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Dandlen SA, Da Silva JP, Miguel MG, Duarte A, Power DM, Marques NT. Quick Decline and Stem Pitting Citrus tristeza virus Isolates Induce a Distinct Metabolomic Profile and Antioxidant Enzyme Activity in the Phloem Sap of Two Citrus Species. PLANTS (BASEL, SWITZERLAND) 2023; 12:1394. [PMID: 36987082 PMCID: PMC10051153 DOI: 10.3390/plants12061394] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Revised: 03/06/2023] [Accepted: 03/14/2023] [Indexed: 06/19/2023]
Abstract
Susceptibility to the severe Citrus tristeza virus (CTV), T36, is higher for Citrus macrophylla (CM) than for C. aurantium (CA). How host-virus interactions are reflected in host physiology is largely unknown. In this study, the profile of metabolites and the antioxidant activity in the phloem sap of healthy and infected CA and CM plants were evaluated. The phloem sap of quick decline (T36) and stem pitting (T318A) infected citrus, and control plants was collected by centrifugation, and the enzymes and metabolites analyzed. The activity of the antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT), in infected plants increased significantly in CM and decreased in CA, compared to the healthy controls. Using LC-HRMS2 a metabolic profile rich in secondary metabolites was assigned to healthy CA, compared to healthy CM. CTV infection of CA caused a drastic reduction in secondary metabolites, but not in CM. In conclusion, CA and CM have a different response to severe CTV isolates and we propose that the low susceptibility of CA to T36 may be related to the interaction of the virus with the host's metabolism, which reduces significantly the synthesis of flavonoids and antioxidant enzyme activity.
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Affiliation(s)
- Susana A. Dandlen
- MED—Instituto Mediterrâneo para a Agricultura, Ambiente e Desenvolvimento, Faculdade de Ciências e Tecnologia, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
| | - José P. Da Silva
- Centre of Marine Sciences (CCMAR/CIMAR LA), Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
| | - Maria Graça Miguel
- MED—Instituto Mediterrâneo para a Agricultura, Ambiente e Desenvolvimento, Faculdade de Ciências e Tecnologia, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
| | - Amílcar Duarte
- MED—Instituto Mediterrâneo para a Agricultura, Ambiente e Desenvolvimento, Faculdade de Ciências e Tecnologia, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
| | - Deborah M. Power
- Centre of Marine Sciences (CCMAR/CIMAR LA), Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
| | - Natália Tomás Marques
- CEOT—Centro de Eletrónica, Optoeletrónica e Telecomunicações, Faculdade de Ciências e Tecnologia, Edif. 8, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
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Guarino S, Mercati F, Fatta Del Bosco S, Motisi A, Abbate L. Rootstocks with Different Tolerance Grade to Citrus Tristeza Virus Induce Dissimilar Volatile Profile in Citrus sinensis and Avoidance Response in the Vector Aphis gossypii Glover. PLANTS (BASEL, SWITZERLAND) 2022; 11:3426. [PMID: 36559538 PMCID: PMC9788239 DOI: 10.3390/plants11243426] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/16/2022] [Revised: 12/02/2022] [Accepted: 12/05/2022] [Indexed: 06/17/2023]
Abstract
The citrus tristeza virus (CTV) is an agent of devastating epidemics of the citrus plant grafted on Citrus aurantium, one of the main rootstocks still used in the Mediterranean area. Consequently, CTV-tolerant alternative citrus rootstocks are considered necessary to manage this disease and/or its vector; that in Mediterranean countries is the aphid Aphis gossypii. In this study, we analyzed the VOCs emitted from Citrus sinensis plants grafted on the CTV-susceptible C. aurantium and on the CTV-tolerant Volkamer lemon, Forner-Alcaide no. 5, and Carrizo citrange. Furthermore, the aphid preference/avoidance response toward these combinations was evaluated in a semi-field experiment. The VOC profiles recorded on the leaves of C. sinensis grafted on the four rootstocks listed above showed significant differences in the abundances and ratios of the compounds emitted. The behavioral experiments indicated that A. gossypii prefers to orient and establish on the C. sinensis plants grafted on C. aurantium rather than on that grafted on the three CTV-tolerant varieties. The possibility that this avoidance mechanism is triggered by the different profile of the VOC emitted by the different combinations and the consequent susceptibility/tolerance shown toward CTV is discussed.
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Lv C, Li F, Ai X, Bi H. H 2O 2 participates in ABA regulation of grafting-induced chilling tolerance in cucumber. PLANT CELL REPORTS 2022; 41:1115-1130. [PMID: 35260922 DOI: 10.1007/s00299-022-02841-6] [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: 11/17/2021] [Accepted: 02/01/2022] [Indexed: 05/20/2023]
Abstract
Rootstock provides more abscisic acid (ABA) content to scions to increase the chilling tolerance of seedlings. H2O2 is involved in ABA regulation of grafting-induced chilling tolerance of cucumber. Here we examined the role of ABA in the response of grafted cucumber to chilling stress. The data showed chilling induced an increase in leaf and root ABA content and there was a positive correlation between ABA content and the chilling tolerance of the varieties. The increase of ABA content and NCED mRNA abundance in the leaf of both Cs/Cs (self-root) and Cs/Cm (grafted with pumpkin as rootstock) showed a delay under aerial stress compared with those under whole plant and root-zone stress. Intriguingly, an increase in ABA in xylem was found under whole-plant and root-zone chilling stress but was not detected under aerial stress, implying the increases in ABA content in leaves were mainly from root ABA transportation. Compared to Cs/Cs, a higher ABA content and NCED mRNA abundance were observed in Cs/Cm, which showed that Cm could output more ABA than Cs. The removal of endogenous ABA decreased the difference in chilling tolerance induced by Cm, as evidenced by the observed similar oxidative stress levels and photosynthetic capacity between Cs/Cs and Cs/Cm after chilling stress. Moreover, we found that the H2O2 signal in grafted cucumber could respond to chilling stress earlier than the H2O2 signal in self-rooted cucumber. The inhibition of endogenous H2O2 decreased the chilling tolerance of grafted cucumber induced by ABA by reducing photosynthesis and the mRNA abundance of CBF1 and COR. Thus, our results indicate that H2O2, as the downstream signal, participated in the rootstock-induced chilling tolerance of grafted seedlings induced by ABA.
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Affiliation(s)
- Chunyu Lv
- State Key Laboratory of Crop Biology, Key Laboratory of Crop Biology and Genetic Improvement of Horticultural Crops in Huanghuai Region, College of Horticulture Science and Engineering, Shandong Agricultural University, Tai'an, 271018, Shandong, China
| | - Fude Li
- State Key Laboratory of Crop Biology, Key Laboratory of Crop Biology and Genetic Improvement of Horticultural Crops in Huanghuai Region, College of Horticulture Science and Engineering, Shandong Agricultural University, Tai'an, 271018, Shandong, China
| | - Xizhen Ai
- State Key Laboratory of Crop Biology, Key Laboratory of Crop Biology and Genetic Improvement of Horticultural Crops in Huanghuai Region, College of Horticulture Science and Engineering, Shandong Agricultural University, Tai'an, 271018, Shandong, China
| | - Huangai Bi
- State Key Laboratory of Crop Biology, Key Laboratory of Crop Biology and Genetic Improvement of Horticultural Crops in Huanghuai Region, College of Horticulture Science and Engineering, Shandong Agricultural University, Tai'an, 271018, Shandong, China.
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4
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Huang CY, Niu D, Kund G, Jones M, Albrecht U, Nguyen L, Bui C, Ramadugu C, Bowman KD, Trumble J, Jin H. Identification of citrus immune regulators involved in defence against Huanglongbing using a new functional screening system. PLANT BIOTECHNOLOGY JOURNAL 2021; 19:757-766. [PMID: 33108698 PMCID: PMC8051609 DOI: 10.1111/pbi.13502] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2020] [Revised: 09/27/2020] [Accepted: 10/18/2020] [Indexed: 05/24/2023]
Abstract
Huanglongbing (HLB) is the most devastating citrus disease in the world. Almost all commercial citrus varieties are susceptible to the causal bacterium, Candidatus Liberibacter asiaticus (CLas), which is transmitted by the Asian citrus psyllid (ACP). Currently, there are no effective management strategies to control HLB. HLB-tolerant traits have been reported in some citrus relatives and citrus hybrids, which offer a direct pathway for discovering natural defence regulators to combat HLB. Through comparative analysis of small RNA profiles and target gene expression between an HLB-tolerant citrus hybrid (Poncirus trifoliata × Citrus reticulata) and a susceptible citrus variety, we identified a panel of candidate defence regulators for HLB-tolerance. These regulators display similar expression patterns in another HLB-tolerant citrus relative, with a distinct genetic and geographic background, the Sydney hybrid (Microcitrus virgata). Because the functional validation of candidate regulators in tree crops is always challenging, we developed a novel rapid functional screening method, using a C. Liberibacter solanacearum (CLso)/potato psyllid/Nicotiana benthamiana interaction system to mimic the natural transmission and infection circuit of the HLB complex. When combined with efficient virus-induced gene silencing in N. benthamiana, this innovative and cost-effective screening method allows for rapid identification and functional characterization of regulators involved in plant immune responses against HLB, such as the positive regulator BRCA1-Associated Protein, and the negative regulator Vascular Associated Death Protein.
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Affiliation(s)
- Chien Yu Huang
- Department of Microbiology and Plant PathologyCenter for Plant Cell BiologyUniversity of CaliforniaRiversideCAUSA
| | - DongDong Niu
- Department of Microbiology and Plant PathologyCenter for Plant Cell BiologyUniversity of CaliforniaRiversideCAUSA
- Department of Plant ProtectionNanjing Agriculture UniversityNanjingChina
| | | | | | - Ute Albrecht
- Horticultural Sciences DepartmentSouthwest Florida Research and Education CenterUniversity of Florida/IFASImmokaleeFLUSA
| | - Lincoln Nguyen
- Department of Microbiology and Plant PathologyCenter for Plant Cell BiologyUniversity of CaliforniaRiversideCAUSA
| | - Christine Bui
- Department of Microbiology and Plant PathologyCenter for Plant Cell BiologyUniversity of CaliforniaRiversideCAUSA
| | | | - Kim D. Bowman
- US Horticultural Research LaboratoryAgricultural Research ServiceUSDAFort PierceFLUSA
| | | | - Hailing Jin
- Department of Microbiology and Plant PathologyCenter for Plant Cell BiologyUniversity of CaliforniaRiversideCAUSA
- Institute for Integrative Genome BiologyUCRCAUSA
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Huang Y, Xu Y, Jiang X, Yu H, Jia H, Tan C, Hu G, Hu Y, Rao MJ, Deng X, Xu Q. Genome of a citrus rootstock and global DNA demethylation caused by heterografting. HORTICULTURE RESEARCH 2021; 8:69. [PMID: 33790260 PMCID: PMC8012640 DOI: 10.1038/s41438-021-00505-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Revised: 12/01/2020] [Accepted: 12/29/2020] [Indexed: 05/03/2023]
Abstract
Grafting is an ancient technique used for plant propagation and improvement in horticultural crops for at least 1,500 years. Citrus plants, with a seed-to-seed cycle of 5-15 years, are among the fruit crops that were probably domesticated by grafting. Poncirus trifoliata, a widely used citrus rootstock, can promote early flowering, strengthen stress tolerance, and improve fruit quality via scion-rootstock interactions. Here, we report its genome assembly using PacBio sequencing. We obtained a final genome of 303 Mb with a contig N50 size of 1.17 Mb and annotated 25,680 protein-coding genes. DNA methylome and transcriptome analyses indicated that the strong adaptability of P. trifoliata is likely attributable to its special epigenetic modification and expression pattern of resistance-related genes. Heterografting by using sweet orange as scion and P. trifoliata as rootstock and autografting using sweet orange as both scion and rootstock were performed to investigate the genetic effects of the rootstock. Single-base methylome analysis indicated that P. trifoliata as a rootstock caused DNA demethylation and a reduction in 24-nt small RNAs (sRNAs) in scions compared to the level observed with autografting, implying the involvement of sRNA-mediated graft-transmissible epigenetic modifications in citrus grafting. Taken together, the assembled genome for the citrus rootstock and the analysis of graft-induced epigenetic modifications provide global insights into the genetic effects of rootstock-scion interactions and grafting biology.
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Affiliation(s)
- Yue Huang
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, 430070, Wuhan, China
| | - Yuantao Xu
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, 430070, Wuhan, China
| | - Xiaolin Jiang
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, 430070, Wuhan, China
| | - Huiwen Yu
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, 430070, Wuhan, China
| | - Huihui Jia
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, 430070, Wuhan, China
| | - Chunming Tan
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, 430070, Wuhan, China
| | - Gang Hu
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, 430070, Wuhan, China
| | - Yibo Hu
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, 430070, Wuhan, China
| | - Muhammad Junaid Rao
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, 430070, Wuhan, China
| | - Xiuxin Deng
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, 430070, Wuhan, China
| | - Qiang Xu
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, 430070, Wuhan, China.
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Sun YD, Folimonova SY. The p33 protein of Citrus tristeza virus affects viral pathogenicity by modulating a host immune response. THE NEW PHYTOLOGIST 2019; 221:2039-2053. [PMID: 30220089 DOI: 10.1111/nph.15482] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2018] [Accepted: 09/10/2018] [Indexed: 06/08/2023]
Abstract
Accumulation of reactive oxygen species (ROS) is a general plant basal defense strategy against viruses. In this study, we show that infection by Citrus tristeza virus (CTV) triggered ROS burst in Nicotiana benthamiana and in the natural citrus host, the extent of which was virus-dose dependent. Using Agrobacterium-mediated expression of CTV-encoded proteins in N. benthamiana, we found that p33, a unique viral protein, contributed to the induction of ROS accumulation and programmed cell death. The role of p33 in CTV pathogenicity was assessed based on gene knockout and complementation in N. benthamiana. In the citrus-CTV pathosystem, deletion of the p33 open reading frame in a CTV variant resulted in a significant decrease in ROS production, compared to that of the wild type CTV, which correlated with invasion of the mutant virus into the immature xylem tracheid cells and abnormal differentiation of the vascular system. By contrast, the wild type CTV exhibited phloem-limited distribution with a minor effect on the vasculature. We conclude that the p33 protein is a CTV effector that negatively affects virus pathogenicity and suggest that N. benthamiana recognizes p33 to activate the host immune response to restrict CTV into the phloem tissue and minimize the disease syndrome.
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Affiliation(s)
- Yong-Duo Sun
- Plant Pathology Department, University of Florida, Gainesville, FL, 32611, USA
- Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL, 32611, USA
| | - Svetlana Y Folimonova
- Plant Pathology Department, University of Florida, Gainesville, FL, 32611, USA
- Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL, 32611, USA
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Gómez‐Muñoz N, Velázquez K, Vives MC, Ruiz‐Ruiz S, Pina JA, Flores R, Moreno P, Guerri J. The resistance of sour orange to Citrus tristeza virus is mediated by both the salicylic acid and RNA silencing defence pathways. MOLECULAR PLANT PATHOLOGY 2017; 18:1253-1266. [PMID: 27588892 PMCID: PMC6638288 DOI: 10.1111/mpp.12488] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Revised: 08/26/2016] [Accepted: 08/30/2016] [Indexed: 05/08/2023]
Abstract
Citrus tristeza virus (CTV) induces in the field the decline and death of citrus varieties grafted on sour orange (SO) rootstock, which has forced the use of alternative decline-tolerant rootstocks in affected countries, despite the highly desirable agronomic features of the SO rootstock. Declining citrus plants display phloem necrosis below the bud union. In addition, SO is minimally susceptible to CTV compared with other citrus varieties, suggesting partial resistance of SO to CTV. Here, by silencing different citrus genes with a Citrus leaf blotch virus-based vector, we have examined the implication of the RNA silencing and salicylic acid (SA) defence pathways in the resistance of SO to CTV. Silencing of the genes RDR1, NPR1 and DCL2/DCL4, associated with these defence pathways, enhanced virus spread and accumulation in SO plants in comparison with non-silenced controls, whereas silencing of the genes NPR3/NPR4, associated with the hypersensitive response, produced a slight decrease in CTV accumulation and reduced stunting of SO grafted on CTV-infected rough lemon plants. We also found that the CTV RNA silencing suppressors p20 and p23 also suppress the SA signalling defence, with the suppressor activity being higher in the most virulent isolates.
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Affiliation(s)
- Neus Gómez‐Muñoz
- Instituto Valenciano de Investigaciones Agrarias (IVIA)Centro de Protección Vegetal y BiotecnologíaMoncada, Valencia46113Spain
| | - Karelia Velázquez
- Instituto Valenciano de Investigaciones Agrarias (IVIA)Centro de Protección Vegetal y BiotecnologíaMoncada, Valencia46113Spain
| | - María Carmen Vives
- Instituto Valenciano de Investigaciones Agrarias (IVIA)Centro de Protección Vegetal y BiotecnologíaMoncada, Valencia46113Spain
| | - Susana Ruiz‐Ruiz
- Instituto Valenciano de Investigaciones Agrarias (IVIA)Centro de Protección Vegetal y BiotecnologíaMoncada, Valencia46113Spain
| | - José Antonio Pina
- Instituto Valenciano de Investigaciones Agrarias (IVIA)Centro de Protección Vegetal y BiotecnologíaMoncada, Valencia46113Spain
| | - Ricardo Flores
- Instituto de Biología Molecular y Celular de Plantas (UPV‐CSIC), Universidad Politécnica de Valencia, Avenida de los NaranjosValencia46022Spain
| | - Pedro Moreno
- Instituto Valenciano de Investigaciones Agrarias (IVIA)Centro de Protección Vegetal y BiotecnologíaMoncada, Valencia46113Spain
| | - José Guerri
- Instituto Valenciano de Investigaciones Agrarias (IVIA)Centro de Protección Vegetal y BiotecnologíaMoncada, Valencia46113Spain
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Visser M, Cook G, Burger JT, Maree HJ. In silico analysis of the grapefruit sRNAome, transcriptome and gene regulation in response to CTV-CDVd co-infection. Virol J 2017; 14:200. [PMID: 29058618 PMCID: PMC5651572 DOI: 10.1186/s12985-017-0871-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2017] [Accepted: 10/16/2017] [Indexed: 01/15/2023] Open
Abstract
BACKGROUND Small RNA (sRNA) associated gene regulation has been shown to play a significant role during plant-pathogen interaction. In commercial citrus orchards co-infection of Citrus tristeza virus (CTV) and viroids occur naturally. METHODS A next-generation sequencing-based approach was used to study the sRNA and transcriptional response in grapefruit to the co-infection of CTV and Citrus dwarfing viroid. RESULTS The co-infection resulted in a difference in the expression of a number of sRNA species when comparing healthy and infected plants; the majority of these were derived from transcripts processed in a phased manner. Several RNA transcripts were also differentially expressed, including transcripts derived from two genes, predicted to be under the regulation of sRNAs. These genes are involved in plant hormone systems; one in the abscisic acid, and the other in the cytokinin regulatory pathway. Additional analysis of virus- and viroid-derived small-interfering RNAs (siRNAs) showed areas on the pathogen genomes associated with increased siRNA synthesis. Most interestingly, the starting position of the p23 silencing suppressor's sub-genomic RNA generated a siRNA hotspot on the CTV genome. CONCLUSIONS This study showed the involvement of various genes, as well as endogenous and exogenous RNA-derived sRNA species in the plant-defence response. The results highlighted the role of sRNA-directed plant hormone regulation during biotic stress, as well as a counter-response of plants to virus suppressors of RNA-silencing.
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Affiliation(s)
- Marike Visser
- Department of Genetics, Stellenbosch University, Stellenbosch, South Africa
| | - Glynnis Cook
- Department of Genetics, Stellenbosch University, Stellenbosch, South Africa
- Citrus Research International, Nelspruit, South Africa
| | - Johan T. Burger
- Department of Genetics, Stellenbosch University, Stellenbosch, South Africa
| | - Hans J. Maree
- Department of Genetics, Stellenbosch University, Stellenbosch, South Africa
- Agricultural Research Council, Infruitec-Nietvoorbij: Institute for Deciduous Fruit, Vines and Wine, Stellenbosch, South Africa
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Nwugo CC, Doud MS, Duan YP, Lin H. Proteomics analysis reveals novel host molecular mechanisms associated with thermotherapy of 'Ca. Liberibacter asiaticus'-infected citrus plants. BMC PLANT BIOLOGY 2016; 16:253. [PMID: 27842496 PMCID: PMC5109811 DOI: 10.1186/s12870-016-0942-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Accepted: 11/02/2016] [Indexed: 05/22/2023]
Abstract
BACKGROUND Citrus Huanglongbing (HLB), which is linked to the bacterial pathogen 'Ca. Liberibacter asiaticus' (Las), is the most devastating disease of citrus plants, and longer-term control measures via breeding or genetic engineering have been unwieldy because all cultivated citrus species are susceptible to the disease. However, the degree of susceptibility varies among citrus species, which has prompted efforts to identify potential Las resistance/tolerance-related genes in citrus plants for application in breeding or genetic engineering programs. Plant exposure to one form of stress has been shown to serendipitously induce innate resistance to other forms of stress and a recent study showed that continuous heat treatment (40 to 42 °C) reduced Las titer and HLB-associated symptoms in citrus seedlings. The goal of the present study was to apply comparative proteomics analysis via 2-DE and mass spectrometry to elucidate the molecular processes associated with heat-induced mitigation of HLB in citrus plants. Healthy or Las-infected citrus grapefruit plants were exposed to room temperature or to continuous heat treatment of 40 °C for 6 days. RESULTS An exhaustive total protein extraction process facilitated the identification of 107 differentially-expressed proteins in response to Las and/or heat treatment, which included a strong up-regulation of chaperones including small (23.6, 18.5 and 17.9 kDa) heat shock proteins, a HSP70-like protein and a ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO)-binding 60 kDa chaperonin, particularly in response to heat treatment. Other proteins that were generally down-regulated due to Las infection but up-regulated in response to heat treatment include RuBisCO activase, chlorophyll a/b binding protein, glucosidase II beta subunit-like protein, a putative lipoxygenase protein, a ferritin-like protein, and a glutathione S-transferase. CONCLUSIONS The differentially-expressed proteins identified in this study highlights a premier characterization of the molecular mechanisms potentially involved in the reversal of Las-induced pathogenicity processes in citrus plants and are hence proposed targets for application towards the development of cisgenic Las-resistant/tolerant citrus plants.
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Affiliation(s)
- Chika C. Nwugo
- USDA, Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier, 93648 CA USA
| | - Melissa S. Doud
- USDA, Agricultural Research Service, U.S. Horticultural Research Laboratory, Fort Pierce, 34945 FL USA
| | - Yong-ping Duan
- USDA, Agricultural Research Service, U.S. Horticultural Research Laboratory, Fort Pierce, 34945 FL USA
| | - Hong Lin
- USDA, Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier, 93648 CA USA
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