1
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Jiménez-Guerrero I, Sonawane M, Eckshtain-Levi N, Tuang ZK, da Silva GM, Pérez-Montaño F, Leibman-Markus M, Gupta R, Noda-Garcia L, Bar M, Burdman S. Natural variation in a short region of the Acidovorax citrulli type III-secreted effector AopW1 is associated with differences in cytotoxicity and host adaptation. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2024; 117:516-540. [PMID: 37864805 DOI: 10.1111/tpj.16507] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Revised: 10/03/2023] [Accepted: 10/04/2023] [Indexed: 10/23/2023]
Abstract
Bacterial fruit blotch, caused by Acidovorax citrulli, is a serious disease of melon and watermelon. The strains of the pathogen belong to two major genetic groups: group I strains are strongly associated with melon, while group II strains are more aggressive on watermelon. A. citrulli secretes many protein effectors to the host cell via the type III secretion system. Here we characterized AopW1, an effector that shares similarity to the actin cytoskeleton-disrupting effector HopW1 of Pseudomonas syringae and with effectors from other plant-pathogenic bacterial species. AopW1 has a highly variable region (HVR) within amino acid positions 147 to 192, showing 14 amino acid differences between group I and II variants. We show that group I AopW1 is more toxic to yeast and Nicotiana benthamiana cells than group II AopW1, having stronger actin filament disruption activity, and increased ability to induce cell death and reduce callose deposition. We further demonstrated the importance of some amino acid positions within the HVR for AopW1 cytotoxicity. Cellular analyses revealed that AopW1 also localizes to the endoplasmic reticulum, chloroplasts, and plant endosomes. We also show that overexpression of the endosome-associated protein EHD1 attenuates AopW1-induced cell death and increases defense responses. Finally, we show that sequence variation in AopW1 plays a significant role in the adaptation of group I and II strains to their preferred hosts, melon and watermelon, respectively. This study provides new insights into the HopW1 family of bacterial effectors and provides first evidence on the involvement of EHD1 in response to biotic stress.
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Affiliation(s)
- Irene Jiménez-Guerrero
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, Institute of Environmental Sciences, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Monica Sonawane
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, Institute of Environmental Sciences, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Noam Eckshtain-Levi
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, Institute of Environmental Sciences, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Za Khai Tuang
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, Institute of Environmental Sciences, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Gustavo Mateus da Silva
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, Institute of Environmental Sciences, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Francisco Pérez-Montaño
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, Institute of Environmental Sciences, The Hebrew University of Jerusalem, Rehovot, Israel
- Department of Microbiology, University of Seville, Seville, Spain
| | - Meirav Leibman-Markus
- Department of Plant Pathology and Weed Research, Agricultural Research Organization, The Volcani Institute, Bet Dagan, Israel
| | - Rupali Gupta
- Department of Plant Pathology and Weed Research, Agricultural Research Organization, The Volcani Institute, Bet Dagan, Israel
| | - Lianet Noda-Garcia
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, Institute of Environmental Sciences, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Maya Bar
- Department of Plant Pathology and Weed Research, Agricultural Research Organization, The Volcani Institute, Bet Dagan, Israel
| | - Saul Burdman
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, Institute of Environmental Sciences, The Hebrew University of Jerusalem, Rehovot, Israel
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2
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Zou H, Ding Y, Shang J, Ma C, Li J, Yang Y, Cui X, Zhang J, Ji G, Wei Y. Isolation, characterization, and genomic analysis of a novel bacteriophage MA9V-1 infecting Chryseobacterium indologenes: a pathogen of Panax notoginseng root rot. Front Microbiol 2023; 14:1251211. [PMID: 37779709 PMCID: PMC10537231 DOI: 10.3389/fmicb.2023.1251211] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2023] [Accepted: 08/21/2023] [Indexed: 10/03/2023] Open
Abstract
Chryseobacterium indologenes is one of the primary causative agents of root rot of Panax notoginseng, which significantly affected plant growth and caused economic losses. With the increasing incidence of antibiotic-resistant bacterial phytopathogens, phage therapy has been garnered renewed attention in treating pathogenic bacteria. However, the therapeutic potential of phage therapy on root rot of P. notoginseng has not been evaluated. In this study, we isolated a novel lytic phage MA9V-1 infecting C. indologenes MA9 from sewage and monitored the formation of clear and round plaques with a diameter of approximately 0.5-1.5 mm. Phage MA9V-1 exhibited rapid absorption (>75% in 8 min), a latency period of 20 min, and a burst size of 10 particles per cell. Transmission electron microscopy indicated that the phage MA9V-1 is a new myovirus hosting C. indologenes MA9. Sequencing of phage genomes revealed that phage MA9V-1 contained a linear double-stranded DNA genome of 213,507 bp with 263 predicted open reading frames, including phage structure, host lysing, and DNA polymerase/helicase but no genes of tRNA, virulence, and antibiotic resistance. Our proteomic tree and genomic analysis revealed that phage MA9V-1 shares identity with Sphingomonas phage PAU and Tenacibaculum phage PTm1; however, they also showed apparent differences. Further systemic evaluation using phage therapy experiments on P. notoginseng suggested that phage MA9V-1 can be a potential candidate for effectively controlling C. indologenes MA9 infection. Thus, we have presented a novel approach to solving root rot in P. notoginseng.
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Affiliation(s)
- He Zou
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
| | - Yafang Ding
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
| | - Junjie Shang
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
| | - Chunlan Ma
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
| | - Jinhua Li
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
| | - Ye Yang
- Key Laboratory of Sustainable Development and Utilization of Panax notoginseng Resources in Yunnan Province, Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
| | - Xiuming Cui
- Key Laboratory of Sustainable Development and Utilization of Panax notoginseng Resources in Yunnan Province, Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
| | - Jinhao Zhang
- State Key Laboratory for Conservation and Utilization of Bio-resources in Yunnan, Yunnan Agricultural University, Kunming, Yunnan, China
| | - Guanghai Ji
- State Key Laboratory for Conservation and Utilization of Bio-resources in Yunnan, Yunnan Agricultural University, Kunming, Yunnan, China
| | - Yunlin Wei
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
- Key Laboratory of Sustainable Development and Utilization of Panax notoginseng Resources in Yunnan Province, Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
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3
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Kan Y, Zhang Y, Lin W, Dong T. Differential plant cell responses to Acidovorax citrulli T3SS and T6SS reveal an effective strategy for controlling plant-associated pathogens. mBio 2023; 14:e0045923. [PMID: 37288971 PMCID: PMC10470598 DOI: 10.1128/mbio.00459-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Accepted: 05/03/2023] [Indexed: 06/09/2023] Open
Abstract
Acidovorax citrulli is a gram-negative plant pathogen that employs the type Ⅲ secretion system (T3SS) to infect cucurbit crops and cause bacterial fruit blotch. This bacterium also possesses an active type Ⅵ secretion system (T6SS) with strong antibacterial and antifungal activities. However, how plant cells respond to these two secretion systems and whether there is any cross talk between T3SS and T6SS during infection remain unknown. Here, we employ transcriptomic analysis to compare cellular responses to the T3SS and the T6SS during in planta infection and report distinctive effects on multiple pathways. The T3SS-mediated differentially expressed genes were enriched in the pathways of phenylpropanoid biosynthesis, plant-pathogen interaction, MAPK signaling pathway, and glutathione metabolism, while the T6SS uniquely affected genes were related to photosynthesis. The T6SS does not contribute to the in planta virulence of A. citrulli but is critical for the survival of the bacterium when mixed with watermelon phyllosphere bacteria. In addition, T3SS-mediated virulence is independent of the T6SS, and the inactivation of the T3SS does not affect the T6SS-mediated competition against a diverse set of bacterial pathogens that commonly contaminate edible plants or directly infect plants. A T6SS-active T3SS-null mutant (Acav) could inhibit the growth of Xanthomonas oryzae pv. oryzae significantly both in vitro and in vivo and also reduce symptoms of rice bacterial blight. In conclusion, our data demonstrate the T6SS in A. citrulli is nonpathogenic to the plant host and can be harnessed as a pathogen killer against plant-associated bacteria. IMPORTANCE Chemical pesticides are widely used to protect crops from various pathogens. Still, their extensive use has led to severe consequences, including drug resistance and environmental contamination. Here, we show that an engineered T6SS-active, but avirulent mutant of Acidovorax citrulli has strong inhibition capabilities against several pathogenic bacteria, demonstrating an effective strategy that is an alternative to chemical pesticides for sustainable agricultural practices.
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Affiliation(s)
- Yumin Kan
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Yanjie Zhang
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Wenhui Lin
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Tao Dong
- Department of Immunology and Microbiology, School of Life Sciences, Southern University of Science and Technology, Shenzhen, Guangdong, China
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4
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Qiao P, Zhao M, Guan W, Walcott R, Ye Y, Yang Y, Zhao T. A putative multi-sensor hybrid histidine kinase, BarA Ac , inhibits the expression of the type III secretion system regulator HrpG in Acidovorax citrulli. Front Microbiol 2022; 13:1064577. [PMID: 36532489 PMCID: PMC9748350 DOI: 10.3389/fmicb.2022.1064577] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2022] [Accepted: 11/14/2022] [Indexed: 07/30/2023] Open
Abstract
Bacterial fruit blotch (BFB), caused by Acidovorax citrulli, severely damages watermelon, melon, and other cucurbit crops worldwide. Although many virulence determinants have been identified in A. citrulli, including swimming motility, twitching motility, biofilm formation, and the type III secretion system (T3SS), research on their regulation is lacking. To study virulence regulation mechanisms, we found a putative histidine kinase BarA Ac that may be related to the T3SS regulator HrpG in A. citrulli. We deleted and characterized barAAc (Aave_2063) in A. citrulli Aac5 strain. Compared to the wild-type Aac5, virulence and early proliferation of barAAc mutant in host watermelon cotyledons were significantly increased, and induction of hypersensitive response in non-host tobacco was accelerated, while biofilm formation and swimming motility were significantly reduced. In addition, the transcriptomic analysis revealed that the expression of many T3SS-related genes was upregulated in the ΔbarAAc deletion mutant when cultured in KB medium. Meanwhile, the ΔbarAAc deletion mutant showed increased accumulation of the T3SS regulator HrpG in KB medium, which may account for the increased deployment of T3SS. This suggests that the putative histidine kinase BarA Ac is able to repress the T3SS expression by inhibiting HrpG in the KB medium, which appears to be important for rational energy allocation. In summary, our research provides further understanding of the regulatory network of A. citrulli virulence.
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Affiliation(s)
- Pei Qiao
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Mei Zhao
- Department of Plant Pathology, College of Plant Protection, China Agricultural University, Beijing, China
- Department of Plant Pathology, University of Georgia, Athens, GA, United States
| | - Wei Guan
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Ron Walcott
- Department of Plant Pathology, University of Georgia, Athens, GA, United States
| | - Yunfeng Ye
- Horticultural Research Institute, Guangxi Academy of Agricultural Sciences, Nanning, China
| | - Yuwen Yang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Tingchang Zhao
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
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5
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Acidovorax citrulli Effector AopV Suppresses Plant Immunity and Interacts with Aromatic Dehydratase ADT6 in Watermelon. Int J Mol Sci 2022; 23:ijms231911719. [PMID: 36233021 PMCID: PMC9570411 DOI: 10.3390/ijms231911719] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2022] [Revised: 09/25/2022] [Accepted: 09/26/2022] [Indexed: 11/17/2022] Open
Abstract
Bacterial fruit blotch (BFB) is a disease of cucurbit plants caused by Acidovorax citrulli. Although A. citrulli has great destructive potential, the molecular mechanisms of pathogenicity of A. citrulli are not clear, particularly with regard to its type III secreted effectors. In this study, we characterized the type III secreted effector protein, AopV, from A. citrulli strain Aac5. We show that AopV significantly inhibits reactive oxygen species and the expression of PTI marker genes, and helps the growth of Pseudomonas syringae D36E in Nicotiana benthamiana. In addition, we found that the aromatic dehydratase ADT6 from watermelon was a target of AopV. AopV interacts with ADT6 in vivo and in vitro. Subcellular localization indicated ADT6 and AopV were co-located at the cell membrane. Together, our results reveal that AopV suppresses plant immunity and targets ADT6 in the cell membrane. These findings provide an new characterization of the molecular interaction of A. citrulli effector protein AopV with host cells.
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6
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Wang J, Liu J, Zhao Y, Sun M, Yu G, Fan J, Tian Y, Hu B. OxyR contributes to virulence of Acidovorax citrulli by regulating anti-oxidative stress and expression of flagellin FliC and type IV pili PilA. Front Microbiol 2022; 13:977281. [PMID: 36204623 PMCID: PMC9530317 DOI: 10.3389/fmicb.2022.977281] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Accepted: 08/31/2022] [Indexed: 11/25/2022] Open
Abstract
In many bacteria, OxyR acts as a transcriptional regulator that facilitates infection via degrading hydrogen peroxide (H2O2) generated by the host defense response. Previous studies showed that OxyR also plays an important role in regulating biofilm formation, cell motility, pili relate-genes expression, and surface polysaccharide production. However, the role of OxyR has not been determined in Acidovorax citrulli strain xjl12. In the current study, the qRT-PCR and western blot assays revealed that the expression level of oxyR was significantly induced by H2O2. The oxyR deletion mutant of A. citrulli was significantly impaired bacterial tolerance to oxidative stress and reduced catalase (CAT) activity. In addition, oxyR mutant resulted in reduced swimming motility, twitching motility, biofilm formation, virulence, and bacterial growth in planta by significantly affecting flagellin and type IV pili-related gene (fliC and pilA) expression. The qRT-PCR assays and western blot revealed that OxyR positively regulated the expression of fliC and pilA. Furthermore, bacterial one-hybrid assay demonstrated that OxyR directly affected pilA and fliC promoter. Through bacterial two-hybrid assay, it was found that OxyR can directly interact with PilA and FliC. These results suggest that OxyR plays a major role in the regulating of a variety of virulence traits, and provide a foundation for future research on the global effects of OxyR in A. citrulli.
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Affiliation(s)
- Jianan Wang
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Nanjing Agricultural University, Nanjing, China
| | - Jun Liu
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Nanjing Agricultural University, Nanjing, China
- Institute of Plant Protection and Soil Fertilizer, Hubei Academy of Agricultural Sciences, Wuhan, China
| | - Yuqiang Zhao
- Institute of Botany, Jiangsu Province and Chinese Academy of Sciences (Nanjing Botanical Garden Mem. Sun Yat-Sen), Nanjing, China
| | - Minghui Sun
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Nanjing Agricultural University, Nanjing, China
| | - Guixu Yu
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Nanjing Agricultural University, Nanjing, China
| | - Jiaqin Fan
- Laboratory of Bacteriology, Department of Plant Pathology, Nanjing Agricultural University, Nanjing, China
| | - Yanli Tian
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Nanjing Agricultural University, Nanjing, China
- *Correspondence: Yanli Tian,
| | - Baishi Hu
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Nanjing Agricultural University, Nanjing, China
- Baishi Hu,
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Wang T, Huang Q, An X, Yang Y, Guan W, Zhao T. Type III secretion system genes hrcJ and hrpE affect virulence, hypersensitive response and biofilm formation of group II strains of Acidovorax citrulli. FRONTIERS IN SUSTAINABLE FOOD SYSTEMS 2022. [DOI: 10.3389/fsufs.2022.995894] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Bacterial fruit blotch (BFB) caused by Acidovorax citrulli is a worldwide threat to watermelon and melon production. The type III secretion system (T3SS) plays an important role in the virulence of A. citrulli in its host plants and to induce hypersensitive response (HR) in its non-host plants. Little is known, however, about the contribution of the T3SS to biofilm formation in A. citrulli. We mutated two T3SS-related genes hrcJ and hrpE, respectively, and compared the mutants with their wild-type strain Aac-5 of A. citrulli, and their complementation strains on virulence, HR, and biofilm formation. Both mutants significantly reduced virulence in watermelon and melon seedlings and their ability to induce HR in tobacco leaves. Such reduction phenotypes were significantly recovered to the wild-type level, when the mutant strains were complemented with the wild-type hrcJ and hrpE genes. Interestingly, the two T3SS-related gene mutants also displayed enhanced ability to form biofilm, suggesting a different role of biofilm in the virulence of the group II stains of A. citrulli.
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Rosenberg T, Jiménez-Guerrero I, Tamir-Ariel D, Yarnitzky T, Burdman S. The GDSL-Lipolytic Enzyme Lip1 Is Required for Full Virulence of the Cucurbit Pathogenic Bacterium Acidovorax citrulli. Microorganisms 2022; 10:microorganisms10051016. [PMID: 35630458 PMCID: PMC9147443 DOI: 10.3390/microorganisms10051016] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2022] [Revised: 05/04/2022] [Accepted: 05/09/2022] [Indexed: 02/01/2023] Open
Abstract
Bacterial fruit blotch caused by Acidovoraxcitrulli is a serious disease of cucurbit crops. Here we report characterization of a mutant strain of A. citrulli M6 defective in lip1, a gene encoding a lipolytic enzyme. The M6-lip1- mutant was detected in a mutant library screen aimed at identifying M6 mutants with altered levels of twitching motility. In this screen M6-lip1- was the only mutant that showed significantly larger twitching motility haloes around colonies than wild-type M6. Sequence analyses indicated that lip1 encodes a member of the GDSL family of secreted lipolytic enzymes. In line with this finding, lipolytic assays showed that the supernatants of M6-lip1- had lower lipolytic activity as compared with those of wild-type M6 and a lip1-complemented strain. The mutant was also affected in swimming motility and had compromised virulence on melon seedlings and on Nicotiana benthamiana leaves relative to wild-type and complemented strains. Lip1 contains a predicted N-terminal signal sequence for type II secretion. Evidence from our study confirms Lip1 is indeed secreted in a type II secretion-dependent manner, and this is required for full virulence of A. citrulli. To the best of our knowledge this is the first study reporting contribution of lipolytic activity to virulence of a plant-pathogenic Acidovorax species.
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Affiliation(s)
- Tally Rosenberg
- Department of Plant Pathology and Microbiology, Institute of Environmental Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 7610001, Israel; (T.R.); (I.J.-G.); (D.T.-A.); (T.Y.)
| | - Irene Jiménez-Guerrero
- Department of Plant Pathology and Microbiology, Institute of Environmental Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 7610001, Israel; (T.R.); (I.J.-G.); (D.T.-A.); (T.Y.)
- Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla, 41012 Sevilla, Spain
| | - Dafna Tamir-Ariel
- Department of Plant Pathology and Microbiology, Institute of Environmental Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 7610001, Israel; (T.R.); (I.J.-G.); (D.T.-A.); (T.Y.)
| | - Tali Yarnitzky
- Department of Plant Pathology and Microbiology, Institute of Environmental Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 7610001, Israel; (T.R.); (I.J.-G.); (D.T.-A.); (T.Y.)
| | - Saul Burdman
- Department of Plant Pathology and Microbiology, Institute of Environmental Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 7610001, Israel; (T.R.); (I.J.-G.); (D.T.-A.); (T.Y.)
- Correspondence: ; Tel.: +972-8-9489369
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Pei T, Kan Y, Wang Z, Tang M, Li H, Yan S, Cui Y, Zheng H, Luo H, Liang X, Dong T. Delivery of an Rhs-family nuclease effector reveals direct penetration of the gram-positive cell envelope by a type VI secretion system in Acidovorax citrulli. MLIFE 2022; 1:66-78. [PMID: 38818323 PMCID: PMC10989746 DOI: 10.1002/mlf2.12007] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/06/2021] [Accepted: 12/16/2021] [Indexed: 06/01/2024]
Abstract
The type VI secretion system (T6SS) is a double-tubular nanomachine widely found in gram-negative bacteria. Its spear-like Hcp tube is capable of penetrating a neighboring cell for cytosol-to-cytosol protein delivery. However, gram-positive bacteria have been considered impenetrable to such T6SS action. Here we report that the T6SS of a plant pathogen, Acidovorax citrulli (AC), could deliver an Rhs-family nuclease effector RhsB to kill not only gram-negative but also gram-positive bacteria. Using bioinformatic, biochemical, and genetic assays, we systematically identified T6SS-secreted effectors and determined that RhsB is a crucial antibacterial effector. RhsB contains an N-terminal PAAR domain, a middle Rhs domain, and an unknown C-terminal domain. RhsB is subject to self-cleavage at both its N- and C-terminal domains and its secretion requires the upstream-encoded chaperone EagT2 and VgrG3. The toxic C-terminus of RhsB exhibits DNase activities and such toxicity is neutralized by either of the two downstream immunity proteins, RimB1 and RimB2. Deletion of rhsB significantly impairs the ability of killing Bacillus subtilis while ectopic expression of immunity proteins RimB1 or RimB2 confers protection. We demonstrate that the AC T6SS not only can effectively outcompete Escherichia coli and B. subtilis in planta but also is highly potent in killing other bacterial and fungal species. Collectively, these findings highlight the greatly expanded capabilities of T6SS in modulating microbiome compositions in complex environments.
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Affiliation(s)
- Tong‐Tong Pei
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic & Developmental Sciences, School of Life Sciences and BiotechnologyShanghai Jiao Tong UniversityShanghaiChina
| | - Yumin Kan
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic & Developmental Sciences, School of Life Sciences and BiotechnologyShanghai Jiao Tong UniversityShanghaiChina
| | - Zeng‐Hang Wang
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic & Developmental Sciences, School of Life Sciences and BiotechnologyShanghai Jiao Tong UniversityShanghaiChina
| | - Ming‐Xuan Tang
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic & Developmental Sciences, School of Life Sciences and BiotechnologyShanghai Jiao Tong UniversityShanghaiChina
| | - Hao Li
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic & Developmental Sciences, School of Life Sciences and BiotechnologyShanghai Jiao Tong UniversityShanghaiChina
| | - Shuangquan Yan
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic & Developmental Sciences, School of Life Sciences and BiotechnologyShanghai Jiao Tong UniversityShanghaiChina
| | - Yang Cui
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic & Developmental Sciences, School of Life Sciences and BiotechnologyShanghai Jiao Tong UniversityShanghaiChina
| | - Hao‐Yu Zheng
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic & Developmental Sciences, School of Life Sciences and BiotechnologyShanghai Jiao Tong UniversityShanghaiChina
| | - Han Luo
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic & Developmental Sciences, School of Life Sciences and BiotechnologyShanghai Jiao Tong UniversityShanghaiChina
| | - Xiaoye Liang
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic & Developmental Sciences, School of Life Sciences and BiotechnologyShanghai Jiao Tong UniversityShanghaiChina
| | - Tao Dong
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic & Developmental Sciences, School of Life Sciences and BiotechnologyShanghai Jiao Tong UniversityShanghaiChina
- Department of Immunology and MicrobiologySchool of Life Sciences, Southern University of Science and TechnologyGuangdongChina
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10
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Gašić K, Obradović M, Kuzmanović N, Zlatković N, Ivanović M, Ristić D, Obradović A. Isolation, Characterization and Draft Genome Analysis of Bacteriophages Infecting Acidovorax citrulli. Front Microbiol 2022; 12:803789. [PMID: 35185829 PMCID: PMC8851203 DOI: 10.3389/fmicb.2021.803789] [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: 10/28/2021] [Accepted: 12/06/2021] [Indexed: 12/05/2022] Open
Abstract
Bacterial fruit blotch and seedling blight, caused by Acidovorax citrulli, is one of the most destructive diseases of melon and watermelon in many countries. Pathogen-free seed and cultural practices are major pillars of the disease control. However, use of bacteriophages as natural biocontrol agents might also contribute to the disease management. Therefore, we isolated 12 bacteriophages specific to A. citrulli, from phyllosphere and rhizosphere of diseased watermelon plants. The phage strains were characterized based on their host range, plaque and virion morphology, thermal inactivation point, adsorption rate, one step growth curve, restriction fragment length polymorphism (RFLP), and genomic analysis. Transmission electron microscopy of three phage strains indicated that they belong to the order Caudovirales, family Siphoviridae. All phages lysed 30 out of 32 tested A. citrulli strains isolated in Serbia, and did not lyse other less related bacterial species. They produced clear plaques, 2 mm in diameter, on bacterial lawns of different A. citrulli strains after 24 h of incubation. The thermal inactivation point was 66 or 67°C. They were stable at pH 5–9, but were sensitive to chloroform and inactivated in either 5 or 10 min exposure to ultraviolet (UV) light. RFLP analysis using EcoRI, BsmI and BamHI enzymes did not show genetic differences among the tested phages. Adsorption rate and one step growth curve were determined for the Acidovorax phage ACF1. Draft genome sequence of the ACF1 phage was 59.377 bp in size, with guanine-cytosine (GC) content 64.5%, including 89 open reading frames. This phage shared a very high genomic identity with Acidovorax phage ACPWH, isolated in South Korea. Evaluation of systemic nature of ACF1 strain showed that it can be absorbed by roots and translocated to upper parts of watermelon plants where it survived up to 10 days.
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Affiliation(s)
- Katarina Gašić
- Institute for Plant Protection and Environment, Belgrade, Serbia
| | - Mina Obradović
- Institute of Molecular Genetics and Genetic Engineering, University of Belgrade, Belgrade, Serbia
| | - Nemanja Kuzmanović
- Federal Research Centre for Cultivated Plants, Institute for Plant Protection in Horticulture and Forests, Julius Kühn-Institut, Braunschweig, Germany
| | - Nevena Zlatković
- Institute for Plant Protection and Environment, Belgrade, Serbia
| | - Milan Ivanović
- Faculty of Agriculture, University of Belgrade, Belgrade, Serbia
| | - Danijela Ristić
- Institute for Plant Protection and Environment, Belgrade, Serbia
| | - Aleksa Obradović
- Faculty of Agriculture, University of Belgrade, Belgrade, Serbia
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11
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Wang Y, Zhao Y, Xia L, Chen L, Liao Y, Chen B, Liu Y, Gong W, Tian Y, Hu B. yggS Encoding Pyridoxal 5'-Phosphate Binding Protein Is Required for Acidovorax citrulli Virulence. Front Microbiol 2022; 12:783862. [PMID: 35087487 PMCID: PMC8787154 DOI: 10.3389/fmicb.2021.783862] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Accepted: 12/06/2021] [Indexed: 11/26/2022] Open
Abstract
Bacterial fruit blotch, caused by seed-borne pathogen Acidovorax citrulli, poses a serious threat to the production of cucurbits globally. Although the disease can cause substantial economic losses, limited information is available about the molecular mechanisms of virulence. This study identified that, a random transposon insertion mutant impaired in the ability to elicit a hypersensitive response on tobacco. The disrupted gene in this mutant was determined to be Aave_0638, which is predicted to encode a YggS family pyridoxal phosphate-dependent enzyme. YggS is a highly conserved protein among multiple organisms, and is responsible for maintaining the homeostasis of pyridoxal 5′-phosphate and amino acids in cells. yggS deletion mutant of A. citrulli strain XjL12 displayed attenuated virulence, delayed hypersensitive response, less tolerance to H2O2 and pyridoxine, increased sensitivity to antibiotic β-chloro-D-alanine, and reduced swimming. In addition, RNA-Seq analysis demonstrated that yggS was involved in regulating the expression of certain pathogenicity-associated genes related to secretion, motility, quorum sensing and oxidative stress response. Importantly, YggS significantly affected type III secretion system and its effectors in vitro. Collectively, our results suggest that YggS is indispensable for A.citrulli virulence and expands the role of YggS in the biological processes.
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Affiliation(s)
- Yuanjie Wang
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing Agricultural University, Nanjing, China
| | - Yuqiang Zhao
- Institute of Botany, Jiangsu Province and Chinese Academy of Sciences (Nanjing Botanical Garden Mem. Sun Yat-sen), Nanjing, China
| | - Liming Xia
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing Agricultural University, Nanjing, China
| | - Lin Chen
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing Agricultural University, Nanjing, China
| | - Yajie Liao
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing Agricultural University, Nanjing, China
| | - Baohui Chen
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing Agricultural University, Nanjing, China
| | - Yiyang Liu
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing Agricultural University, Nanjing, China
| | - Weirong Gong
- Plant Protection and Quarantine Station of Province, Nanjing, China
| | - Yanli Tian
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing Agricultural University, Nanjing, China
| | - Baishi Hu
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing Agricultural University, Nanjing, China
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12
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Mijatović J, Severns PM, Kemerait RC, Walcott RR, Kvitko BH. Patterns of Seed-to-Seedling Transmission of Xanthomonas citri pv. malvacearum, the Causal Agent of Cotton Bacterial Blight. PHYTOPATHOLOGY 2021; 111:2176-2184. [PMID: 34032522 DOI: 10.1094/phyto-02-21-0057-r] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Cotton bacterial blight (CBB), caused by Xanthomonas citri pv. malvacearum, was a major disease of cotton in the United States in the early part of the twentieth century. The reemergence of CBB revealed many gaps in our understanding of this important disease. In this study, we employed a wild-type (WT) field isolate of X. citri pv. malvacearum from Georgia (U.S.A.) to generate a nonpathogenic hrcV mutant lacking a functional type-III secretion system (T3SS-). We tagged the WT and T3SS- strains with an auto-bioluminescent Tn7 reporter and compared colonization patterns of CBB-susceptible and CBB-resistant cotton seedlings using macroscopic image analysis and bacterial load enumeration. WT and T3SS- X. citri pv. malvacearum strains colonized cotton cotyledons of CBB-resistant and CBB-susceptible cotton cultivars. However, X. citri pv. malvacearum populations were significantly higher in CBB-susceptible seedlings inoculated with the WT strain. Additionally, WT and T3SS- X. citri pv. malvacearum strains systemically colonized true leaves, although at different rates. Finally, we observed that seed-to-seedling transmission of X. citri pv. malvacearum may involve systemic spread through the vascular tissue of cotton plants. These findings yield novel insights into potential X. citri pv. malvacearum reservoirs for CBB outbreaks.
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Affiliation(s)
- Jovana Mijatović
- Department of Plant Pathology, University of Georgia, Athens, GA 30602
| | - Paul M Severns
- Department of Plant Pathology, University of Georgia, Athens, GA 30602
| | - Robert C Kemerait
- Department of Plant Pathology, University of Georgia, Tifton, GA 31793
| | - Ron R Walcott
- Department of Plant Pathology, University of Georgia, Athens, GA 30602
| | - Brian H Kvitko
- Department of Plant Pathology, University of Georgia, Athens, GA 30602
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13
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Lee J, Heo L, Han SW. Comparative Proteomic Analysis for a Putative Pyridoxal Phosphate-Dependent Aminotransferase Required for Virulence in Acidovorax citrulli. THE PLANT PATHOLOGY JOURNAL 2021; 37:673-680. [PMID: 34897258 PMCID: PMC8666244 DOI: 10.5423/ppj.nt.09.2021.0139] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/09/2021] [Revised: 10/06/2021] [Accepted: 10/13/2021] [Indexed: 06/14/2023]
Abstract
Acidovorax citrulli (Ac) is the causative agent of bacterial fruit blotch disease in watermelon. Since resistant cultivars have not yet been developed, the virulence factors/mechanisms of Ac need to be characterized. This study reports the functions of a putative pyridoxal phosphate-dependent aminotransferase (PpdaAc) that transfers amino groups to its substrates and uses pyridoxal phosphate as a coenzyme. It was observed that a ppdaAc knockout mutant had a significantly reduced virulence in watermelon when introduced via germinated-seed inoculation as well as leaf infiltration. Comparative proteomic analysis predicted the cellular mechanisms related to PpdaAc. Apart from causing virulence, the PpdaAc may have significant roles in energy production, cell membrane, motility, chemotaxis, post-translational modifications, and iron-related mechanisms. Therefore, it is postulated that PpdaAc may possess pleiotropic effects. These results provide new insights into the functions of a previously unidentified PpdaAc in Ac.
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Affiliation(s)
| | | | - Sang-Wook Han
- Corresponding author: Phone) +82-31-670-3150, FAX) +82-2-670-8845, E-mail)
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14
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Liu Y, Zhou Y, Qiao J, Yu W, Pan X, Zhang T, Liu Y, Lu SE. Phenazine-1-carboxylic Acid Produced by Pseudomonas chlororaphis YL-1 Is Effective against Acidovorax citrulli. Microorganisms 2021; 9:microorganisms9102012. [PMID: 34683333 PMCID: PMC8541086 DOI: 10.3390/microorganisms9102012] [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: 07/21/2021] [Revised: 09/19/2021] [Accepted: 09/20/2021] [Indexed: 11/16/2022] Open
Abstract
The bacterial pathogen Acidovorax citrulli causes the destructive fruit blotch (BFB) on cucurbit plants. Pseudomonas chlororaphis YL-1 is a bacterial strain isolated from Mississippi soil and its genome harbors some antimicrobial-related gene clusters, such as phenazine, pyrrolnitrin, and pyoverdine. Here, we evaluated the antimicrobial activity of strain YL-1 as compared with its deficient mutants of antimicrobial-related genes, which were obtained using a sacB-based site-specific mutagenesis strategy. We found that only phenazine-deficient mutants ΔphzE and ΔphzF almost lost the inhibitory effects against A. citrulli in LB plates compared with the wild-type strain YL-1, and that the main antibacterial compound produced by strain YL-1 in LB medium was phenazine-1-carboxylic acid (PCA) based on the liquid chromatography-mass spectrometry (LC-MS) analysis. Gene expression analyses revealed that PCA enhanced the accumulation of reactive oxygen species (ROS) and increased the activity of catalase (CAT) in A. citrulli. The inhibition effect of PCA against A. citrulli was lowered by adding exogenous CAT. PCA significantly upregulated the transcript level of katB from 6 to 10 h, which encodes CAT that helps to protect the bacteria against oxidative stress. Collectively, the findings of this research suggest PCA is one of the key antimicrobial metabolites of bacterial strain YL-1, a promising biocontrol agent for disease management of BFB of cucurbit plants.
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Affiliation(s)
- Youzhou Liu
- Institute of Plant Protection, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China; (Y.L.); (Y.Z.); (J.Q.); (X.P.)
- Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mississippi State University, Starkville, MS 39759, USA
| | - Yaqiu Zhou
- Institute of Plant Protection, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China; (Y.L.); (Y.Z.); (J.Q.); (X.P.)
| | - Junqing Qiao
- Institute of Plant Protection, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China; (Y.L.); (Y.Z.); (J.Q.); (X.P.)
| | - Wenjie Yu
- College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China; (W.Y.); (T.Z.)
| | - Xiayan Pan
- Institute of Plant Protection, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China; (Y.L.); (Y.Z.); (J.Q.); (X.P.)
| | - Tingting Zhang
- College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China; (W.Y.); (T.Z.)
| | - Yongfeng Liu
- Institute of Plant Protection, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China; (Y.L.); (Y.Z.); (J.Q.); (X.P.)
- Correspondence: (Y.L.); (S.-E.L.)
| | - Shi-En Lu
- Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mississippi State University, Starkville, MS 39759, USA
- Correspondence: (Y.L.); (S.-E.L.)
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15
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Klomchit A, Calderin JD, Jaidee W, Watla-iad K, Brooks S. Napthoquinones from Neocosmospora sp.-Antibiotic Activity against Acidovorax citrulli, the Causative Agent of Bacterial Fruit Blotch in Watermelon and Melon. J Fungi (Basel) 2021; 7:370. [PMID: 34066879 PMCID: PMC8151544 DOI: 10.3390/jof7050370] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Revised: 05/03/2021] [Accepted: 05/05/2021] [Indexed: 11/18/2022] Open
Abstract
Bacterial fruit blotch (BFB) is a bacterial disease that devastates Cucurbitaceae crops worldwide, causing significant economic losses. Currently, there is no means to treat or control the disease. This study focused on exploring the antibacterial properties of endophytic fungi against Acidovorax citrulli (Aac), the causative agent of BFB. Based on disc diffusion, time kill and MIC microdilution broth assays, four endophytes showed promise in controlling Aac. Nonetheless, only one strain, Neocosmospora sp. MFLUCC 17-0253, reduced the severity of disease on watermelon and melon seedlings up to 80%. Structure analysis revealed production of several compounds by the fungus. Three of these secondary metabolites, including mixture of 2-methoxy-6-methyl-7-acetonyl-8-hydroxy-1,4-maphthalenedione and 5,8-dihydroxy-7-acetonyl-1,4-naphthalenedione, anhydrojavanicin, and fusarnaphthoquinones B exhibited antagonistic activity against Aac. The chemical profile data in planta experiment analyzed by LC-Q/TOF-MS suggested successful colonization of endophytic fungi in their host plant and different metabolic profiles between treated and untreated seedling. Biofilm assay also demonstrated that secondary metabolites of Neocosmospora sp. MFLUCC 17-0253 significantly inhibited biofilm development of Aac. To the best of our knowledge, secondary metabolites that provide significant growth inhibition of Aac are reported for the first time. Thus, Neocosmospora sp. MFLUCC 17-0253 possesses high potential as a biocontrol agent for BFB disease.
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Affiliation(s)
- Anthikan Klomchit
- School of Science, Mae Fah Luang University, Chiang Rai 57100, Thailand; (A.K.); (K.W.-i.)
| | - Jorge Daniel Calderin
- Department of Biochemistry, University of Illinois, Urbana-Champaign, IL 61820, USA;
| | - Wuttichai Jaidee
- Medicinal Plant Innovation Center, Mae Fah Luang University, Chiang Rai 57100, Thailand;
| | - Kanchana Watla-iad
- School of Science, Mae Fah Luang University, Chiang Rai 57100, Thailand; (A.K.); (K.W.-i.)
| | - Siraprapa Brooks
- School of Science, Mae Fah Luang University, Chiang Rai 57100, Thailand; (A.K.); (K.W.-i.)
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16
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Zhang X, Yang Y, Zhao M, Yang L, Jiang J, Walcott R, Yang S, Zhao T. Acidovorax citrulli Type III Effector AopP Suppresses Plant Immunity by Targeting the Watermelon Transcription Factor WRKY6. FRONTIERS IN PLANT SCIENCE 2020; 11:579218. [PMID: 33329640 PMCID: PMC7718035 DOI: 10.3389/fpls.2020.579218] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Accepted: 10/14/2020] [Indexed: 06/12/2023]
Abstract
Acidovorax citrulli (Ac) is the causal agent of bacterial fruit blotch (BFB), and BFB poses a threat to global watermelon production. Despite its economic importance, the molecular mechanisms underlying Ac pathogenicity and virulence are not well understood, particularly with regard to its type III secreted effectors. We identify a new effector, AopP, in Ac and confirm its secretion and translocation. AopP suppresses reactive oxygen species burst and salicylic acid (SA) content and significantly contributes to virulence. Interestingly, AopP interacts with a watermelon transcription factor, ClWRKY6, in vivo and in vitro. ClWRKY6 shows typical nuclear localization, and AopP and ClWRKY6 co-localize in the nucleus. Ac infection, SA, and the pathogen-associated molecular pattern flg22 Ac promote ClWRKY6 production, suggesting that ClWRKY6 is involved in plant immunity and SA signaling. Furthermore, ClWRKY6 positively regulates PTI and SA production when expressed in Nicotiana benthamiana. Importantly, AopP reduces ClWRKY6 mRNA and ClWRKY6 protein levels, suggesting that AopP suppresses plant immunity by targeting ClWRKY6. In summary, we identify a novel effector associated with the virulence mechanism of Ac, which interacts with the transcription factor of the natural host, watermelon. The findings of this study provide insights into the mechanisms of watermelon immune responses and may facilitate molecular breeding for bacterial fruit blotch resistance.
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Affiliation(s)
- Xiaoxiao Zhang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Yuwen Yang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Mei Zhao
- Department of Plant Pathology, University of Georgia, Athens, GA, United States
| | - Linlin Yang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Jie Jiang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Ron Walcott
- Department of Plant Pathology, University of Georgia, Athens, GA, United States
| | - Shanshan Yang
- Institute of Medicinal Plant Development, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Tingchang Zhao
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
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17
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Rahimi-Midani A, Choi TJ. Transport of Phage in Melon Plants and Inhibition of Progression of Bacterial Fruit Blotch. Viruses 2020; 12:v12040477. [PMID: 32340158 PMCID: PMC7232510 DOI: 10.3390/v12040477] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2020] [Revised: 04/20/2020] [Accepted: 04/21/2020] [Indexed: 12/13/2022] Open
Abstract
Bacterial fruit blotch (BFB) is an economically important disease in melons and watermelons for which no effective control method is available. Application of phytobacterium-infecting phage has been evaluated as an alternative means of preventing bacterial diseases in plants. Coating of seeds with bacteriophages infecting Acidovorax citrulli, the causal agent of BFB, is effective for controlling the disease, as shown in our previous study. We evaluated the transport of bacteriophage ACPWH from soil to the leaves of melon plants, and we also evaluated its effect on BFB. Leaves of melon plants were spray-inoculated with A. citrulli, and bacteriophage ACPWH was added to soil after symptoms had developed. ACPWH was detected by PCR in foliar tissue 8 h after addition to soil. DAPI-stained ACPWH accumulated at the leaf tip after 24 h. Melon treated with ACPWH showed 27% disease severity, compared to 80% for the non-treated control, indicating that ACPWH can be used to control BFB.
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18
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Guan W, Wang T, Huang Q, Tian E, Liu B, Yang Y, Zhao T. A LuxR-type regulator, AcrR, regulates flagellar assembly and contributes to virulence, motility, biofilm formation, and growth ability of Acidovorax citrulli. MOLECULAR PLANT PATHOLOGY 2020; 21:489-501. [PMID: 31943660 PMCID: PMC7060138 DOI: 10.1111/mpp.12910] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Revised: 12/05/2019] [Accepted: 12/20/2019] [Indexed: 05/26/2023]
Abstract
LuxR-type regulators regulate many bacterial processes and play important roles in bacterial motility and virulence. Acidovorax citrulli is a seedborne bacterial pathogen responsible for bacterial fruit blotch, which causes great losses in melon and watermelon worldwide. We identified a LuxR-type, nonquorum sensing-related regulator, AcrR, in the group II strain Aac-5 of A. citrulli. We found that the acrR mutant lost twitching and swimming motilities, and flagellar formation. It also showed reduced virulence, but increased biofilm formation and growth ability. Transcriptomic analysis revealed that 394 genes were differentially expressed in the acrR mutant of A. citrulli, including 33 genes involved in flagellar assembly. Our results suggest that AcrR may act as a global regulator affecting multiple important biological functions of A. citrulli.
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Affiliation(s)
- Wei Guan
- State Key Laboratory for Biology of Plant Diseases and Insect PestsInstitute of Plant ProtectionChinese Academy of Agricultural SciencesBeijingChina
| | - Tielin Wang
- State Key Laboratory Breeding Base of Dao‐di HerbsNational Resource Center for Chinese Materia MedicaChina Academy of Chinese Medical SciencesBeijingChina
| | - Qi Huang
- Floral and Nursery Plants Research UnitU.S. Department of AgricultureAgricultural Research ServiceBeltsvilleMDUSA
| | - Eryuan Tian
- State Key Laboratory for Biology of Plant Diseases and Insect PestsInstitute of Plant ProtectionChinese Academy of Agricultural SciencesBeijingChina
| | - Bo Liu
- State Key Laboratory for Biology of Plant Diseases and Insect PestsInstitute of Plant ProtectionChinese Academy of Agricultural SciencesBeijingChina
| | - Yuwen Yang
- State Key Laboratory for Biology of Plant Diseases and Insect PestsInstitute of Plant ProtectionChinese Academy of Agricultural SciencesBeijingChina
| | - Tingchang Zhao
- State Key Laboratory for Biology of Plant Diseases and Insect PestsInstitute of Plant ProtectionChinese Academy of Agricultural SciencesBeijingChina
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19
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Liu J, Tian Y, Zhao Y, Zeng R, Chen B, Hu B, Walcott RR. Ferric Uptake Regulator (FurA) is Required for Acidovorax citrulli Virulence on Watermelon. PHYTOPATHOLOGY 2019; 109:1997-2008. [PMID: 31454303 DOI: 10.1094/phyto-05-19-0172-r] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Acidovorax citrulli is the causal agent of bacterial fruit blotch, a serious threat to commercial watermelon and melon crop production worldwide. Ferric uptake regulator (Fur) is a global transcription factor that affects a number of virulence-related functions in phytopathogenic bacteria; however, the role of furA has not been determined for A. citrulli. Hence, we constructed an furA deletion mutant and a corresponding complement in the background of A. citrulli strain xlj12 to investigate the role of the gene in siderophore production, concentration of intracellular Fe2+, bacterial sensitivity to hydrogen peroxide, biofilm formation, swimming motility, hypersensitive response induction, and virulence on melon seedlings. The A. citrulli furA deletion mutant displayed increased siderophore production, intracellular Fe2+ concentration, and increased sensitivity to hydrogen peroxide. In contrast, biofilm formation, swimming motility, and virulence on melon seedlings were significantly reduced in the furA mutant. As expected, complementation of the furA deletion mutant restored all phenotypes to wild-type levels. In accordance with the phenotypic results, the expression levels of bfrA and bfrB that encode bacterioferritin, sodB that encodes iron/manganese superoxide dismutase, fliS that encodes a flagellar protein, hrcN that encodes the type III secretion system (T3SS) ATPase, and hrcC that encodes the T3SS outer membrane ring protein were significantly downregulated in the A. citrulli furA deletion mutant. In addition, the expression of feo-related genes and feoA and feoB was significantly upregulated in the furA mutant. Overall, these results indicated that, in A. citrulli, FurA contributes to the regulation of the iron balance system, and affects a variety of virulence-related traits.
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Affiliation(s)
- Jun Liu
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing Agricultural University, Nanjing 210095, China
| | - Yanli Tian
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing Agricultural University, Nanjing 210095, China
| | - Yuqiang Zhao
- Institute of Botany, Jiangsu Province and Chinese Academy of Sciences (Nanjing Botanical Garden Mem. Sun Yat-Sen), Nanjing 210014, China
| | - Rong Zeng
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing Agricultural University, Nanjing 210095, China
| | - Baohui Chen
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing Agricultural University, Nanjing 210095, China
| | - Baishi Hu
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing Agricultural University, Nanjing 210095, China
| | - Ron R Walcott
- Department of Plant Pathology, 4315 Miller Plant Sciences, the University of Georgia, Athens, GA 30602, U.S.A
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Rahimi-Midani A, Kim JO, Kim JH, Lim J, Ryu JG, Kim MK, Choi TJ. Potential use of newly isolated bacteriophage as a biocontrol against Acidovorax citrulli. Arch Microbiol 2019; 202:377-389. [DOI: 10.1007/s00203-019-01754-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2019] [Revised: 10/18/2019] [Accepted: 10/22/2019] [Indexed: 12/16/2022]
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21
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Ma YN, Chen L, Si NG, Jiang WJ, Zhou ZG, Liu JL, Zhang LQ. Identification of Benzyloxy Carbonimidoyl Dicyanide Derivatives as Novel Type III Secretion System Inhibitors via High-Throughput Screening. FRONTIERS IN PLANT SCIENCE 2019; 10:1059. [PMID: 31543889 PMCID: PMC6739442 DOI: 10.3389/fpls.2019.01059] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/15/2019] [Accepted: 08/05/2019] [Indexed: 06/10/2023]
Abstract
The type III secretion system (T3SS) in many Gram-negative bacterial pathogens is regarded as the most critical virulence determinant and an attractive target for novel anti-virulence drugs. In this study, we constructed a T3SS secretion reporter containing the β-lactamase gene fused with a signal peptide sequence of the T3SS effector gene, and established a high-throughput screening system for T3SS inhibitors in the plant pathogenic bacterium Acidovorax citrulli. From a library of 12,000 chemical compounds, we identified a series of benzyloxy carbonimidoyl dicyanide (BCD) derivatives that effectively blocked T3SS-dependent β-lactamase secretion. Substitution of halogens or nitro groups at the para-position on the benzene ring contributed to an increased inhibitory activity. One representative compound, BCD03 (3,4-dichloro-benzyloxy carbonimidoyl dicyanide), dramatically reduced pathogenicity of A. citrulli on melon seedlings, and attenuated hypersensitive responses in the non-host Nicotiana tabacum caused by pathogenic bacteria A. citrulli, Xanthomonas oryzae pv. oryzae and Pseudomonas syringae pv. tomato at sub-MIC concentrations. Western blotting assay further confirmed that BCD03 inhibited effector secretion from the above bacteria via T3SS in the liquid medium. Taken together, our data suggest that BCD derivatives act as novel inhibitors of T3SS in multiple plant bacterial pathogens.
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Affiliation(s)
- Yi-Nan Ma
- Department of Plant Pathology and MOA Key Laboratory of Pest Monitoring and Green Management, China Agricultural University, Beijing, China
| | - Liang Chen
- Department of Plant Pathology and MOA Key Laboratory of Pest Monitoring and Green Management, China Agricultural University, Beijing, China
- State Key Laboratory of the Discovery and Development of Novel Pesticide, Shenyang Sinochem Agrochemicals R&D Co., Ltd, Shenyang, China
| | - Nai-Guo Si
- State Key Laboratory of the Discovery and Development of Novel Pesticide, Shenyang Sinochem Agrochemicals R&D Co., Ltd, Shenyang, China
| | - Wen-Jun Jiang
- Department of Plant Pathology and MOA Key Laboratory of Pest Monitoring and Green Management, China Agricultural University, Beijing, China
| | - Zhi-Gang Zhou
- China-Norway Joint Lab on Fish Gut Microbiota, Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Jun-Li Liu
- State Key Laboratory of the Discovery and Development of Novel Pesticide, Shenyang Sinochem Agrochemicals R&D Co., Ltd, Shenyang, China
| | - Li-Qun Zhang
- Department of Plant Pathology and MOA Key Laboratory of Pest Monitoring and Green Management, China Agricultural University, Beijing, China
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Bi X, Li X, Yu H, An M, Li R, Xia Z, Wu Y. Development of a multiplex RT-PCR assay for simultaneous detection of Cucumber green mottle mosaic virus and Acidovorax citrulli in watermelon. PeerJ 2019; 7:e7539. [PMID: 31497401 PMCID: PMC6708580 DOI: 10.7717/peerj.7539] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2019] [Accepted: 07/23/2019] [Indexed: 11/20/2022] Open
Abstract
Watermelon (Citrullus lanatus Thunb.) is considered as a popular and nutritious fruit crop worldwide. Watermelon blood flesh disease caused by Cucumber green mottle mosaic virus (CGMMV) and bacterial fruit blotch caused by Acidovorax citrulli, are two major quarantine diseases of watermelon and result in considerable losses to global watermelon production. In this study, a multiplex reverse-transcription polymerase chain reaction (RT-PCR) method was developed for simultaneous detection of CGMMV and A. citrulli in both watermelon leaves and seeds. Two pairs of specific primers were designed based on the conserved sequences of the genomic RNA of CGMMV and the internal transcribed spacer of A. citrulli, respectively. Transcriptional elongation factor-1α from watermelon was added as an internal reference gene to prevent false negatives. No cross-reactivity was detected with other viral or bacterial pathogens infecting watermelon. Moreover, the multiplex RT-PCR showed high sensitivity and could simultaneously detect CGMMV and A. citrulli as little as 102 copies of plasmid DNA. This method was successfully applied to test field-collected watermelon leaves and stored seeds of cucurbitaceous crops. These results suggested that the developed multiplex RT-PCR technique is a rapid, efficient, and sensitive method for simultaneous detection of CGMMV and A. citrulli, providing technical support for monitoring, predicting, and preventing these two quarantine diseases. To our knowledge, this is the first report on simultaneous detection of a virus and a bacterium by multiplex RT-PCR in watermelon.
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Affiliation(s)
- Xinyue Bi
- College of Plant Protection, Shenyang Agricultural University, Shenyang, Liaoning, China
| | - Xiaodong Li
- College of Plant Protection, Shenyang Agricultural University, Shenyang, Liaoning, China
- General Station of Forest and Grassland Pest and Diseases Control, National Forestry and Grassland Administration, Shenyang, Liaoning, China
| | - Haibo Yu
- College of Plant Protection, Shenyang Agricultural University, Shenyang, Liaoning, China
| | - Mengnan An
- College of Plant Protection, Shenyang Agricultural University, Shenyang, Liaoning, China
| | - Rui Li
- College of Plant Protection, Shenyang Agricultural University, Shenyang, Liaoning, China
| | - Zihao Xia
- College of Plant Protection, Shenyang Agricultural University, Shenyang, Liaoning, China
| | - Yuanhua Wu
- College of Plant Protection, Shenyang Agricultural University, Shenyang, Liaoning, China
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23
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Yang R, Santos Garcia D, Pérez Montaño F, da Silva GM, Zhao M, Jiménez Guerrero I, Rosenberg T, Chen G, Plaschkes I, Morin S, Walcott R, Burdman S. Complete Assembly of the Genome of an Acidovorax citrulli Strain Reveals a Naturally Occurring Plasmid in This Species. Front Microbiol 2019; 10:1400. [PMID: 31281298 PMCID: PMC6595937 DOI: 10.3389/fmicb.2019.01400] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2018] [Accepted: 06/04/2019] [Indexed: 11/13/2022] Open
Abstract
Acidovorax citrulli is the causal agent of bacterial fruit blotch (BFB), a serious threat to cucurbit crop production worldwide. Based on genetic and phenotypic properties, A. citrulli strains are divided into two major groups: group I strains have been generally isolated from melon and other non-watermelon cucurbits, while group II strains are closely associated with watermelon. In a previous study, we reported the genome of the group I model strain, M6. At that time, the M6 genome was sequenced by MiSeq Illumina technology, with reads assembled into 139 contigs. Here, we report the assembly of the M6 genome following sequencing with PacBio technology. This approach not only allowed full assembly of the M6 genome, but it also revealed the occurrence of a ∼53 kb plasmid. The M6 plasmid, named pACM6, was further confirmed by plasmid extraction, Southern-blot analysis of restricted fragments and obtention of M6-derivative cured strains. pACM6 occurs at low copy numbers (average of ∼4.1 ± 1.3 chromosome equivalents) in A. citrulli M6 and contains 63 open reading frames (ORFs), most of which (55.6%) encoding hypothetical proteins. The plasmid contains several genes encoding type IV secretion components, and typical plasmid-borne genes involved in plasmid maintenance, replication and transfer. The plasmid also carries an operon encoding homologs of a Fic-VbhA toxin-antitoxin (TA) module. Transcriptome data from A. citrulli M6 revealed that, under the tested conditions, the genes encoding the components of this TA system are among the highest expressed genes in pACM6. Whether this TA module plays a role in pACM6 maintenance is still to be determined. Leaf infiltration and seed transmission assays revealed that, under tested conditions, the loss of pACM6 did not affect the virulence of A. citrulli M6. We also show that pACM6 or similar plasmids are present in several group I strains, but absent in all tested group II strains of A. citrulli.
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Affiliation(s)
- Rongzhi Yang
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Diego Santos Garcia
- Department of Entomology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Francisco Pérez Montaño
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.,Department of Microbiology, University of Seville, Seville, Spain
| | - Gustavo Mateus da Silva
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Mei Zhao
- Department of Plant Pathology, University of Georgia, Athens, GA, United States
| | - Irene Jiménez Guerrero
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Tally Rosenberg
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Gong Chen
- Department of Plant Pathology, University of Georgia, Athens, GA, United States
| | - Inbar Plaschkes
- Bioinformatics Unit, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Shai Morin
- Department of Entomology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
| | - Ron Walcott
- Department of Plant Pathology, University of Georgia, Athens, GA, United States
| | - Saul Burdman
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel
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24
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Traore SM, Eckshtain‐Levi N, Miao J, Castro Sparks A, Wang Z, Wang K, Li Q, Burdman S, Walcott R, Welbaum GE, Zhao B. Nicotiana species as surrogate host for studying the pathogenicity of Acidovorax citrulli, the causal agent of bacterial fruit blotch of cucurbits. MOLECULAR PLANT PATHOLOGY 2019; 20:800-814. [PMID: 30938096 PMCID: PMC6637898 DOI: 10.1111/mpp.12792] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Bacterial fruit blotch (BFB) caused by Acidovorax citrulli is one of the most important bacterial diseases of cucurbits worldwide. However, the mechanisms associated with A. citrulli pathogenicity and genetics of host resistance have not been extensively investigated. We idenitfied Nicotiana benthamiana and Nicotiana tabacum as surrogate hosts for studying A. citrulli pathogenicity and non-host resistance triggered by type III secreted (T3S) effectors. Two A. citrulli strains, M6 and AAC00-1, that represent the two major groups amongst A. citrulli populations, induced disease symptoms on N. benthamiana, but triggered a hypersensitive response (HR) on N. tabacum plants. Transient expression of 19 T3S effectors from A. citrulli in N. benthamiana leaves revealed that three effectors, Aave_1548, Aave_2708, and Aave_2166, trigger water-soaking-like cell death in N. benthamiana. Aave_1548 knockout mutants of M6 and AAC00-1 displayed reduced virulence on N. benthamiana and melon (Cucumis melo L.). Transient expression of Aave_1548 and Aave_2166 effectors triggered a non-host HR in N. tabacum, which was dependent on the functionality of the immune signalling component, NtSGT1. Hence, employing Nicotiana species as surrogate hosts for studying A. citrulli pathogenicity may help characterize the function of A. citrulli T3S effectors and facilitate the development of new strategies for BFB management.
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Affiliation(s)
- Sy M. Traore
- School of Plant and Environmental SciencesVirginia TechBlacksburgVAUSA
| | - Noam Eckshtain‐Levi
- Department of Plant Pathology and MicrobiologyThe Hebrew University of JerusalemRehovotIsrael
| | - Jiamin Miao
- School of Plant and Environmental SciencesVirginia TechBlacksburgVAUSA
| | | | - Zhibo Wang
- School of Plant and Environmental SciencesVirginia TechBlacksburgVAUSA
| | - Kunru Wang
- School of Plant and Environmental SciencesVirginia TechBlacksburgVAUSA
| | - Qi Li
- School of Plant and Environmental SciencesVirginia TechBlacksburgVAUSA
| | - Saul Burdman
- Department of Plant Pathology and MicrobiologyThe Hebrew University of JerusalemRehovotIsrael
| | - Ron Walcott
- Department of Plant PathologyUniversity of GeorgiaAthensGAUSA
| | | | - Bingyu Zhao
- School of Plant and Environmental SciencesVirginia TechBlacksburgVAUSA
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25
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Rosenberg T, Salam BB, Burdman S. Association Between Loss of Type IV Pilus Synthesis Ability and Phenotypic Variation in the Cucurbit Pathogenic Bacterium Acidovorax citrulli. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2018; 31:548-559. [PMID: 29298127 DOI: 10.1094/mpmi-12-17-0324-r] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Acidovorax citrulli is the causal agent of bacterial fruit blotch of cucurbits. We have shown that functional type IV pili (T4P) are required for full virulence of this bacterium. To identify A. citrulli genes required for T4P activity, we screened a library of about 10,000 transposon mutants of A. citrulli M6 for altered T4P-mediated twitching motility. This screen led to the identification of 50 mutants impaired in twitching ability due to transposon insertions into 20 different genes. Representative mutants with disruptions in these genes were further characterized. All mutants were compromised in their virulence in seed transmission and stem inoculation assays and had reduced biofilm formation ability relative to wild-type M6. When grown on nutrient agar, most mutants produced colonies with a translucent and fuzzy appearance, in contrast to the opaque and smooth appearance of wild-type colonies. The colony morphology of these mutants was identical to that of previously reported phenotypic variants of strain M6. The exceptions were M6 mutants disrupted in genes tonB, pilT, pilW, and pilX that exhibited typical wild-type colony morphology, although lacking twitching haloes surrounding the colony. Transmission electron microscopy revealed that most mutants lacked the ability to produce T4P. The exceptions were mutants with disruptions in tonB, pilT, pilW, and pilX genes that were shown to produce these appendages. These findings support the idea that colony phenotypic variation in A. citrulli is determined by the lack of ability to synthesize T4P but not by lack of T4P functionality.
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Affiliation(s)
- Tally Rosenberg
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel
| | - Bolaji Babajide Salam
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel
| | - Saul Burdman
- Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel
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26
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Zhang X, Zhao M, Yan J, Yang L, Yang Y, Guan W, Walcott R, Zhao T. Involvement of hrpX and hrpG in the Virulence of Acidovorax citrulli Strain Aac5, Causal Agent of Bacterial Fruit Blotch in Cucurbits. Front Microbiol 2018; 9:507. [PMID: 29636729 PMCID: PMC5880930 DOI: 10.3389/fmicb.2018.00507] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2017] [Accepted: 03/06/2018] [Indexed: 01/01/2023] Open
Abstract
Acidovorax citrulli causes bacterial fruit blotch, a disease that poses a global threat to watermelon and melon production. Despite its economic importance, relatively little is known about the molecular mechanisms of pathogenicity and virulence of A. citrulli. Like other plant-pathogenic bacteria, A. citrulli relies on a type III secretion system (T3SS) for pathogenicity. On the basis of sequence and operon arrangement analyses, A. citrulli was found to have a class II hrp gene cluster similar to those of Xanthomonas and Ralstonia spp. In the class II hrp cluster, hrpG and hrpX play key roles in the regulation of T3SS effectors. However, little is known about the regulation of the T3SS in A. citrulli. This study aimed to investigate the roles of hrpG and hrpX in A. citrulli pathogenicity. We found that hrpG or hrpX deletion mutants of the A. citrulli group II strain Aac5 had reduced pathogenicity on watermelon seedlings, failed to induce a hypersensitive response in tobacco, and elicited higher levels of reactive oxygen species in Nicotiana benthamiana than the wild-type strain. Additionally, we demonstrated that HrpG activates HrpX in A. citrulli. Moreover, transcription and translation of the type 3-secreted effector (T3E) gene Aac5_2166 were suppressed in hrpG and hrpX mutants. Notably, hrpG and hrpX appeared to modulate biofilm formation. These results suggest that hrpG and hrpX are essential for pathogenicity, regulation of T3Es, and biofilm formation in A. citrulli.
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Affiliation(s)
- Xiaoxiao Zhang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Mei Zhao
- Department of Plant Pathology, University of Georgia, Athens, GA, United States
| | - Jianpei Yan
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China.,Faculty of Agronomy, Jilin Agricultural University, Changchun, China
| | - Linlin Yang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China.,Plant Protection College, Shenyang Agricultural University, Shenyang, China
| | - Yuwen Yang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Wei Guan
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Ron Walcott
- Department of Plant Pathology, University of Georgia, Athens, GA, United States
| | - Tingchang Zhao
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
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27
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Fan H, Zhang Z, Li Y, Zhang X, Duan Y, Wang Q. Biocontrol of Bacterial Fruit Blotch by Bacillus subtilis 9407 via Surfactin-Mediated Antibacterial Activity and Colonization. Front Microbiol 2017; 8:1973. [PMID: 29075242 PMCID: PMC5641556 DOI: 10.3389/fmicb.2017.01973] [Citation(s) in RCA: 56] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2017] [Accepted: 09/25/2017] [Indexed: 01/08/2023] Open
Abstract
In this study, Bacillus subtilis 9407 showed a strong antibacterial activity against Acidovorax citrulli in vitro and 61.7% biocontrol efficacy on melon seedlings 4 days post inoculation under greenhouse conditions. To understand the biocontrol mechanism of B. subtilis 9407, identify the primary antibacterial compound and determine its role in controlling bacterial fruit blotch (BFB), a srfAB deletion mutant (ΔsrfAB) was constructed. The ΔsrfAB which was deficient in production of surfactin, not only showed almost no ability to inhibit growth of A. citrulli but also decreased biofilm formation and reduced swarming motility. Colonization assay demonstrated that B. subtilis 9407 could conlonize on melon roots and leaves in a large population, while ΔsrfAB showed a four- to ten-fold reduction in colonization of melon roots and leaves. Furthermore, a biocontrol assay showed that ΔsrfAB lost the biocontrol efficacy. In summary, our results indicated that surfactin, which consists of C13- to C16-surfactin A was the primary antibacterial compound of B. subtilis 9407, and it played a major role in biofilm formation, swarming motility, colonization and suppressing BFB. We propose that the biocontrol activity of B. subtilis 9407 is the results of the coordinated action of surfactin-mediated antibacterial activity and colonization. This study reveals for the first time that the use of a B. subtilis strain as a potential biological control agent could efficiently control BFB by producing surfactin.
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Affiliation(s)
| | | | | | | | | | - Qi Wang
- Department of Plant Pathology, College of Plant Protection, China Agricultural University, Beijing, China
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28
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Zivanovic M, Walcott RR. Further Characterization of Genetically Distinct Groups of Acidovorax citrulli Strains. PHYTOPATHOLOGY 2017; 107:29-35. [PMID: 27618192 DOI: 10.1094/phyto-06-16-0245-r] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Bacterial fruit blotch of cucurbits (BFB) is caused by the gram-negative bacterium Acidovorax citrulli, whose populations can be distinguished into two genetically distinct groups, I and II. Based on visual assessment of BFB severity on cucurbit seedlings and fruit after inoculation under greenhouse conditions, group I A. citrulli strains have been reported to be moderately to highly virulent on several cucurbit hosts, whereas group II strains have exhibited high virulence on watermelon but low virulence on other cucurbits. Additionally, group I strains are recovered from a range of cucurbit hosts, while group II strains are predominantly found on watermelon. The goal of this research was to develop tools to characterize and rapidly distinguish group I and II A. citrulli strains. We first sought to determine whether quantification of A. citrulli colonization of cucurbit seedling tissue reflects the differences between group I and II strains established by visual assessment of BFB symptom severity. Spray inoculation of melon seedlings with cell suspensions containing approximately 1 × 104 CFU/ml resulted in significantly higher (P = 0.01) population growth of M6 (group I; mean area under population growth curve [AUPGC] = 43.73) than that of AAC00-1 (group II; mean AUPGC = 39.33) by 10 days after inoculation. We also investigated the natural spread of bacterial cells and the resulting BFB incidence on watermelon and melon seedlings exposed to three group I and three group II A. citrulli strains under mist chamber conditions. After 5 days of exposure, the mean BFB incidence on melon seedlings exposed to representative group II A. citrulli strains was significantly lower (25 and 3.98% in experiments 1 and 2, respectively) than on melon seedlings exposed to representative group I strains (94.44 and 76.11% in experiments 1 and 2, respectively), and on watermelon seedlings exposed to representative group I and II strains (70 to 93.33%). Finally, we developed a polymerase chain reaction assay based on the putative type III secretion effector gene, Aave_2166, to rapidly distinguish group I and II A. citrulli strains. This assay will be important for future epidemiological studies on BFB.
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Affiliation(s)
- M Zivanovic
- Department of Plant Pathology, The University of Georgia, Athens 30602
| | - R R Walcott
- Department of Plant Pathology, The University of Georgia, Athens 30602
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29
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Luo J, Qiu W, Chen L, Anjum SI, Yu M, Shan C, Ilyas M, Li B, Wang Y, Sun G. Identification of Pathogenicity-Related Genes in Biofilm-Defective Acidovorax citrulli by Transposon Tn5 Mutagenesis. Int J Mol Sci 2015; 16:28050-62. [PMID: 26602922 PMCID: PMC4691024 DOI: 10.3390/ijms161226076] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2015] [Revised: 11/10/2015] [Accepted: 11/16/2015] [Indexed: 11/16/2022] Open
Abstract
Biofilm formation is important for virulence of a large number of plant pathogenic bacteria. Indeed, some virulence genes have been found to be involved in the formation of biofilm in bacterial fruit blotch pathogen Acidovorax citrulli. However, some virulent strains of A. citrulli were unable to format biofilm, indicating the complexity between biofilm formation and virulence. In this study, virulence-related genes were identified in the biofilm-defective strain A1 of A. citrulli by using Tn5 insertion, pathogenicity test, and high-efficiency thermal asymmetric interlaced PCR (hiTAIL-PCR). Results from this study indicated that 22 out of the obtained 301 mutants significantly decreased the virulence of strain A1 compared to the wild-type. Furthermore, sequence analysis indicated that the obtained 22 mutants were due to the insertion of Tn5 into eight genes, including Aave 4244 (cation diffusion facilitator family transporter), Aave 4286 (hypothetical protein), Aave 4189 (alpha/beta hydrolase fold), Aave 1911 (IMP dehydrogenase/GMP reductase domain), Aave 4383 (bacterial export proteins, family 1), Aave 4256 (Hsp70 protein), Aave 0003 (histidine kinase, DNA gyrase B, and HSP90-like ATPase), and Aave 2428 (pyridoxal-phosphate dependent enzyme). Furthermore, the growth of mutant Aave 2428 was unaffected and even increased by the change in incubation temperature, NaCl concentration and the pH of the LB broth, indicating that this gene may be directly involved in the bacterial virulence. Overall, the determination of the eight pathogenicity-related genes in strain A1 will be helpful to elucidate the pathogenesis of biofilm-defective A. citrulli.
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Affiliation(s)
- Jinyan Luo
- Department of Plant Quarantine, Shanghai Extension and Service Center of Agriculture Technology, Shanghai 201103, China.
| | - Wen Qiu
- State Key Laboratory of Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou 310058, China.
| | - Lei Chen
- Department of Plant Quarantine, Shanghai Extension and Service Center of Agriculture Technology, Shanghai 201103, China.
| | - Syed Ishtiaq Anjum
- State Key Laboratory of Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou 310058, China.
- Department of Zoology, Kohat University of Science and Technology, Kohat 26000, Pakistan.
| | - Menghao Yu
- State Key Laboratory of Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou 310058, China.
| | - Changlin Shan
- State Key Laboratory of Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou 310058, China.
- Department of Plant Quarantine, Zhoushan Entry-Exit Inspections and Quarantine Bureau, Hangzhou 310012, China.
| | - Mehmoona Ilyas
- Department of Biotechnology, University of Sargodha, Sargodha 40100, Pakistan.
| | - Bin Li
- State Key Laboratory of Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou 310058, China.
| | - Yanli Wang
- State Key Laboratory Breeding Base for Zhejiang Sustainable Plant Pest and Disease Control, Key Laboratory of Detection for Pesticide Residues, Ministry of Agriculture, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China.
| | - Guochang Sun
- State Key Laboratory Breeding Base for Zhejiang Sustainable Plant Pest and Disease Control, Key Laboratory of Detection for Pesticide Residues, Ministry of Agriculture, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China.
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30
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Tian Y, Zhao Y, Wu X, Liu F, Hu B, Walcott RR. The type VI protein secretion system contributes to biofilm formation and seed-to-seedling transmission of Acidovorax citrulli on melon. MOLECULAR PLANT PATHOLOGY 2015; 16:38-47. [PMID: 24863458 PMCID: PMC6638315 DOI: 10.1111/mpp.12159] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
The type VI protein secretion system (T6SS) is essential for the virulence of several Gram-negative bacteria. In this study, we identified a T6SS gene cluster in Acidovorax citrulli, a plant-pathogenic bacterium that causes bacterial fruit blotch (BFB) of cucurbits. One T6SS cluster, of approximately 25 kb in length and comprising 17 genes, was found in the A. citrulli AAC00-1 genome. Seventeen A. citrulli mutants were generated, each with a deletion of a single T6SS core gene. There were significant differences in BFB seed-to-seedling transmission between wild-type A. citrulli strain, xjl12, and ΔvasD, ΔimpK, ΔimpJ and ΔimpF mutants (71.71%, 9.83%, 8.41%, 7.15% and 5.99% BFB disease index, respectively). In addition, we observed that these four mutants were reduced in melon seed colonization and biofilm formation; however, they were not affected in virulence when infiltrated into melon seedling tissues. There were no significant differences in BFB seed-to-seedling transmission, melon tissue colonization and biofilm formation between xjl12 and the other 13 T6SS mutants. Overall, our results indicate that T6SS plays a role in seed-to-seedling transmission of BFB on melon.
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Affiliation(s)
- Yanli Tian
- College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing Agricultural University, Nanjing, 210095, China
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Eckshtain-Levi N, Munitz T, Živanović M, Traore SM, Spröer C, Zhao B, Welbaum G, Walcott R, Sikorski J, Burdman S. Comparative Analysis of Type III Secreted Effector Genes Reflects Divergence of Acidovorax citrulli Strains into Three Distinct Lineages. PHYTOPATHOLOGY 2014; 104:1152-1162. [PMID: 24848275 DOI: 10.1094/phyto-12-13-0350-r] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Acidovorax citrulli causes bacterial fruit blotch of cucurbits, a serious economic threat to watermelon (Citrullus lanatus) and melon (Cucumis melo) production worldwide. Based on genetic and biochemical traits, A. citrulli strains have been divided into two distinct groups: group I strains have been mainly isolated from various non-watermelon hosts, while group II strains have been generally isolated from and are highly virulent on watermelon. The pathogen depends on a functional type III secretion system for pathogenicity. Annotation of the genome of the group II strain AAC00-1 revealed 11 genes encoding putative type III secreted (T3S) effectors. Due to the crucial role of type III secretion for A. citrulli pathogenicity, we hypothesized that group I and II strains differ in their T3S effector repertoire. Comparative analysis of the 11 effector genes from a collection of 22 A. citrulli strains confirmed this hypothesis. Moreover, this analysis led to the identification of a third A. citrulli group, which was supported by DNA:DNA hybridization, DNA fingerprinting, multilocus sequence analysis of conserved genes, and virulence assays. The effector genes assessed in this study are homologous to effectors from other plant-pathogenic bacteria, mainly belonging to Xanthomonas spp. and Ralstonia solanacearum. Analyses of the effective number of codons and gas chromatography content of effector genes relative to a representative set of housekeeping genes support the idea that these effector genes were acquired by lateral gene transfer. Further investigation is required to identify new T3S effectors of A. citrulli and to determine their contribution to virulence and host preferential association.
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Dutta B, Gitaitis R, Smith S, Langston D. Interactions of seedborne bacterial pathogens with host and non-host plants in relation to seed infestation and seedling transmission. PLoS One 2014; 9:e99215. [PMID: 24936863 PMCID: PMC4061015 DOI: 10.1371/journal.pone.0099215] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2014] [Accepted: 05/12/2014] [Indexed: 11/18/2022] Open
Abstract
The ability of seed-borne bacterial pathogens (Acidovorax citrulli, Clavibacter michiganensis subsp. michiganensis, Pseudomonas syringae pv. tomato, Xanthomonas euvesicatoria, and Pseudomonas syringae pv. glycinea) to infest seeds of host and non-host plants (watermelon, tomato, pepper, and soybean) and subsequent pathogen transmission to seedlings was investigated. A non-pathogenic, pigmented strain of Serratia marcescens was also included to assess a null-interacting situation with the same plant species. Flowers of host and non-host plants were inoculated with 1 × 10(6) colony forming units (CFUs)/flower for each bacterial species and allowed to develop into fruits or umbels (in case of onion). Seeds harvested from each host/non-host bacterial species combination were assayed for respective bacteria by plating on semi-selective media. Additionally, seedlots for each host/non-host bacterial species combination were also assayed for pathogen transmission by seedling grow-out (SGO) assays under greenhouse conditions. The mean percentage of seedlots infested with compatible and incompatible pathogens was 31.7 and 30.9% (by plating), respectively and they were not significantly different (P = 0.67). The percentage of seedlots infested with null-interacting bacterial species was 16.8% (by plating) and it was significantly lower than the infested lots generated with compatible and incompatible bacterial pathogens (P = 0.03). None of the seedlots with incompatible/null-interacting bacteria developed symptoms on seedlings; however, when seedlings were assayed for epiphytic bacterial presence, 19.5 and 9.4% of the lots were positive, respectively. These results indicate that the seeds of non-host plants can become infested with incompatible and null-interacting bacterial species through flower colonization and they can be transmitted via epiphytic colonization of seedlings. In addition, it was also observed that flowers and seeds of non-host plants can be colonized by compatible/incompatible/null-interacting bacteria to higher populations; however, the level of colonization differed significantly depending on the type of bacterial species used.
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Affiliation(s)
- Bhabesh Dutta
- Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton, Georgia, United States of America
| | - Ronald Gitaitis
- Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton, Georgia, United States of America
| | - Samuel Smith
- Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton, Georgia, United States of America
| | - David Langston
- Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton, Georgia, United States of America
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Li B, Shi Y, Shan C, Zhou Q, Ibrahim M, Wang Y, Wu G, Li H, Xie G, Sun G. Effect of chitosan solution on the inhibition of Acidovorax citrulli causing bacterial fruit blotch of watermelon. JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE 2013; 93:1010-1015. [PMID: 23400827 DOI: 10.1002/jsfa.5812] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2012] [Revised: 05/21/2012] [Accepted: 06/19/2012] [Indexed: 06/01/2023]
Abstract
BACKGROUND The production of watermelon in China has been seriously hampered by fruit blotch disease and limited control measures are now applied. Chitosan has been employed to control a variety of plant diseases and is considered to be the most promising biochemical to control this disease. RESULTS The in vitro antibacterial effect of chitosan and its ability in protection of watermelon seedlings from bacterial fruit blotch were evaluated. Results showed that three types of chitosan, in particular, chitosan A at 0.40 mg mL⁻¹ significantly inhibited the growth of Acidovorax citrulli. The antibacterial activity of chitosan A was affected by chitosan concentration and incubation time. The direct antibacterial activity of chitosan may be attributed to membrane lysis evidenced by transmission electron microscopic observation. The disease index of watermelon seedlings planted in soil and the death rate of seedlings planted in perlite were significantly reduced by chitosan A at 0.40 mg mL⁻¹ compared to the pathogen control. Fresh and dry weight of watermelon seedlings planted in soil was increased by chitosan seed treatment, but not by chitosan leaf spraying. CONCLUSION The results indicated that chitosan solution may have a potential in controlling bacterial fruit blotch of watermelon.
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Affiliation(s)
- Bin Li
- State Key Laboratory of Rice Biology, Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Ministry of Agriculture, Institute of Biotechnology, Zhejiang University, Hangzhou 310029, China
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Burdman S, Walcott R. Acidovorax citrulli: generating basic and applied knowledge to tackle a global threat to the cucurbit industry. MOLECULAR PLANT PATHOLOGY 2012; 13:805-15. [PMID: 22738439 PMCID: PMC6638624 DOI: 10.1111/j.1364-3703.2012.00810.x] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
UNLABELLED Acidovorax citrulli is the causal agent of bacterial fruit blotch (BFB) of cucurbit plants. In recent years, the disease has spread to many parts of the world, mainly via the inadvertent distribution of contaminated commercial seeds. Because of the costly lawsuits filed by growers against seed companies and the lack of efficient management methods, BFB represents a serious threat to the cucurbit industry, and primarily to watermelons and melons. Despite the economic importance of the disease, little is known about the basic aspects of A. citrulli pathogenesis. Nevertheless, the release of the genome of one A. citrulli strain, as well as the optimization of molecular manipulation and inoculation methods, has prompted basic studies and allowed advances towards an understanding of A. citrulli pathogenicity. In this article, we summarize the current knowledge about this important pathogen, with emphasis on its epidemiology and the factors involved in its pathogenicity and virulence. TAXONOMY Bacteria; Betaproteobacteria; order Burkholderiales; family C omamonadaceae; genus Acidovorax; species citrulli. MICROBIOLOGICAL PROPERTIES Gram-negative, strictly aerobic, rod-shaped; average dimensions of 0.5 μm × 1.7 μm; motile by means of an ~5.0-μm-long polar flagellum; colonies on King's medium B are round, smooth, transparent and nonpigmented; optimal temperatures for growth around 27-30 °C; induces a hypersensitive response on nonhost tobacco and tomato leaves. HOST RANGE Acidovorax citrulli strains are pathogenic to various species of the Cucurbitaceae family, including watermelon, melon, squash, pumpkin and cucumber. Significant economic losses have been reported in watermelon and melon. DISEASE SYMPTOMS Watermelon and melon seedlings and fruits are highly susceptible to A. citrulli. Typical seedling symptoms include water-soaked lesions on cotyledons that are often adjacent to the veins and later become necrotic, lesions on the hypocotyl, and seedling collapse and death. On watermelon fruits, symptoms begin as small, irregular, water-soaked lesions which later extend through the rind, turn brown and crack. On melon fruits, symptoms are characterized by small, often sunken rind lesions and internal fruit decay. Symptoms on the leaves of mature plants are difficult to diagnose because they are often inconspicuous or similar to those caused by other biotic or abiotic stresses. When they occur, leaf lesions can spread along the midrib and main veins. Lesions appear dark-brown to black on watermelon and light to reddish-brown on melon. USEFUL WEBSITES Bacterial fruit blotch of cucurbits at APSnet, http://www.apsnet.org/edcenter/intropp/lessons/prokaryotes/Pages/BacterialBlotch.aspx; bacterial fruit blotch guide from ASTA, http://www.amseed.com/pdfs/DiseaseGuide-BFB-English.pdf; Acidovorax citrulli AAC00-1 genome at JGI, http://genome.jgi-psf.org/aciav/aciav.info.html.
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Affiliation(s)
- Saul Burdman
- Department of Plant Pathology and Microbiology and the Minerva Otto Warburg Center for Agricultural Biotechnology, The Hebrew University of Jerusalem, Rehovot 76100, Israel.
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