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Matte LM, Genal AV, Landolt EF, Danka ES. T6SS in plant pathogens: unique mechanisms in complex hosts. Infect Immun 2024; 92:e0050023. [PMID: 39166846 PMCID: PMC11385963 DOI: 10.1128/iai.00500-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/23/2024] Open
Abstract
Type VI secretion systems (T6SSs) are complex molecular machines that allow bacteria to deliver toxic effector proteins to neighboring bacterial and eukaryotic cells. Although initial work focused on the T6SS as a virulence mechanism of human pathogens, the field shifted to examine the use of T6SSs for interbacterial competition in various environments, including in the plant rhizosphere. Genes encoding the T6SS are estimated to be found in a quarter of all Gram-negative bacteria and are especially highly represented in Proteobacteria, a group which includes the most important bacterial phytopathogens. Many of these pathogens encode multiple distinct T6SS gene clusters which can include the core components of the apparatus as well as effector proteins. The T6SS is deployed by pathogens at multiple points as they colonize their hosts and establish an infection. In this review, we describe what is known about the use of T6SS by phytopathogens against plant hosts and non-plant organisms, keeping in mind that the structure of plants requires unique mechanisms of attack that are distinct from the mechanisms used for interbacterial interactions and against animal hosts. While the interactions of specific effectors (such as phospholipases, endonucleases, peptidases, and amidases) with targets have been well described in the context of interbacterial competition and in some eukaryotic interactions, this review highlights the need for future studies to assess the activity of phytobacterial T6SS effectors against plant cells.
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Affiliation(s)
- Lexie M Matte
- Biology Discipline, Division of Natural and Social Sciences, St. Norbert College, De Pere, Wisconsin, USA
| | - Abigail V Genal
- Biology Discipline, Division of Natural and Social Sciences, St. Norbert College, De Pere, Wisconsin, USA
| | - Emily F Landolt
- Biology Discipline, Division of Natural and Social Sciences, St. Norbert College, De Pere, Wisconsin, USA
| | - Elizabeth S Danka
- Biology Discipline, Division of Natural and Social Sciences, St. Norbert College, De Pere, Wisconsin, USA
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Ramamoorthy S, Pena M, Ghosh P, Liao YY, Paret M, Jones JB, Potnis N. Transcriptome profiling of type VI secretion system core gene tssM mutant of Xanthomonas perforans highlights regulators controlling diverse functions ranging from virulence to metabolism. Microbiol Spectr 2024; 12:e0285223. [PMID: 38018859 PMCID: PMC10782981 DOI: 10.1128/spectrum.02852-23] [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: 07/14/2023] [Accepted: 10/20/2023] [Indexed: 11/30/2023] Open
Abstract
IMPORTANCE T6SS has received attention due to its significance in mediating interorganismal competition through contact-dependent release of effector molecules into prokaryotic and eukaryotic cells. Reverse-genetic studies have indicated the role of T6SS in virulence in a variety of plant pathogenic bacteria, including the one studied here, Xanthomonas. However, it is not clear whether such effect on virulence is merely due to a shift in the microbiome-mediated protection or if T6SS is involved in a complex virulence regulatory network. In this study, we conducted in vitro transcriptome profiling in minimal medium to decipher the signaling pathways regulated by tssM-i3* in X. perforans AL65. We show that TssM-i3* regulates the expression of a suite of genes associated with virulence and metabolism either directly or indirectly by altering the transcription of several regulators. These findings further expand our knowledge on the intricate molecular circuits regulated by T6SS in phytopathogenic bacteria.
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Affiliation(s)
- Sivakumar Ramamoorthy
- Department of Entomology and Plant Pathology, Auburn University, Auburn, Alabama, USA
| | - Michelle Pena
- Department of Entomology and Plant Pathology, Auburn University, Auburn, Alabama, USA
| | - Palash Ghosh
- Department of Entomology and Plant Pathology, Auburn University, Auburn, Alabama, USA
| | - Ying-Yu Liao
- Department of Plant Pathology, University of Florida, Gainesville, Florida, USA
| | - Mathews Paret
- Department of Plant Pathology, University of Florida, Gainesville, Florida, USA
| | - Jeffrey B. Jones
- Department of Plant Pathology, University of Florida, Gainesville, Florida, USA
| | - Neha Potnis
- Department of Entomology and Plant Pathology, Auburn University, Auburn, Alabama, USA
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Bourigault Y, Dupont CA, Desjardins JB, Doan T, Bouteiller M, Le Guenno H, Chevalier S, Barbey C, Latour X, Cascales E, Merieau A. Pseudomonas fluorescens MFE01 delivers a putative type VI secretion amidase that confers biocontrol against the soft-rot pathogen Pectobacterium atrosepticum. Environ Microbiol 2023; 25:2564-2579. [PMID: 37622480 DOI: 10.1111/1462-2920.16492] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Accepted: 08/15/2023] [Indexed: 08/26/2023]
Abstract
The type VI secretion system (T6SS) is a contractile nanomachine widespread in Gram-negative bacteria. The T6SS injects effectors into target cells including eukaryotic hosts and competitor microbial cells and thus participates in pathogenesis and intermicrobial competition. Pseudomonas fluorescens MFE01 possesses a single T6SS gene cluster that confers biocontrol properties by protecting potato tubers against the phytopathogen Pectobacterium atrosepticum (Pca). Here, we demonstrate that a functional T6SS is essential to protect potato tuber by reducing the pectobacteria population. Fluorescence microscopy experiments showed that MFE01 displays an aggressive behaviour with an offensive T6SS characterized by continuous and intense T6SS firing activity. Interestingly, we observed that T6SS firing is correlated with rounding of Pectobacterium cells, suggesting delivery of a potent cell wall targeting effector. Mutagenesis coupled with functional assays then revealed that a putative T6SS secreted amidase, Tae3Pf , is mainly responsible for MFE01 toxicity towards Pca. Further studies finally demonstrated that Tae3Pf is toxic when produced in the periplasm, and that its toxicity is counteracted by the Tai3Pf inner membrane immunity protein.
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Affiliation(s)
- Yvann Bourigault
- Laboratoire de Communication Bactérienne et Stratégies Anti-infectieuses (CBSA, UR 4312), Univ Rouen Normandie, Université Caen Normandie, Normandie Univ, Rouen, France
- Structure Fédérative de Recherche Normandie Végétale, NORVEGE Fed4277, Mont-Saint-Aignan, France
| | - Charly A Dupont
- Laboratoire de Communication Bactérienne et Stratégies Anti-infectieuses (CBSA, UR 4312), Univ Rouen Normandie, Université Caen Normandie, Normandie Univ, Rouen, France
- Structure Fédérative de Recherche Normandie Végétale, NORVEGE Fed4277, Mont-Saint-Aignan, France
| | - Jonas B Desjardins
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM, UMR 7255), Institut de Microbiologie de la Méditerranée (IMM, FR3479), CNRS-Aix-Marseille Univ, Marseille, France
| | - Thierry Doan
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM, UMR 7255), Institut de Microbiologie de la Méditerranée (IMM, FR3479), CNRS-Aix-Marseille Univ, Marseille, France
| | - Mathilde Bouteiller
- Laboratoire de Communication Bactérienne et Stratégies Anti-infectieuses (CBSA, UR 4312), Univ Rouen Normandie, Université Caen Normandie, Normandie Univ, Rouen, France
- Structure Fédérative de Recherche Normandie Végétale, NORVEGE Fed4277, Mont-Saint-Aignan, France
| | - Hugo Le Guenno
- Plateforme de Microscopie, Institut de Microbiologie de la Méditerranée (IMM, FR3479), CNRS-Aix-Marseille Univ, Marseille, France
| | - Sylvie Chevalier
- Laboratoire de Communication Bactérienne et Stratégies Anti-infectieuses (CBSA, UR 4312), Univ Rouen Normandie, Université Caen Normandie, Normandie Univ, Rouen, France
| | - Corinne Barbey
- Laboratoire de Communication Bactérienne et Stratégies Anti-infectieuses (CBSA, UR 4312), Univ Rouen Normandie, Université Caen Normandie, Normandie Univ, Rouen, France
- Structure Fédérative de Recherche Normandie Végétale, NORVEGE Fed4277, Mont-Saint-Aignan, France
| | - Xavier Latour
- Laboratoire de Communication Bactérienne et Stratégies Anti-infectieuses (CBSA, UR 4312), Univ Rouen Normandie, Université Caen Normandie, Normandie Univ, Rouen, France
- Structure Fédérative de Recherche Normandie Végétale, NORVEGE Fed4277, Mont-Saint-Aignan, France
| | - Eric Cascales
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM, UMR 7255), Institut de Microbiologie de la Méditerranée (IMM, FR3479), CNRS-Aix-Marseille Univ, Marseille, France
| | - Annabelle Merieau
- Laboratoire de Communication Bactérienne et Stratégies Anti-infectieuses (CBSA, UR 4312), Univ Rouen Normandie, Université Caen Normandie, Normandie Univ, Rouen, France
- Structure Fédérative de Recherche Normandie Végétale, NORVEGE Fed4277, Mont-Saint-Aignan, France
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An Extracytoplasmic Function Sigma Factor Required for Full Virulence in Xanthomonas citri pv. citri. J Bacteriol 2022; 204:e0062421. [PMID: 35446118 DOI: 10.1128/jb.00624-21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The genus Xanthomonas includes more than 30 phytopathogenic species that infect a wide range of plants and cause severe diseases that greatly impact crop productivity. These bacteria are highly adapted to the soil and plant environment, being found in decaying material, as epiphytes, and colonizing the plant mesophyll. Signal transduction mechanisms involved in the responses of Xanthomonas to environmental changes are still poorly characterized. Xanthomonad genomes typically encode several representatives of the extracytoplasmic function σ (σECF) factors, whose physiological roles remain elusive. In this work, we functionally characterized the Xanthomonas citri pv. citri EcfL, a σECF factor homologous to members of the iron-responsive FecI-like group. We show that EcfL is not required or induced during iron starvation, despite presenting the common features of other FecI-like σECF factors. EcfL positively regulates one operon composed of three genes that encode a TonB-dependent receptor involved in cell surface signaling, an acid phosphatase, and a lectin-domain containing protein. Furthermore, we demonstrate that EcfL is required for full virulence in citrus, and its regulon is induced inside the plant mesophyll and in response to acid stress. Together, our study suggests a role for EcfL in the adaptation of X. citri to the plant environment, in this way contributing to its ability to cause citrus canker disease. IMPORTANCE The Xanthomonas genus comprises a large number of phytopathogenic species that infect a wide variety of economically important plants worldwide. Bacterial adaptation to the plant and soil environment relies on their repertoire of signal transduction pathways, including alternative sigma factors of the extracytoplasmic function family (σECF). Here, we describe a new σECF factor found in several Xanthomonas species, demonstrating its role in Xanthomonas citri virulence to citrus plants. We show that EcfL regulates a single operon containing three genes, which are also conserved in other Xanthomonas species. This study further expands our knowledge on the functions of the widespread family of σECF factors in phytopathogenic bacteria.
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Liyanapathiranage P, Wagner N, Avram O, Pupko T, Potnis N. Phylogenetic Distribution and Evolution of Type VI Secretion System in the Genus Xanthomonas. Front Microbiol 2022; 13:840308. [PMID: 35495725 PMCID: PMC9048695 DOI: 10.3389/fmicb.2022.840308] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Accepted: 02/10/2022] [Indexed: 11/13/2022] Open
Abstract
The type VI secretion system (T6SS) present in many Gram-negative bacteria is a contact-dependent apparatus that can directly deliver secreted effectors or toxins into diverse neighboring cellular targets including both prokaryotic and eukaryotic organisms. Recent reverse genetics studies with T6 core gene loci have indicated the importance of functional T6SS toward overall competitive fitness in various pathogenic Xanthomonas spp. To understand the contribution of T6SS toward ecology and evolution of Xanthomonas spp., we explored the distribution of the three distinguishable T6SS clusters, i3*, i3***, and i4, in approximately 1,740 Xanthomonas genomes, along with their conservation, genetic organization, and their evolutionary patterns in this genus. Screening genomes for core genes of each T6 cluster indicated that 40% of the sequenced strains possess two T6 clusters, with combinations of i3*** and i3* or i3*** and i4. A few strains of Xanthomonas citri, Xanthomonas phaseoli, and Xanthomonas cissicola were the exception, possessing a unique combination of i3* and i4. The findings also indicated clade-specific distribution of T6SS clusters. Phylogenetic analysis demonstrated that T6SS clusters i3* and i3*** were probably acquired by the ancestor of the genus Xanthomonas, followed by gain or loss of individual clusters upon diversification into subsequent clades. T6 i4 cluster has been acquired in recent independent events by group 2 xanthomonads followed by its spread via horizontal dissemination across distinct clades across groups 1 and 2 xanthomonads. We also noted reshuffling of the entire core T6 loci, as well as T6SS spike complex components, hcp and vgrG, among different species. Our findings indicate that gain or loss events of specific T6SS clusters across Xanthomonas phylogeny have not been random.
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Affiliation(s)
| | - Naama Wagner
- The Shmunis School of Biomedicine and Cancer Research, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Oren Avram
- The Shmunis School of Biomedicine and Cancer Research, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Tal Pupko
- The Shmunis School of Biomedicine and Cancer Research, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Neha Potnis
- Department of Entomology and Plant Pathology, Auburn University, Auburn, AL, United States
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Liyanapathiranage P, Jones JB, Potnis N. Mutation of a Single Core Gene, tssM, of Type VI Secretion System of Xanthomonas perforans Influences Virulence, Epiphytic Survival, and Transmission During Pathogenesis on Tomato. PHYTOPATHOLOGY 2022; 112:752-764. [PMID: 34543058 DOI: 10.1094/phyto-02-21-0069-r] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Xanthomonas perforans is a seedborne hemibiotrophic pathogen that successfully establishes infection in the phyllosphere of tomato. While most studies investigating mechanistic basis of pathogenesis have focused on successful apoplastic growth, factors important during asymptomatic colonization in the early stages of disease development are not well understood. In this study, we show that tssM gene of the type VI secretion system cluster i3* (T6SS-i3*) plays a significant role during initial asymptomatic epiphytic colonization at different stages during the life cycle of the pathogen. Mutation in a core gene, tssM of T6SS-i3*, imparted higher aggressiveness to the pathogen, as indicated by higher overall disease severity, higher in planta growth, and shorter latent infection period compared with the wild-type upon dip inoculation of 4- to 5-week-old tomato plants. Contribution of tssM toward aggressiveness was evident during vertical transmission from seed to seedling, with wild-type showing reduced disease severity as well as lower in planta populations on seedlings compared with the mutant. Presence of functional TssM offered higher epiphytic fitness as well as higher dissemination potential to the pathogen when tested in an experimental setup mimicking transplant house high-humidity conditions. We showed higher osmotolerance being one mechanism by which TssM offers higher epiphytic fitness. Taken together, these data reveal that functional TssM plays a larger role in offering ecological advantage to the pathogen. TssM prolongs the association of hemibiotrophic pathogen with the host, minimizing overall disease severity yet facilitating successful dissemination.
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Affiliation(s)
| | - Jeffrey B Jones
- Department of Plant Pathology, University of Florida, Gainesville, FL 32611
| | - Neha Potnis
- Department of Entomology and Plant Pathology, Auburn University, Auburn, AL 36849
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Secrete or perish: The role of secretion systems in Xanthomonas biology. Comput Struct Biotechnol J 2020; 19:279-302. [PMID: 33425257 PMCID: PMC7777525 DOI: 10.1016/j.csbj.2020.12.020] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Revised: 12/13/2020] [Accepted: 12/13/2020] [Indexed: 12/22/2022] Open
Abstract
Bacteria of the Xanthomonas genus are mainly phytopathogens of a large variety of crops of economic importance worldwide. Xanthomonas spp. rely on an arsenal of protein effectors, toxins and adhesins to adapt to the environment, compete with other microorganisms and colonize plant hosts, often causing disease. These protein effectors are mainly delivered to their targets by the action of bacterial secretion systems, dedicated multiprotein complexes that translocate proteins to the extracellular environment or directly into eukaryotic and prokaryotic cells. Type I to type VI secretion systems have been identified in Xanthomonas genomes. Recent studies have unravelled the diverse roles played by the distinct types of secretion systems in adaptation and virulence in xanthomonads, unveiling new aspects of their biology. In addition, genome sequence information from a wide range of Xanthomonas species and pathovars have become available recently, uncovering a heterogeneous distribution of the distinct families of secretion systems within the genus. In this review, we describe the architecture and mode of action of bacterial type I to type VI secretion systems and the distribution and functions associated with these important nanoweapons within the Xanthomonas genus.
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Shahbaz MU, Qian S, Yun F, Zhang J, Yu C, Tian F, Yang F, Chen H. Identification of the Regulatory Components Mediated by the Cyclic di-GMP Receptor Filp and Its Interactor PilZX3 and Functioning in Virulence of Xanthomonas oryzae pv. oryzae. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2020; 33:1196-1208. [PMID: 32720873 DOI: 10.1094/mpmi-04-20-0088-r] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The degenerate GGDEF/EAL domain protein Filp was previously shown to function as a cyclic di-GMP (c-di-GMP) signal receptor through its specific interaction with an atypical PilZ domain protein PilZX3 (formerly PXO_02715) and that this interaction is involved in regulating virulence in Xanthomonas oryzae pv. oryzae. As a step toward understanding the regulatory role of Filp/PilZX3-mediated c-di-GMP signaling in the virulence of X. oryzae pv. oryzae, differentially expressed proteins (DEPs) downstream of Filp/PilZX3 were identified by isobaric tagging for relative and absolute quantitation (iTRAQ). A total of 2,346 proteins were identified, of which 157 displayed significant differential expression in different strains. Western blot and quantitative reverse transcription-PCR analyses showed that the expression of HrrP (histidine kinase-response regulator hybrid protein), PhrP (PhoPQ-regulated protein), ProP (prophage Lp2 protein 6) were increased in the ∆filp, ∆pilZX3, and ∆filp∆pilZX3 mutant strains, while expression of CheW1 (chemotaxis protein CheW1), EdpX2 (the second EAL domain protein identified in X. oryzae pv. oryzae), HGdpX2 (the second HD-GYP domain protein identified in X. oryzae pv. oryzae) was decreased in all mutant strains compared with that in the wild type, which was consistent with the iTRAQ data. Deletion of the hrrP and proP genes resulted in significant increases in virulence, whereas deletion of the cheW1, hGdpX2, or tdrX2 genes resulted in decreased virulence. Enzyme assays indicated that EdpX2 and HGdpX2 were active phosphodiesterases (PDEs). This study provides a proteomic description of putative regulatory pathway of Filp and PilZX3 and characterized novel factors that contributed to the virulence of X. oryzae pv. oryzae regulated by c-di-GMP signaling.
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Affiliation(s)
- Muhammad Umar Shahbaz
- State Key Laboratory for Biology Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China
- Plant Pathology Section, Plant Pathology Research Institute, AARI, Faisalabad 38850, Pakistan
| | - Shanshan Qian
- State Key Laboratory for Biology Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China
| | - Fei Yun
- National Tobacco Cultivation and Physiology and Biochemistry Research Centre/Key Laboratory for Tobacco Cultivation of Tobacco Industry, Henan Agricultural University, Zhengzhou 450002, China
| | - Jie Zhang
- State Key Laboratory for Biology Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China
| | - Chao Yu
- State Key Laboratory for Biology Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China
| | - Fang Tian
- State Key Laboratory for Biology Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China
| | - Fenghuan Yang
- State Key Laboratory for Biology Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China
| | - Huamin Chen
- State Key Laboratory for Biology Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China
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