progression of HLB is known to cause disturbance in endophytic bacterial communities. Given the importance of the plant endophytic microbiome in disease progression, the notion of engineering microbiomes through indigenous endophytes is attracting scientific attention which is considered revolutionary as it precludes the incompatibility concerns associated with the use of alien (microbes from other plant species) endophytes. In this review, we briefly discuss the transformation of the plant-pathogen-environment to the plant-pathogen-microbial system in a disease triangle. We also argue the employment of indigenous endophytes isolated from a healthy state to engineer the diseased citrus endophytic microbiomes that can provide sustainable solution for vascular pathogens. We evaluated the plethora of microbiomes responses to the re-introduction of endophytes which leads to disease resistance in the citrus host. The idea is not merely confined to citrus-HLB, but it is globally applicable for tailoring a customized cure for general plant-pathogen systems particularly for the diseases caused by the vascular system-restricted pathogens.
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Affiliation(s)
- Shahzad Munir
- State Key Laboratory for Conservation and Utilization of Bio-resources in Yunnan, Yunnan Agricultural University, Kunming, P. R. China
| | - Ayesha Ahmed
- State Key Laboratory for Conservation and Utilization of Bio-resources in Yunnan, Yunnan Agricultural University, Kunming, P. R. China
| | - Yongmei Li
- State Key Laboratory for Conservation and Utilization of Bio-resources in Yunnan, Yunnan Agricultural University, Kunming, P. R. China
| | - Pengbo He
- State Key Laboratory for Conservation and Utilization of Bio-resources in Yunnan, Yunnan Agricultural University, Kunming, P. R. China
| | - Brajesh K Singh
- Hawkesbury Institute for the Environment, Western Sydney University, Penrith South, Australia.,Global Centre for Land Based Innovation, Western Sydney University, Penrith South, Australia
| | - Pengfei He
- State Key Laboratory for Conservation and Utilization of Bio-resources in Yunnan, Yunnan Agricultural University, Kunming, P. R. China
| | - Xingyu Li
- State Key Laboratory for Conservation and Utilization of Bio-resources in Yunnan, Yunnan Agricultural University, Kunming, P. R. China
| | - Suhail Asad
- State Key Laboratory for Conservation and Utilization of Bio-resources in Yunnan, Yunnan Agricultural University, Kunming, P. R. China
| | - Yixin Wu
- State Key Laboratory for Conservation and Utilization of Bio-resources in Yunnan, Yunnan Agricultural University, Kunming, P. R. China.,College of Agronomy and Biotechnology, Yunnan Agricultural University, Kunming, P. R. China
| | - Yueqiu He
- State Key Laboratory for Conservation and Utilization of Bio-resources in Yunnan, Yunnan Agricultural University, Kunming, P. R. China
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Vasconcelos FNC, Li J, Pang Z, Vincent C, Wang N. The Total Population Size of ' Candidatus Liberibacter asiaticus' Inside the Phloem of Citrus Trees and the Corresponding Metabolic Burden Related to Huanglongbing Disease Development. PHYTOPATHOLOGY 2021; 111:1122-1128. [PMID: 33090080 DOI: 10.1094/phyto-09-20-0388-r] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
'Candidatus Liberibacter asiaticus' (CLas) is the predominant causal agent of citrus huanglongbing, the most devastating citrus disease worldwide. CLas colonizes phloem tissue and causes phloem dysfunction. The pathogen population size in local tissues and in the whole plant is critical for the development of disease symptoms by determining the load of pathogenicity factors and metabolic burden to the host. However, the total population size of CLas in a whole plant and the ratio of CLas to citrus cells in local tissues have not been addressed previously. The total CLas population size for 2.5-year-old 'Valencia' sweet orange on 'Kuharske' citrange rootstock trees was quantified using quantitative PCR to be approximately 1.74 × 109 cells/tree, whereas 7- and 20-year-old sweet orange trees were estimated to be 4.3 × 1010 cells/tree, and 6.0 × 1010 cells/tree, respectively. The majority of CLas cells were distributed in leaf tissues (55.58%), followed by those in branch (36.78%), feeder root (4.75%), trunk (2.39%), and structural root (0.51%) tissues. The ratios of citrus cells to CLas cells for branch, leaf, trunk, feeder root, and structural root samples were within approximately 39 to 79, 44 to 124, 153 to 1,355, 191 to 1,054, and 561 to 3,760, respectively, representing the metabolic burden of CLas in different organs. It was estimated that the ratios of phloem cells to CLas cells for branch, leaf, trunk, feeder root, and structural root samples are approximately 0.39 to 0.79, 0.44 to 1.24, 1.53 to 13.55, 1.91 to 10.54, and 5.61 to 37.60, respectively. Approximately 0.01% of the total citrus phloem volume was estimated to be occupied by CLas, explaining the difficulty to observe CLas in most tissues under transmission electron microscopy. The CLas titer inside the leaf was estimated to be approximately 1.64 × 106 cells/leaf or 9.2 × 104 cells cm-2 in leaves, approximately 104 times less than that of typical apoplastic bacterial pathogens. This study provides quantitative estimates of phloem colonization by bacterial pathogens and furthers the understanding of the biology and virulence mechanisms of CLas.
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Affiliation(s)
- Fernanda N C Vasconcelos
- Citrus Research and Education Center (CREC), Department of Microbiology and Cell Science, University of Florida, Lake Alfred, FL 33850
| | - Jinuyn Li
- Citrus Research and Education Center (CREC), Department of Microbiology and Cell Science, University of Florida, Lake Alfred, FL 33850
| | - Zhiqian Pang
- Citrus Research and Education Center (CREC), Department of Microbiology and Cell Science, University of Florida, Lake Alfred, FL 33850
| | - Christopher Vincent
- Citrus Research and Education Center (CREC), Department of Horticultural Sciences, University of Florida, Lake Alfred, FL 33850
| | - Nian Wang
- Citrus Research and Education Center (CREC), Department of Microbiology and Cell Science, University of Florida, Lake Alfred, FL 33850
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37
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Fang F, Guo H, Zhao A, Li T, Liao H, Deng X, Xu M, Zheng Z. A Significantly High Abundance of " Candidatus Liberibacter asiaticus" in Citrus Fruit Pith: in planta Transcriptome and Anatomical Analyses. Front Microbiol 2021; 12:681251. [PMID: 34177866 PMCID: PMC8225937 DOI: 10.3389/fmicb.2021.681251] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Accepted: 05/10/2021] [Indexed: 11/20/2022] Open
Abstract
Huanglongbing, a highly destructive disease of citrus, is associated with the non-culturable phloem-limited α-proteobacterium "Candidatus Liberibacter asiaticus" (CLas). The distribution patterns of CLas in infected plant are variable and not consistent, which make the CLas detection and characterization more challenging. Here, we performed a systemic analysis of CLas distribution in citrus branches and fruits of 14 cultivars. A significantly high concentration of CLas was detected in fruit pith (dorsal vascular bundle) of 14 citrus cultivars collected at fruit maturity season. A 2-year monitoring assay of CLas population in citrus branches of "Shatangju" mandarin (Citrus reticulata Blanco "Shatangju") revealed that CLas population already exhibited a high level even before the appearance of visual symptoms in the fruit rind. Quantitative analyses of CLas in serial 1.5-cm segments of fruit piths showed the CLas was unevenly distributed within fruit pith and tended to colonize in the middle or distal (stylar end) regions of pith. The use of CLas-abundant fruit pith for dual RNA-seq generated higher-resolution CLas transcriptome data compared with the leaf samples. CLas genes involved in transport system, flagellar assembly, lipopolysaccharide biosynthesis, virulence, stress response, and cell surface structure, as well as host genes involved in biosynthesis of antimicrobial-associated secondary metabolites, was up-regulated in leaf midribs compared with fruit pith. In addition, CLas infection caused the severe collapse in phloem and callose deposition in the plasmodesmata of fruit pith. The ability of fruit pith to support multiplication of CLas to high levels makes it an ideal host tissue for morphological studies and in planta transcriptome analyses of CLas-host interactions.
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Affiliation(s)
- Fang Fang
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, South China Agricultural University, Guangzhou, China
| | - Hengyu Guo
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, South China Agricultural University, Guangzhou, China
| | - Anmin Zhao
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, South China Agricultural University, Guangzhou, China
| | - Tao Li
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, South China Agricultural University, Guangzhou, China
| | - Huihong Liao
- Horticulture Research Institute, Guangxi Academy of Agricultural Sciences, Nanning, China
| | - Xiaoling Deng
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, South China Agricultural University, Guangzhou, China
| | - Meirong Xu
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, South China Agricultural University, Guangzhou, China
| | - Zheng Zheng
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, South China Agricultural University, Guangzhou, China
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38
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Alves MN, Cifuentes-Arenas JC, Raiol-Junior LL, Ferro JA, Peña L. Early Population Dynamics of " Candidatus Liberibacter asiaticus" in Susceptible and Resistant Genotypes After Inoculation With Infected Diaphorina citri Feeding on Young Shoots. Front Microbiol 2021; 12:683923. [PMID: 34177870 PMCID: PMC8219961 DOI: 10.3389/fmicb.2021.683923] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Accepted: 04/29/2021] [Indexed: 11/14/2022] Open
Abstract
Huanglongbing is a highly destructive citrus disease associated with “Candidatus Liberibacter asiaticus” (Las), a phloem−limited and non-culturable bacterium, naturally transmitted by the psyllid Diaphorina citri. Although diverse approaches have been used to understand the molecular mechanisms involved in the pathogen–host interaction, such approaches have focused on already infected and/or symptomatic plants, missing early events in the initial days post-inoculation. This study aimed to identify the time course of Las multiplication and whole-plant colonization immediately following inoculation by infected psyllids feeding for 2 days. Thus, the experimental approach was to track Las titers after psyllid inoculation in new shoots (NS) of Citrus × sinensis (susceptible), Murraya paniculata (partially resistant), and Bergera koenigii (fully resistant). Soon after psyllid removal, Las titers dropped until the 10–12th days in all three species. Following this, Las titers increased exponentially only in C. × sinensis and M. paniculata, indicating active bacterial multiplication. In C. × sinensis, Las reached a stationary phase at ∼5 log Las cells/g of tissue from the 40th day onward, while in M. paniculata, Las increased at a lower rate of up to ∼3 log Las cells/g of tissue between the 40th and 60th days, decreasing gradually thereafter and becoming undetectable from the 160th day onward. In B. koenigii, Las titers decreased from the start and remained undetectable. In C. × sinensis, an average of 2.6 log of Las cells/g of tissue was necessary for Las to move out of 50% of the NS in 23.6 days and to colonize the rest of the plant, causing a successful infection. Conversely, the probability of Las moving out of the NS remained below 50% in M. paniculata and zero in B. koenigii. To our knowledge, this is the first study on Las dynamics and whole-plant colonization during the earliest stages of infection. Identification of critical time-points for either successful multiplication or Las resistance may help to elucidate initial events of Las–host interactions that may be missed due to longer sampling intervals and at later stages of infection.
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Affiliation(s)
- Mônica Neli Alves
- Faculdade de Ciências Agrárias e Veterinárias (FCAV), Universidade Estadual Paulista (UNESP), Jaboticabal, Brazil.,Fundo de Defesa da Citricultura (Fundecitrus), Araraquara, Brazil
| | | | | | - Jesus Aparecido Ferro
- Faculdade de Ciências Agrárias e Veterinárias (FCAV), Universidade Estadual Paulista (UNESP), Jaboticabal, Brazil
| | - Leandro Peña
- Fundo de Defesa da Citricultura (Fundecitrus), Araraquara, Brazil.,Instituto de Biología Molecular y Celular de Plantas (IBMCP), Consejo Superior de Investigaciones Científicas (CSIC), Universidad Politécnica de Valencia (UPV), Valencia, Spain
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Wei X, Mira A, Yu Q, Gmitter FG. The Mechanism of Citrus Host Defense Response Repression at Early Stages of Infection by Feeding of Diaphorina citri Transmitting Candidatus Liberibacter asiaticus. FRONTIERS IN PLANT SCIENCE 2021; 12:635153. [PMID: 34168662 PMCID: PMC8218908 DOI: 10.3389/fpls.2021.635153] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Accepted: 04/29/2021] [Indexed: 06/01/2023]
Abstract
Citrus Huanglongbing (HLB) is the most devastating disease of citrus, presumably caused by "Candidatus Liberibacter asiaticus" (CaLas). Although transcriptomic profiling of HLB-affected citrus plants has been studied extensively, the initial steps in pathogenesis have not been fully understood. In this study, RNA sequencing (RNA-seq) was used to compare very early transcriptional changes in the response of Valencia sweet orange (VAL) to CaLas after being fed by the vector, Diaphorina citri (Asian citrus psyllid, or ACP). The results suggest the existence of a delayed defense reaction against the infective vector in VAL, while the attack by the healthy vector prompted immediate and substantial transcriptomic changes that led to the rapid erection of active defenses. Moreover, in the presence of CaLas-infected psyllids, several downregulated differentially expressed genes (DEGs) were identified on the pathways, such as signaling, transcription factor, hormone, defense, and photosynthesis-related pathways at 1 day post-infestation (dpi). Surprisingly, a burst of DEGs (6,055) was detected at 5 dpi, including both upregulated and downregulated DEGs on the defense-related and secondary metabolic pathways, and severely downregulated DEGs on the photosynthesis-related pathways. Very interestingly, a significant number of those downregulated DEGs required ATP binding for the activation of phosphate as substrate; meanwhile, abundant highly upregulated DEGs were detected on the ATP biosynthetic and glycolytic pathways. These findings highlight the energy requirement of CaLas virulence processes. The emerging picture is that CaLas not only employs virulence strategies to subvert the host cell immunity, but the fast-replicating CaLas also actively rewires host cellular metabolic pathways to obtain the necessary energy and molecular building blocks to support virulence and the replication process. Taken together, the very early response of citrus to the CaLas, vectored by infective ACP, was evaluated for the first time, thus allowing the changes in gene expression relating to the primary mechanisms of susceptibility and host-pathogen interactions to be studied, and without the secondary effects caused by the development of complex whole plant symptoms.
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Affiliation(s)
- Xu Wei
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL, United States
- College of Horticulture and Landscape, Southwest University, Chongqing, China
| | - Amany Mira
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL, United States
- Department of Horticulture, Faculty of Agriculture, Tanta University, Tanta, Egypt
| | - Qibin Yu
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL, United States
| | - Fred G. Gmitter
- Citrus Research and Education Center, University of Florida, Lake Alfred, FL, United States
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40
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Pandey SS, Nogales da Costa Vasconcelos F, Wang N. Spatiotemporal Dynamics of ' Candidatus Liberibacter asiaticus' Colonization Inside Citrus Plant and Huanglongbing Disease Development. PHYTOPATHOLOGY 2021; 111:921-928. [PMID: 33174821 DOI: 10.1094/phyto-09-20-0407-r] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
'Candidatus Liberibacter asiaticus' (CLas), the causal agent of citrus huanglongbing (HLB), colonizes inside the phloem and is naturally transmitted by the Asian citrus psyllid (ACP). Here, we investigated spatiotemporal CLas colonization in different tissues after ACP transmission. Of the nine plants successfully infected via ACP transmission, CLas was detected in the roots of all trees at 75 days postremoval of ACPs (DPR) but in the mature leaf of only one tree; this finding is consistent with the model that CLas moves passively from source to sink tissues. At 75 and 365 DPR, CLas was detected in 11.1 and 43.1% of mature leaves not fed on by ACPs during transmission, respectively, unveiling active movement to the source tissue. The difference in colonization timing of sink and source tissues indicates that CLas is capable of both passive and active movement, with passive movement being dominant. At 225 DPR, leaves fed on by ACPs during the young stage showed the highest ratio of HLB symptomatic leaves and the highest CLas titer, followed by leaves that emerged after ACP removal and mature leaves not fed on by ACPs. Importantly, our data showed that ACPs were unable to transmit CLas via feeding on mature leaves. It is estimated that it takes 3 years at most for CLas to infect the whole tree. Overall, spatiotemporal detection of CLas in different tissues after ACP transmission helps visualize the infection process of CLas in planta and subsequent HLB symptom development and provides evidence showing that young leaves should be the focus of HLB management.
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Affiliation(s)
- Sheo Shankar Pandey
- Citrus Research and Education Center, Department of Microbiology and Cell Science, University of Florida, Lake Alfred, FL 33850
| | | | - Nian Wang
- Citrus Research and Education Center, Department of Microbiology and Cell Science, University of Florida, Lake Alfred, FL 33850
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41
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Differences in Leaf Morphological Parameters of Pear (Pyrus communis L.) Based on Their Susceptibility to European Pear Rust Caused by Gymnosporangium sabinae (Dicks.) Oerst. PLANTS 2021; 10:plants10051024. [PMID: 34065374 PMCID: PMC8161175 DOI: 10.3390/plants10051024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/12/2021] [Revised: 05/17/2021] [Accepted: 05/19/2021] [Indexed: 11/16/2022]
Abstract
European pear rust is an important disease; however, the relationship between its causal pathogen Gymnosporangium sabinae (Dicks.) Oerst. and host Pyrus communis L. is poorly understood. In this study, disease severity was measured, and leaf samples were collected over three years, and their leaf water content; leaf area; leaf mass per area; and epidermis, mesophyll, and vascular tissue width and stomatal density were measured and compared between susceptible and resistant genotypes for each year. Most genotypes either showed consistent disease symptoms or showed no symptoms during the study in terms of their susceptibility. A correlation between disease severity and mesophyll tissue thickness, and stomatal density and differences between several morphological parameters were found depending on the genotype’s susceptibility. The study showed that the following pear morphological traits were stable between the years: water content, leaf mass per area, spongy mesophyll thickness, phloem thickness, and stomatal density. When selecting for breeding, we found that candidates for traits that discern susceptible genotypes from resistant were mesophyll layer width, stomatal density, epidermis width, and xylem tissue width.
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Zou X, Du M, Liu Y, Wu L, Xu L, Long Q, Peng A, He Y, Andrade M, Chen S. CsLOB1 regulates susceptibility to citrus canker through promoting cell proliferation in citrus. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2021; 106:1039-1057. [PMID: 33754403 DOI: 10.1111/tpj.15217] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Revised: 02/18/2021] [Accepted: 02/23/2021] [Indexed: 05/25/2023]
Abstract
Citrus sinensis lateral organ boundary 1 (CsLOB1) was previously identified as a critical disease susceptibility gene for citrus bacterial canker, which is caused by Xanthomonas citri subsp. citri (Xcc). However, the molecular mechanisms of CsLOB1 in citrus response to Xcc are still elusive. Here, we constructed transgenic plants overexpressing and RNAi-silencing of CsLOB1 using the canker-disease susceptible 'wanjincheng' orange (C. sinensis Osbeck) as explants. CsLOB1-overexpressing plants exhibited dwarf phenotypes with smaller and thicker leaf, increased branches and adventitious buds clustered on stems. These phenotypes were followed by a process of pustule- and canker-like development that exhibited enhanced cell proliferation. Pectin depolymerization and expansin accumulation were enhanced by CsLOB1 overexpression, while cellulose and hemicellulose synthesis were increased by CsLOB1 silence. Whilst overexpression of CsLOB1 increased susceptibility, RNAi-silencing of CsLOB1 enhanced resistance to canker disease without impairing pathogen entry. Transcriptome analysis revealed that CsLOB1 positively regulated cell wall degradation and modification processes, cytokinin metabolism, and cell division. Additionally, 565 CsLOB1-targeted genes were identified in chromatin immunoprecipitation-sequencing (ChIP-seq) experiments. Motif discovery analysis revealed that the most highly overrepresented binding sites had a conserved 6-bp 'GCGGCG' consensus DNA motif. RNA-seq and ChIP-seq data suggested that CsLOB1 directly activates the expression of four genes involved in cell wall remodeling, and three genes that participate in cytokinin and brassinosteroid hormone pathways. Our findings indicate that CsLOB1 promotes cell proliferation by mechanisms depending on cell wall remodeling and phytohormone signaling, which may be critical to citrus canker development and bacterial growth in citrus.
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Affiliation(s)
- Xiuping Zou
- Citrus Research Institute, Chinese Academy of Agricultural Sciences/Southwest University, Chongqing, 400712, P. R. China
| | - Meixia Du
- Citrus Research Institute, Chinese Academy of Agricultural Sciences/Southwest University, Chongqing, 400712, P. R. China
| | - Yunuo Liu
- Citrus Research Institute, Chinese Academy of Agricultural Sciences/Southwest University, Chongqing, 400712, P. R. China
| | - Liu Wu
- Citrus Research Institute, Chinese Academy of Agricultural Sciences/Southwest University, Chongqing, 400712, P. R. China
| | - Lanzhen Xu
- Citrus Research Institute, Chinese Academy of Agricultural Sciences/Southwest University, Chongqing, 400712, P. R. China
| | - Qin Long
- Citrus Research Institute, Chinese Academy of Agricultural Sciences/Southwest University, Chongqing, 400712, P. R. China
| | - Aihong Peng
- Citrus Research Institute, Chinese Academy of Agricultural Sciences/Southwest University, Chongqing, 400712, P. R. China
| | - Yongrui He
- Citrus Research Institute, Chinese Academy of Agricultural Sciences/Southwest University, Chongqing, 400712, P. R. China
| | - Maxuel Andrade
- Brazilian Biosciences National Laboratory (LNBio), Brazilian Center for Research in Energy and Materials (CNPEM), Campinas, SP, Brazil
| | - Shanchun Chen
- Citrus Research Institute, Chinese Academy of Agricultural Sciences/Southwest University, Chongqing, 400712, P. R. China
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43
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Yao T, Zhou Y, Hu J, Xiao T, Zhou C. Genomic evolutionary relationship of SWEET genes and their responses to HLB disease and oxytetracycline treatment in Valencia sweet orange. Biologia (Bratisl) 2021. [DOI: 10.1007/s11756-021-00745-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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44
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" Candidatus Liberibacter asiaticus" Secretes Nonclassically Secreted Proteins That Suppress Host Hypersensitive Cell Death and Induce Expression of Plant Pathogenesis-Related Proteins. Appl Environ Microbiol 2021; 87:AEM.00019-21. [PMID: 33579681 PMCID: PMC8091116 DOI: 10.1128/aem.00019-21] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Although emerging evidence indicates that bacteria extracellularly export many cytoplasmic proteins referred to as non-classically secreted proteins (ncSecPs) for their own benefit, the mechanisms and functional significance of the ncSecPs in extracellular milieu remain elusive. "Candidatus Liberibacter asiaticus" (CLas) is a fastidious Gram-negative bacterium that causes Huanglongbing (HLB), the most globally devastating citrus disease. In this study, using the SecretomeP program coupled with an Escherichia coli alkaline phosphatase assay, we identified 27 ncSecPs from the CLas genome. Further, we demonstrated that 10 of these exhibited significantly higher levels of gene expression in citrus than in psyllid hosts, and particularly suppressed hypersensitive response (HR)-based cell death and H2O2 overaccumulation in Nicotiana benthamiana, indicating their opposing effects on early plant defenses. However, these proteins also dramatically enhanced the gene expression of pathogenesis-related 1 protein (PR-1), PR-2, and PR-5, essential components of plant defense mechanisms. Additional experiments disclosed that the increased expression of these PR genes, in particular PR-1 and PR-5, could negatively regulate HR-based cell death development and H2O2 accumulation. Remarkably, CLas infection clearly induced gene expression of PR-1, PR-2, and PR-5 in both HLB-tolerant and HLB-susceptible species of citrus plants. Taken together, we hypothesized that CLas has evolved an arsenal of ncSecPs that function cooperatively to overwhelm the early plant defenses by inducing host PR genes.IMPORTANCE In this study, we present a combined computational and experimental methodology that allows a rapid and efficient identification of the ncSecPs from bacteria, in particular the unculturable bacteria like CLas. Meanwhile, the study determined that a number of CLas ncSecPs suppressed HR-based cell death, and thus indicated a novel role for the bacterial ncSecPs in extracellular milieu. More importantly, these ncSecPs were found to suppress cell death presumably by utilizing host PR proteins. The data overall provide a novel clue to understand the CLas pathogenesis and also suggest a new way by which phytopathogens manipulate host cellular machinery to establish infection.
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45
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Li T, Zhang L, Deng Y, Deng X, Zheng Z. Establishment of a Cuscuta campestris-mediated enrichment system for genomic and transcriptomic analyses of 'Candidatus Liberibacter asiaticus'. Microb Biotechnol 2021; 14:737-751. [PMID: 33655703 PMCID: PMC7936317 DOI: 10.1111/1751-7915.13773] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2020] [Revised: 01/30/2021] [Accepted: 02/01/2021] [Indexed: 01/16/2023] Open
Abstract
‘Candidatus Liberibacter asiaticus’ (CLas) is a phloem‐limited non‐culturable α‐proteobacterium associated with citrus Huanglongbing, a highly destructive disease threatening global citrus industry. Research on CLas is challenging due to the current inability to culture CLas in vitro and the low CLas titre in citrus plant. Here, we develop a CLas enrichment system using the holoparasitic dodder plant (Cuscuta campestris) as an amenable host to acquire and enrich CLas from CLas‐infected citrus shoots maintained hydroponically. Forty‐eight out of fifty‐five (87%) dodder plants successfully parasitized CLas‐infected citrus shoots with detectable CLas by PCR. Among 48 dodders cultures, 30 showed two‐ to 419‐fold CLas titre increase as compared to the corresponding citrus hosts. The CLas population rapidly increased and reached the highest level in dodder tendrils at 15 days after parasitizing citrus shoot. Genome sequencing and assembly derived from CLas‐enriched dodder DNA samples generated a higher resolution than those obtained for CLas from citrus hosts. No genomic variation was detected in CLas after transmission from citrus to dodder during short‐term parasitism. Dual RNA‐Seq experiments showed similar CLas gene expression profiles in dodder and citrus samples, yet dodder samples generated a higher resolution of CLas transcriptome data. The ability of dodder to support CLas multiplication to high levels, as well as its advantage in CLas genomic and transcriptomic analyses, make it an optimal model for further studies on CLas–host interaction.
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Affiliation(s)
- Tao Li
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, South China Agricultural University, Guangzhou, Guangdong, 510642, China.,Citrus Huanglongbing Research Laboratory, South China Agricultural University, Guangzhou, Guangdong, 510642, China
| | - Ling Zhang
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, South China Agricultural University, Guangzhou, Guangdong, 510642, China.,Citrus Huanglongbing Research Laboratory, South China Agricultural University, Guangzhou, Guangdong, 510642, China
| | - Yunshuang Deng
- Citrus Huanglongbing Research Laboratory, South China Agricultural University, Guangzhou, Guangdong, 510642, China
| | - Xiaoling Deng
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, South China Agricultural University, Guangzhou, Guangdong, 510642, China.,Citrus Huanglongbing Research Laboratory, South China Agricultural University, Guangzhou, Guangdong, 510642, China
| | - Zheng Zheng
- Guangdong Province Key Laboratory of Microbial Signals and Disease Control, South China Agricultural University, Guangzhou, Guangdong, 510642, China.,Citrus Huanglongbing Research Laboratory, South China Agricultural University, Guangzhou, Guangdong, 510642, China
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46
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Nan J, Zhang S, Jiang L. Antibacterial Potential of Bacillus amyloliquefaciens GJ1 against Citrus Huanglongbing. PLANTS 2021; 10:plants10020261. [PMID: 33572917 PMCID: PMC7910844 DOI: 10.3390/plants10020261] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/26/2020] [Revised: 01/25/2021] [Accepted: 01/26/2021] [Indexed: 01/13/2023]
Abstract
Citrus huanglongbing (HLB) is a destructive disease caused by Candidatus Liberibacter species and is a serious global concern for the citrus industry. To date, there is no established strategy for control of this disease. Previously, Bacillus amyloliquefaciens GJ1 was screened as the biocontrol agent against HLB. In this study, two-year-old citrus infected by Ca. L. asiaticus were treated with B. amyloliquefaciens GJ1 solution via root irrigation. In these plants, after seven irrigation treatments, the results indicated that the photosynthetic parameters, chlorophyll content, resistance-associated enzyme content and the expression of defense-related genes were significantly higher than for the plants treated with the same volume water. The content of starch and soluble sugar were significantly lower, compared to the control treatment. The parallel reaction monitoring (PRM) results revealed that treatment with B. amyloliquefaciens GJ1 solution, the expression levels of 3 proteins with photosynthetic function were upregulated in citrus leaves. The accumulation of reactive oxygen species (ROS) in citrus leaves treated with B. amyloliquefaciens GJ1 flag22 was significantly higher than untreated plants and induced the defense-related gene expression in citrus. Finally, surfactin was identified from the fermentation broth of B. amyloliquefaciens GJ1 by high-performance liquid chromatography. These results indicate that B. amyloliquefaciens GJ1 may improve the immunity of citrus by increasing the photosynthesis and enhancing the expression of the resistance-related genes.
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Affiliation(s)
- Jing Nan
- College of Horticulture and Forestry, Ministry of Education Key Laboratory of Plant Biology, Huazhong Agricultural University, Wuhan 430070, China;
| | - Shaoran Zhang
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China;
| | - Ling Jiang
- College of Horticulture and Forestry, Ministry of Education Key Laboratory of Plant Biology, Huazhong Agricultural University, Wuhan 430070, China;
- Correspondence:
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Skipping the Insect Vector: Plant Stolon Transmission of the Phytopathogen ' Ca. Phlomobacter fragariae' from the Arsenophonus Clade of Insect Endosymbionts. INSECTS 2021; 12:insects12020093. [PMID: 33499057 PMCID: PMC7912703 DOI: 10.3390/insects12020093] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Revised: 01/14/2021] [Accepted: 01/19/2021] [Indexed: 02/06/2023]
Abstract
Simple Summary Numerous plant sap-feeding insects are vectors of plant-pathogenic bacteria that cause devastating crop diseases. Some of these bacteria had initially been insect endosymbionts that eventually evolved the capacity to survive in plants after being frequently transmitted to plants by their insect hosts during feeding. An example for this evolutionary transition is the bacterial symbiont ‘Candidatus Phlomobacter fragariae’ (hereafter Phlomobacter) of the planthopper Cixius wagneri. Upon transmission to strawberry plants by its insect vector, the bacterium accumulates in the plant phloem and causes Strawberry Marginal Chlorosis disease. Using quantitative PCR and transmission electron microscopy, we demonstrate an additional plant-to-plant transmission route: Phlomobacter can be transmitted from an infected plant to daughter plants through stolons, a specific type of stem from which daughter plants can develop. Our results show that Phlomobacter was abundant in stolons and was efficiently transmitted to daughter plants, which developed disease symptoms. Hence, Phlomobacter is not only able to survive in plants, but can even be transmitted to new plant generations, independently from its ancestral insect host. Abstract The genus Arsenophonus represents one of the most widespread clades of insect endosymbionts, including reproductive manipulators and bacteriocyte-associated primary endosymbionts. Two strains belonging to the Arsenophonus clade have been identified as insect-vectored plant pathogens of strawberry and sugar beet. The bacteria accumulate in the phloem of infected plants, ultimately causing leaf yellows and necrosis. These symbionts therefore represent excellent model systems to investigate the evolutionary transition from a purely insect-associated endosymbiont towards an insect-vectored phytopathogen. Using quantitative PCR and transmission electron microscopy, we demonstrate that ‘Candidatus Phlomobacter fragariae’, bacterial symbiont of the planthopper Cixius wagneri and the causative agent of Strawberry Marginal Chlorosis disease, can be transmitted from an infected strawberry plant to multiple daughter plants through stolons. Stolons are horizontally growing stems enabling the nutrient provisioning of daughter plants during their early growth phase. Our results show that Phlomobacter was abundant in the phloem sieve elements of stolons and was efficiently transmitted to daughter plants, which rapidly developed disease symptoms. From an evolutionary perspective, Phlomobacter is, therefore, not only able to survive within the plant after transmission by the insect vector, but can even be transmitted to new plant generations, independently from its ancestral insect host.
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Involvement of SUT1 and SUT2 Sugar Transporters in the Impairment of Sugar Transport and Changes in Phloem Exudate Contents in Phytoplasma-Infected Plants. Int J Mol Sci 2021; 22:ijms22020745. [PMID: 33451049 PMCID: PMC7828548 DOI: 10.3390/ijms22020745] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Revised: 12/30/2020] [Accepted: 01/08/2021] [Indexed: 12/18/2022] Open
Abstract
Phytoplasmas inhabit phloem sieve elements and cause abnormal growth and altered sugar partitioning. However, how they interact with phloem functions is not clearly known. The phloem responses were investigated in tomatoes infected by “Candidatus Phytoplasma solani” at the beginning of the symptomatic stage, the first symptoms appearing in the newly emerged leaf at the stem apex. Antisense lines impaired in the phloem sucrose transporters SUT1 and SUT2 were included. In symptomatic sink leaves, leaf curling was associated with higher starch accumulation and the expression of defense genes. The analysis of leaf midribs of symptomatic leaves indicated that transcript levels for genes acting in the glycolysis and peroxisome metabolism differed from these in noninfected plants. The phytoplasma also multiplied in the three lower source leaves, even if it was not associated with the symptoms. In these leaves, the rate of phloem sucrose exudation was lower for infected plants. Metabolite profiling of phloem sap-enriched exudates revealed that glycolate and aspartate levels were affected by the infection. Their levels were also affected in the noninfected SUT1- and SUT2-antisense lines. The findings suggest the role of sugar transporters in the responses to infection and describe the consequences of impaired sugar transport on the primary metabolism.
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49
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Molecular Analysis of 14-3-3 Genes in Citrus sinensis and Their Responses to Different Stresses. Int J Mol Sci 2021; 22:ijms22020568. [PMID: 33430069 PMCID: PMC7826509 DOI: 10.3390/ijms22020568] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Revised: 01/04/2021] [Accepted: 01/05/2021] [Indexed: 12/31/2022] Open
Abstract
14-3-3 proteins (14-3-3s) are among the most important phosphorylated molecules playing crucial roles in regulating plant development and defense responses to environmental constraints. No report thus far has documented the gene family of 14-3-3s in Citrus sinensis and their roles in response to stresses. In this study, nine 14-3-3 genes, designated as CitGF14s (CitGF14a through CitGF14i) were identified from the latest C. sinensis genome. Phylogenetic analysis classified them into ε-like and non-ε groups, which were supported by gene structure analysis. The nine CitGF14s were located on five chromosomes, and none had duplication. Publicly available RNA-Seq raw data and microarray databases were mined for 14-3-3 expression profiles in different organs of citrus and in response to biotic and abiotic stresses. RT-qPCR was used for further examining spatial expression patterns of CitGF14s in citrus and their temporal expressions in one-year-old C. sinensis “Xuegan” plants after being exposed to different biotic and abiotic stresses. The nine CitGF14s were expressed in eight different organs with some isoforms displayed tissue-specific expression patterns. Six of the CitGF14s positively responded to citrus canker infection (Xanthomonas axonopodis pv. citri). The CitGF14s showed expressional divergence after phytohormone application and abiotic stress treatments, suggesting that 14-3-3 proteins are ubiquitous regulators in C. sinensis. Using the yeast two-hybrid assay, CitGF14a, b, c, d, g, and h were found to interact with CitGF14i proteins to form a heterodimer, while CitGF14i interacted with itself to form a homodimer. Further analysis of CitGF14s co-expression and potential interactors established a 14-3-3s protein interaction network. The established network identified 14-3-3 genes and several candidate clients which may play an important role in developmental regulation and stress responses in this important fruit crop. This is the first study of 14-3-3s in citrus, and the established network may help further investigation of the roles of 14-3-3s in response to abiotic and biotic constraints.
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Raiol-Junior LL, Cifuentes-Arenas JC, de Carvalho EV, Girardi EA, Lopes SA. Evidence That ' Candidatus Liberibacter asiaticus' Moves Predominantly Toward New Tissue Growth in Citrus Plants. PLANT DISEASE 2021; 105:34-42. [PMID: 33201785 DOI: 10.1094/pdis-01-20-0158-re] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
'Candidatus Liberibacter asiaticus' (Las) is an unculturable, phloem-limited, insect-transmitted bacterium associated with the Asiatic form of huanglongbing (HLB), the most destructive citrus disease. In Asia and the Americas, it is transmitted by the Asian citrus psyllid (Diaphorina citri Kuwavama). Despite considerable research, little is known about the processes involved in plant infection and colonization by Las. This study was conducted to determine whether the basal portion (below girdling) of the plant is an important route for Las to move laterally from a point of inoculation on a branch to pathogen-free branches elsewhere in the canopy, and to quantify the influence of actively growing tissues on vertical upward (acropetally) or downward (basipetally) movement of Las. Nongirdled and fully or partially girdled stems of potted plants of 'Pera' sweet orange, graft-inoculated above or below girdling, were sampled in distinct regions and assessed by qPCR, 6 months postinoculation. Las invaded all regions of partially and nongirdled plants but remained restricted to the inoculated regions of fully girdled plants, evidence that in planta bacterium movement is limited to the phloem. In fully girdled plants, starch accumulated above the girdling site, probably because of changes in flow of phloem sap. To study the influence of actively growing tissues, inoculated 'Valencia' sweet orange plants were kept intact or were top- or root-pruned to force production of new tissues, and sampled at 15-day intervals. Las migrated rapidly and most predominantly toward newly developing root and leaf tissues. The rapid and predominant movement of Las to newly developed shoots and roots would explain failures of canopy heat treatments and pruning to cure HLB-affected trees, and reinforces the need to protect rapidly growing new shoots from feeding by D. citri in order to minimize transmission and spread of the pathogen by the vector within and between orchards.
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Affiliation(s)
| | | | | | - Eduardo A Girardi
- Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA), Cruz das Almas BA, Brazil
| | - Silvio A Lopes
- Fundo de Defesa da Citricultura (Fundecitrus), Araraquara SP, Brazil
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