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Drehkopf S, Scheibner F, Büttner D. Functional characterization of VirB/VirD4 and Icm/Dot type IV secretion systems from the plant-pathogenic bacterium Xanthomonas euvesicatoria. Front Cell Infect Microbiol 2023; 13:1203159. [PMID: 37593760 PMCID: PMC10432156 DOI: 10.3389/fcimb.2023.1203159] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2023] [Accepted: 07/17/2023] [Indexed: 08/19/2023] Open
Abstract
Introduction Many Gram-negative plant- and animal-pathogenic bacteria employ type IV secretion (T4S) systems to transport proteins or DNA/protein complexes into eukaryotic or bacterial target cells. T4S systems have been divided into minimized and expanded T4S systems and resemble the VirB/VirD4 T4S system from the plant pathogen Agrobacterium tumefaciens and the Icm/Dot T4S system from the human pathogen Legionella pneumophila, respectively. The only known plant pathogen with both types of T4S systems is Xanthomonas euvesicatoria which is the causal agent of bacterial spot disease on pepper and tomato plants. Results and discussion In the present study, we show that virB/virD4 and icm/dot T4S genes are expressed and encode components of oligomeric complexes corresponding to known assemblies of VirB/VirD4 and Icm/Dot proteins. Both T4S systems are dispensable for the interaction of X. euvesicatoria with its host plants and do not seem to confer contact-dependent lysis of other bacteria, which was previously shown for the chromosomally encoded VirB/VirD4 T4S system from Xanthomonas axonopodis pv. citri. The corresponding chromosomal T4S gene cluster from X. euvesicatoria is incomplete, however, the second plasmid-localized vir gene cluster encodes a functional VirB/VirD4 T4S system which contributes to plasmid transfer. In agreement with this finding, we identified the predicted relaxase TraI as substrate of the T4S systems from X. euvesicatoria. TraI and additional candidate T4S substrates with homology to T4S effectors from X. axonopodis pv. citri interact with the T4S coupling protein VirD4. Interestingly, however, the predicted C-terminal VirD4-binding sites are not sufficient for T4S, suggesting the contribution of additional yet unknown mechanisms to the targeting of T4S substrates from X. euvesicatoria to both VirB/VirD4 and Icm/Dot T4S systems.
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Affiliation(s)
| | | | - Daniela Büttner
- Institute for Biology, Department of Genetics, Martin-Luther University Halle-Wittenberg, Halle (Saale), Germany
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2
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ntrC Contributes to Nitrogen Utilization, Stress Tolerance, and Virulence in Acidovorax citrulli. Microorganisms 2023; 11:microorganisms11030767. [PMID: 36985340 PMCID: PMC10052978 DOI: 10.3390/microorganisms11030767] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2023] [Revised: 03/13/2023] [Accepted: 03/16/2023] [Indexed: 03/19/2023] Open
Abstract
Bacterial fruit blotch (BFB), caused by Acidovorax citrulli, severely damages watermelon, melon, and other cucurbit crops worldwide. Nitrogen, one of the most important limiting elements in the environment, is necessary for the growth and reproduction of bacteria. As a nitrogen-regulating gene, ntrC plays an important role in maintaining bacterial nitrogen utilization and biological nitrogen fixation. However, the role of ntrC has not been determined for A. citrulli. In this study, we constructed a ntrC deletion mutant and a corresponding complementary strain in the background of the A. citrulli wild-type strain, Aac5. Through phenotype assays and qRT-PCR analysis, we investigated the role of ntrC in A. citrulli in nitrogen utilization, stress tolerance, and virulence against watermelon seedlings. Our results showed that the A. citrulli Aac5 ntrC deletion mutant lost the ability to utilize nitrate. The ntrC mutant strain also exhibited significantly decreased virulence, in vitro growth, in vivo colonization ability, swimming motility, and twitching motility. In contrast, it displayed significantly enhanced biofilm formation and tolerance to stress induced by oxygen, high salt, and copper ions. The qRT-PCR results showed that the nitrate utilization gene nasS; the Type III secretion system-related genes hrpE, hrpX, and hrcJ; and the pili-related gene pilA were significantly downregulated in the ntrC deletion mutant. The nitrate utilization gene nasT, and the flagellum-related genes flhD, flhC, fliA, and fliC were significantly upregulated in the ntrC deletion mutant. The expression levels of ntrC gene in the MMX-q and XVM2 media were significantly higher than in the KB medium. These results suggest that the ntrC gene plays a pivotal role in the nitrogen utilization, stress tolerance, and virulence of A. citrulli.
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Drehkopf S, Otten C, Büttner D. Recognition of a translocation motif in the regulator HpaA from Xanthomonas euvesicatoria is controlled by the type III secretion chaperone HpaB. FRONTIERS IN PLANT SCIENCE 2022; 13:955776. [PMID: 35968103 PMCID: PMC9366055 DOI: 10.3389/fpls.2022.955776] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/29/2022] [Accepted: 07/08/2022] [Indexed: 06/15/2023]
Abstract
The Gram-negative plant-pathogenic bacterium Xanthomonas euvesicatoria is the causal agent of bacterial spot disease in pepper and tomato plants. Pathogenicity of X. euvesicatoria depends on a type III secretion (T3S) system which translocates effector proteins into plant cells and is associated with an extracellular pilus and a translocon in the plant plasma membrane. Effector protein translocation is activated by the cytoplasmic T3S chaperone HpaB which presumably targets effectors to the T3S system. We previously reported that HpaB is controlled by the translocated regulator HpaA which binds to and inactivates HpaB during the assembly of the T3S system. In the present study, we show that translocation of HpaA depends on the T3S substrate specificity switch protein HpaC and likely occurs after pilus and translocon assembly. Translocation of HpaA requires the presence of a translocation motif (TrM) in the N-terminal region. The TrM consists of an arginine-and proline-rich amino acid sequence and is also essential for the in vivo function of HpaA. Mutation of the TrM allowed the translocation of HpaA in hpaB mutant strains but not in the wild-type strain, suggesting that the recognition of the TrM depends on HpaB. Strikingly, the contribution of HpaB to the TrM-dependent translocation of HpaA was independent of the presence of the C-terminal HpaB-binding site in HpaA. We propose that HpaB generates a recognition site for the TrM at the T3S system and thus restricts the access to the secretion channel to effector proteins. Possible docking sites for HpaA at the T3S system were identified by in vivo and in vitro interaction studies and include the ATPase HrcN and components of the predicted cytoplasmic sorting platform of the T3S system. Notably, the TrM interfered with the efficient interaction of HpaA with several T3S system components, suggesting that it prevents premature binding of HpaA. Taken together, our data highlight a yet unknown contribution of the TrM and HpaB to substrate recognition and suggest that the TrM increases the binding specificity between HpaA and T3S system components.
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Otten C, Seifert T, Hausner J, Büttner D. The Contribution of the Predicted Sorting Platform Component HrcQ to Type III Secretion in Xanthomonas campestris pv. vesicatoria Depends on an Internal Translation Start Site. Front Microbiol 2021; 12:752733. [PMID: 34721356 PMCID: PMC8553256 DOI: 10.3389/fmicb.2021.752733] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Accepted: 09/22/2021] [Indexed: 11/13/2022] Open
Abstract
Pathogenicity of the Gram-negative bacterium Xanthomonas campestris pv. vesicatoria depends on a type III secretion (T3S) system which translocates effector proteins into plant cells. T3S systems are conserved in plant- and animal-pathogenic bacteria and consist of at least nine structural core components, which are designated Sct (secretion and cellular translocation) in animal-pathogenic bacteria. Sct proteins are involved in the assembly of the membrane-spanning secretion apparatus which is associated with an extracellular needle structure and a cytoplasmic sorting platform. Components of the sorting platform include the ATPase SctN, its regulator SctL, and pod-like structures at the periphery of the sorting platform consisting of SctQ proteins. Members of the SctQ family form a complex with the C-terminal protein domain, SctQC, which is translated as separate protein and likely acts either as a structural component of the sorting platform or as a chaperone for SctQ. The sorting platform has been intensively studied in animal-pathogenic bacteria but has not yet been visualized in plant pathogens. We previously showed that the SctQ homolog HrcQ from X. campestris pv. vesicatoria assembles into complexes which associate with the T3S system and interact with components of the ATPase complex. Here, we report the presence of an internal alternative translation start site in hrcQ leading to the separate synthesis of the C-terminal protein region (HrcQC). The analysis of genomic hrcQ mutants showed that HrcQC is essential for pathogenicity and T3S. Increased expression levels of hrcQ or the T3S genes, however, compensated the lack of HrcQC. Interaction studies and protein analyses suggest that HrcQC forms a complex with HrcQ and promotes HrcQ stability. Furthermore, HrcQC colocalizes with HrcQ as was shown by fluorescence microscopy, suggesting that it is part of the predicted cytoplasmic sorting platform. In agreement with this finding, HrcQC interacts with the inner membrane ring protein HrcD and the SctK-like linker protein HrpB4 which contributes to the docking of the HrcQ complex to the membrane-spanning T3S apparatus. Taken together, our data suggest that HrcQC acts as a chaperone for HrcQ and as a structural component of the predicted sorting platform.
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Affiliation(s)
- Christian Otten
- Department of Genetics, Institute for Biology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Tanja Seifert
- Department of Genetics, Institute for Biology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Jens Hausner
- Department of Genetics, Institute for Biology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Daniela Büttner
- Department of Genetics, Institute for Biology, Martin Luther University Halle-Wittenberg, Halle, Germany
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5
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Otten C, Büttner D. HrpB4 from Xanthomonas campestris pv. vesicatoria acts similarly to SctK proteins and promotes the docking of the predicted sorting platform to the type III secretion system. Cell Microbiol 2021; 23:e13327. [PMID: 33733571 DOI: 10.1111/cmi.13327] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2020] [Revised: 02/28/2021] [Accepted: 03/15/2021] [Indexed: 11/28/2022]
Abstract
The Gram-negative bacterium Xanthomonas campestris pv. vesicatoria is the causal agent of bacterial spot disease on pepper and tomato plants. Pathogenicity of X. campestris pv. vesicatoria depends on a type III secretion (T3S) system which translocates bacterial effector proteins into plant cells. At least nine membrane-associated and cytoplasmic components of the secretion apparatus are homologous to corresponding Sct (secretion and cellular translocation) proteins from animal pathogens, suggesting a similar structural organisation of T3S systems in different bacterial species. T3S in X. campestris pv. vesicatoria also depends on non-conserved proteins with yet unknown function including the essential pathogenicity factor HrpB4. Here, we show that HrpB4 localises to the cytoplasm and the bacterial membranes and interacts with the cytoplasmic domain of the inner membrane (IM) ring component HrcD and the cytoplasmic HrcQ protein. The analysis of HrpB4 deletion derivatives revealed that deletion of the N- or C-terminal protein region affects the interaction of HrpB4 with HrcQ and HrcD as well as its contribution to pathogenicity. HrcQ is a component of the predicted sorting platform, which was identified in animal pathogens as a dynamic heterooligomeric protein complex and associates with the IM ring via SctK proteins. HrcQ complex formation was previously shown by fluorescent microscopy analysis and depends on the presence of the T3S system. In the present study, we provide experimental evidence that the absence of HrpB4 severely affects the docking of HrcQ complexes to the T3S system but does not significantly interfere with HrcQ complex formation in the bacterial cytoplasm. Taken together, our data suggest that HrpB4 links the predicted cytoplasmic sorting platform to the IM rings of the T3S system.
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Affiliation(s)
- Christian Otten
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Daniela Büttner
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
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6
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Gan YL, Yang LY, Yang LC, Li WL, Liang XL, Jiang W, Jiang GF, Hang XH, Yang M, Tang JL, Jiang BL. The C-terminal domain of the type III secretion chaperone HpaB contributes to dissociation of chaperone-effector complex in Xanthomonas campestris pv. campestris. PLoS One 2021; 16:e0246033. [PMID: 33507993 PMCID: PMC7842900 DOI: 10.1371/journal.pone.0246033] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Accepted: 01/12/2021] [Indexed: 12/01/2022] Open
Abstract
Many animal and plant pathogenic bacteria employ a type three secretion system (T3SS) to deliver type three effector proteins (T3Es) into host cells. Efficient secretion of many T3Es in the plant pathogen Xanthomonas campestris pv. campestris (Xcc) relies on the global chaperone HpaB. However, how the domain of HpaB itself affects effector translocation/secretion is poorly understood. Here, we used genetic and biochemical approaches to identify a novel domain at the C-terminal end of HpaB (amino acid residues 137-160) that contributes to virulence and hypersensitive response (HR). Both in vitro secretion assay and in planta translocation assay showed that the secretion and translocation of T3E proteins depend on the C-terminal region of HpaB. Deletion of the C-terminal region of HpaB did not affect binding to T3Es, self-association or interaction with T3SS components. However, the deletion of C-terminal region sharply reduced the mounts of free T3Es liberated from the complex of HpaB with the T3Es, a reaction catalyzed in an ATP-dependent manner by the T3SS-associated ATPase HrcN. Our findings demonstrate the C-terminal domain of HpaB contributes to disassembly of chaperone-effector complex and reveal a potential molecular mechanism underpinning the involvement of HpaB in secretion of T3Es in Xcc.
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Affiliation(s)
- Yong-Liang Gan
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning, China
| | - Li-Yan Yang
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning, China
| | - Li-Chao Yang
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning, China
| | - Wan-Lian Li
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning, China
| | - Xue-Lian Liang
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning, China
| | - Wei Jiang
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning, China
| | | | - Xiao-Hong Hang
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning, China
| | - Mei Yang
- School of Chemistry and Chemical Engineering, Guangxi University, Nanning, China
| | - Ji-Liang Tang
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning, China
| | - Bo-Le Jiang
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning, China
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Milne-Davies B, Wimmi S, Diepold A. Adaptivity and dynamics in type III secretion systems. Mol Microbiol 2020; 115:395-411. [PMID: 33251695 DOI: 10.1111/mmi.14658] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Revised: 11/17/2020] [Accepted: 11/23/2020] [Indexed: 01/07/2023]
Abstract
The type III secretion system is the common core of two bacterial molecular machines: the flagellum and the injectisome. The flagellum is the most widely distributed prokaryotic locomotion device, whereas the injectisome is a syringe-like apparatus for inter-kingdom protein translocation, which is essential for virulence in important human pathogens. The successful concept of the type III secretion system has been modified for different bacterial needs. It can be adapted to changing conditions, and was found to be a dynamic complex constantly exchanging components. In this review, we highlight the flexibility, adaptivity, and dynamic nature of the type III secretion system.
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Affiliation(s)
- Bailey Milne-Davies
- Department of Ecophysiology, Max-Planck-Institute for Terrestrial Microbiology, Marburg, Germany
| | - Stephan Wimmi
- Department of Ecophysiology, Max-Planck-Institute for Terrestrial Microbiology, Marburg, Germany
| | - Andreas Diepold
- Department of Ecophysiology, Max-Planck-Institute for Terrestrial Microbiology, Marburg, Germany
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8
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Drehkopf S, Otten C, Hausner J, Seifert T, Büttner D. HrpB7 from
Xanthomonas campestris
pv.
vesicatoria
is an essential component of the type III secretion system and shares features of HrpO/FliJ/YscO family members. Cell Microbiol 2020; 22:e13160. [DOI: 10.1111/cmi.13160] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2019] [Revised: 12/16/2019] [Accepted: 12/24/2019] [Indexed: 12/22/2022]
Affiliation(s)
- Sabine Drehkopf
- Department of Genetics, Institute of BiologyMartin Luther University Halle‐Wittenberg Halle (Saale) Germany
| | - Christian Otten
- Department of Genetics, Institute of BiologyMartin Luther University Halle‐Wittenberg Halle (Saale) Germany
| | - Jens Hausner
- Department of Genetics, Institute of BiologyMartin Luther University Halle‐Wittenberg Halle (Saale) Germany
| | - Tanja Seifert
- Department of Genetics, Institute of BiologyMartin Luther University Halle‐Wittenberg Halle (Saale) Germany
| | - Daniela Büttner
- Department of Genetics, Institute of BiologyMartin Luther University Halle‐Wittenberg Halle (Saale) Germany
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Slater SL, Sågfors AM, Pollard DJ, Ruano-Gallego D, Frankel G. The Type III Secretion System of Pathogenic Escherichia coli. Curr Top Microbiol Immunol 2019; 416:51-72. [PMID: 30088147 DOI: 10.1007/82_2018_116] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Infection with enteropathogenic and enterohaemorrhagic Escherichia coli (EPEC and EHEC), enteroinvasive E. coli (EIEC) and Shigella relies on the elaboration of a type III secretion system (T3SS). Few strains also encode a second T3SS, named ETT2. Through the integration of coordinated intracellular and extracellular cues, the modular T3SS is assembled within the bacterial cell wall, as well as the plasma membrane of the host cell. As such, the T3SS serves as a conduit, allowing the chaperone-regulated translocation of effector proteins directly into the host cytosol to subvert eukaryotic cell processes. Recent technological advances revealed high structural resolution of the T3SS apparatus and how it could be exploited to treat enteric disease. This chapter summarises the current knowledge of the structure and function of the E. coli T3SSs.
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Affiliation(s)
- Sabrina L Slater
- Department of Life Sciences, MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, UK
| | - Agnes M Sågfors
- Department of Life Sciences, MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, UK
| | - Dominic J Pollard
- Department of Life Sciences, MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, UK
| | - David Ruano-Gallego
- Department of Life Sciences, MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, UK
| | - Gad Frankel
- Department of Life Sciences, MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, UK.
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Hausner J, Jordan M, Otten C, Marillonnet S, Büttner D. Modular Cloning of the Type III Secretion Gene Cluster from the Plant-Pathogenic Bacterium Xanthomonas euvesicatoria. ACS Synth Biol 2019; 8:532-547. [PMID: 30694661 DOI: 10.1021/acssynbio.8b00434] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Type III secretion (T3S) systems are essential pathogenicity factors of most Gram-negative bacteria and translocate effector proteins into plant or animal cells. T3S systems can, therefore, be used as tools for protein delivery into eukaryotic cells, for instance after transfer of the T3S gene cluster into nonpathogenic recipient strains. Here, we report the modular cloning of the T3S gene cluster from the plant-pathogenic bacterium Xanthomonas euvesicatoria. The resulting multigene construct encoded a functional T3S system and delivered effector proteins into plant cells. The modular design of the T3S gene cluster allowed the efficient replacement and rearrangement of single genes or operons and the insertion of reporter genes for functional studies. In the present study, we used the modular T3S system to analyze the assembly of a fluorescent fusion of the predicted cytoplasmic ring protein HrcQ. Our studies demonstrate the use of the modular T3S gene cluster for functional analyses and mutant approaches in X. euvesicatoria. A potential application of the modular T3S system as protein delivery tool is discussed.
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Affiliation(s)
- Jens Hausner
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Weinbergweg 10, 06120 Halle, Saale, Germany
| | - Michael Jordan
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Weinbergweg 10, 06120 Halle, Saale, Germany
| | - Christian Otten
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Weinbergweg 10, 06120 Halle, Saale, Germany
| | | | - Daniela Büttner
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Weinbergweg 10, 06120 Halle, Saale, Germany
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11
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Prochaska H, Thieme S, Daum S, Grau J, Schmidtke C, Hallensleben M, John P, Bacia K, Bonas U. A conserved motif promotes HpaB-regulated export of type III effectors from Xanthomonas. MOLECULAR PLANT PATHOLOGY 2018; 19:2473-2487. [PMID: 30073738 PMCID: PMC6638074 DOI: 10.1111/mpp.12725] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Revised: 06/07/2018] [Accepted: 06/29/2018] [Indexed: 06/08/2023]
Abstract
The type III secretion (T3S) system, an essential pathogenicity factor in most Gram-negative plant-pathogenic bacteria, injects bacterial effector proteins directly into the plant cell cytosol. Here, the type III effectors (T3Es) manipulate host cell processes to suppress defence and establish appropriate conditions for bacterial multiplication in the intercellular spaces of the plant tissue. T3E export depends on a secretion signal which is also present in 'non-effectors'. The latter are secreted extracellular components of the T3S apparatus, but are not translocated into the plant cell. How the T3S system discriminates between T3Es and non-effectors is still enigmatic. Previously, we have identified a putative translocation motif (TrM) in several T3Es from Xanthomonas campestris pv. vesicatoria (Xcv). Here, we analysed the TrM of the Xcv effector XopB in detail. Mutation studies showed that the proline/arginine-rich motif is required for efficient type III-dependent secretion and translocation of XopB and determines the dependence of XopB transport on the general T3S chaperone HpaB. Similar results were obtained for other effectors from Xcv. As the arginine residues of the TrM mediate specific binding of XopB to cardiolipin, one of the major lipid components in Xanthomonas membranes, we assume that the association of T3Es to the bacterial membrane prior to secretion supports type III-dependent export.
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Affiliation(s)
- Heike Prochaska
- Institute for Biology, Department of GeneticsMartin Luther University Halle‐WittenbergHalle (Saale)06120Germany
| | - Sabine Thieme
- Institute for Biology, Department of GeneticsMartin Luther University Halle‐WittenbergHalle (Saale)06120Germany
| | - Sebastian Daum
- Institute for Chemistry, Department of Biophysical ChemistryMartin Luther University Halle‐WittenbergHalle (Saale)06120Germany
| | - Jan Grau
- Institute for Informatics, Department of BioinformaticsMartin Luther University Halle‐WittenbergHalle (Saale)06120Germany
| | - Cornelius Schmidtke
- Institute for Biology, Department of GeneticsMartin Luther University Halle‐WittenbergHalle (Saale)06120Germany
| | - Magnus Hallensleben
- Institute for Biology, Department of GeneticsMartin Luther University Halle‐WittenbergHalle (Saale)06120Germany
| | - Peter John
- Institute for Biology, Department of GeneticsMartin Luther University Halle‐WittenbergHalle (Saale)06120Germany
| | - Kirsten Bacia
- Institute for Chemistry, Department of Biophysical ChemistryMartin Luther University Halle‐WittenbergHalle (Saale)06120Germany
| | - Ulla Bonas
- Institute for Biology, Department of GeneticsMartin Luther University Halle‐WittenbergHalle (Saale)06120Germany
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12
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Scheibner F, Hartmann N, Hausner J, Lorenz C, Hoffmeister AK, Büttner D. The Type III Secretion Chaperone HpaB Controls the Translocation of Effector and Noneffector Proteins From Xanthomonas campestris pv. vesicatoria. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2018; 31:61-74. [PMID: 28771395 DOI: 10.1094/mpmi-06-17-0138-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
Pathogenicity of the gram-negative bacterium Xanthomonas campestris pv. vesicatoria depends on a type III secretion (T3S) system, which translocates effector proteins into plant cells. Effector proteins contain N-terminal T3S and translocation signals and interact with the T3S chaperone HpaB, which presumably escorts effectors to the secretion apparatus. The molecular mechanisms underlying the recognition of effectors by the T3S system are not yet understood. In the present study, we analyzed T3S and translocation signals in the type III effectors XopE2 and XopJ from X. campestris pv. vesicatoria. Both effectors contain minimal translocation signals, which are only recognized in the absence of HpaB. Additional N-terminal signals promote translocation of XopE2 and XopJ in the wild-type strain. The results of translocation and interaction studies revealed that the interaction of XopE2 and XopJ with HpaB and a predicted cytoplasmic substrate docking site of the T3S system is not sufficient for translocation. In agreement with this finding, we show that the presence of an artificial HpaB-binding site does not promote translocation of the noneffector XopA in the wild-type strain. Our data, therefore, suggest that the T3S chaperone HpaB not only acts as an escort protein but also controls the recognition of translocation signals.
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Affiliation(s)
- Felix Scheibner
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, D-06099 Halle (Saale), Germany
| | - Nadine Hartmann
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, D-06099 Halle (Saale), Germany
| | - Jens Hausner
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, D-06099 Halle (Saale), Germany
| | - Christian Lorenz
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, D-06099 Halle (Saale), Germany
| | - Anne-Katrin Hoffmeister
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, D-06099 Halle (Saale), Germany
| | - Daniela Büttner
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, D-06099 Halle (Saale), Germany
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Blüher D, Laha D, Thieme S, Hofer A, Eschen-Lippold L, Masch A, Balcke G, Pavlovic I, Nagel O, Schonsky A, Hinkelmann R, Wörner J, Parvin N, Greiner R, Weber S, Tissier A, Schutkowski M, Lee J, Jessen H, Schaaf G, Bonas U. A 1-phytase type III effector interferes with plant hormone signaling. Nat Commun 2017; 8:2159. [PMID: 29255246 PMCID: PMC5735085 DOI: 10.1038/s41467-017-02195-8] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2017] [Accepted: 11/13/2017] [Indexed: 11/16/2022] Open
Abstract
Most Gram-negative phytopathogenic bacteria inject type III effector (T3E) proteins into plant cells to manipulate signaling pathways to the pathogen's benefit. In resistant plants, specialized immune receptors recognize single T3Es or their biochemical activities, thus halting pathogen ingress. However, molecular function and mode of recognition for most T3Es remains elusive. Here, we show that the Xanthomonas T3E XopH possesses phytase activity, i.e., dephosphorylates phytate (myo-inositol-hexakisphosphate, InsP6), the major phosphate storage compound in plants, which is also involved in pathogen defense. A combination of biochemical approaches, including a new NMR-based method to discriminate inositol polyphosphate enantiomers, identifies XopH as a naturally occurring 1-phytase that dephosphorylates InsP6 at C1. Infection of Nicotiana benthamiana and pepper by Xanthomonas results in a XopH-dependent conversion of InsP6 to InsP5. 1-phytase activity is required for XopH-mediated immunity of plants carrying the Bs7 resistance gene, and for induction of jasmonate- and ethylene-responsive genes in N. benthamiana.
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Affiliation(s)
- Doreen Blüher
- Institute for Biology, Department of Genetics, Martin-Luther University Halle-Wittenberg, Weinbergweg 10, 06120, Halle (Saale), Germany
| | - Debabrata Laha
- Institute of Crop Science and Resource Conservation, Department of Plant Nutrition, University of Bonn, Karlrobert-Kreiten-Strasse 13, 53115, Bonn, Germany
- Center for Plant Molecular Biology, Department of Plant Physiology, Eberhard Karls University Tübingen, Auf der Morgenstelle 32, 72076, Tübingen, Germany
| | - Sabine Thieme
- Institute for Biology, Department of Genetics, Martin-Luther University Halle-Wittenberg, Weinbergweg 10, 06120, Halle (Saale), Germany
| | - Alexandre Hofer
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Lennart Eschen-Lippold
- Department of Stress and Developmental Biology, Leibniz Institute of Plant Biochemistry, Weinberg 3, 06120, Halle (Saale), Germany
| | - Antonia Masch
- Institute for Biochemistry and Biotechnology, Department of Enzymology, Martin-Luther University Halle-Wittenberg, Kurt-Mothes-Strasse 3, 06120, Halle (Saale), Germany
| | - Gerd Balcke
- Department of Cell and Metabolic Biology, Leibniz Institute of Plant Biochemistry, Weinberg 3, 06120, Halle (Saale), Germany
| | - Igor Pavlovic
- Institute of Organic Chemistry, Albert-Ludwigs University Freiburg, Albertstrasse 21, 79104, Freiburg, Germany
| | - Oliver Nagel
- Institute for Biology, Department of Genetics, Martin-Luther University Halle-Wittenberg, Weinbergweg 10, 06120, Halle (Saale), Germany
| | - Antje Schonsky
- Institute for Biology, Department of Genetics, Martin-Luther University Halle-Wittenberg, Weinbergweg 10, 06120, Halle (Saale), Germany
| | - Rahel Hinkelmann
- Institute of Organic Chemistry, Albert-Ludwigs University Freiburg, Albertstrasse 21, 79104, Freiburg, Germany
| | - Jakob Wörner
- Institute of Physical Chemistry, Albert-Ludwigs University Freiburg, Albertstrasse 21, 79104, Freiburg, Germany
| | - Nargis Parvin
- Center for Plant Molecular Biology, Department of Plant Physiology, Eberhard Karls University Tübingen, Auf der Morgenstelle 32, 72076, Tübingen, Germany
| | - Ralf Greiner
- Department of Food Technology and Bioprocess Engineering, Max-Rubner-Institut, Federal Research Institute of Nutrition and Food, Haid-und-Neu-Straße 9, 76131, Karlsruhe, Germany
| | - Stefan Weber
- Institute of Physical Chemistry, Albert-Ludwigs University Freiburg, Albertstrasse 21, 79104, Freiburg, Germany
| | - Alain Tissier
- Department of Cell and Metabolic Biology, Leibniz Institute of Plant Biochemistry, Weinberg 3, 06120, Halle (Saale), Germany
| | - Mike Schutkowski
- Institute for Biochemistry and Biotechnology, Department of Enzymology, Martin-Luther University Halle-Wittenberg, Kurt-Mothes-Strasse 3, 06120, Halle (Saale), Germany
| | - Justin Lee
- Department of Stress and Developmental Biology, Leibniz Institute of Plant Biochemistry, Weinberg 3, 06120, Halle (Saale), Germany
| | - Henning Jessen
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
- Institute of Organic Chemistry, Albert-Ludwigs University Freiburg, Albertstrasse 21, 79104, Freiburg, Germany.
| | - Gabriel Schaaf
- Institute of Crop Science and Resource Conservation, Department of Plant Nutrition, University of Bonn, Karlrobert-Kreiten-Strasse 13, 53115, Bonn, Germany.
- Center for Plant Molecular Biology, Department of Plant Physiology, Eberhard Karls University Tübingen, Auf der Morgenstelle 32, 72076, Tübingen, Germany.
| | - Ulla Bonas
- Institute for Biology, Department of Genetics, Martin-Luther University Halle-Wittenberg, Weinbergweg 10, 06120, Halle (Saale), Germany.
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Scheibner F, Marillonnet S, Büttner D. The TAL Effector AvrBs3 from Xanthomonas campestris pv. vesicatoria Contains Multiple Export Signals and Can Enter Plant Cells in the Absence of the Type III Secretion Translocon. Front Microbiol 2017; 8:2180. [PMID: 29170655 PMCID: PMC5684485 DOI: 10.3389/fmicb.2017.02180] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2017] [Accepted: 10/24/2017] [Indexed: 12/27/2022] Open
Abstract
Pathogenicity of the Gram-negative plant-pathogenic bacterium Xanthomonas campestris pv. vesicatoria depends on a type III secretion (T3S) system which translocates effector proteins into plant cells. Effector protein delivery is controlled by the T3S chaperone HpaB, which presumably escorts effector proteins to the secretion apparatus. One intensively studied effector is the transcription activator-like (TAL) effector AvrBs3, which binds to promoter sequences of plant target genes and activates plant gene expression. It was previously reported that type III-dependent delivery of AvrBs3 depends on the N-terminal protein region. The signals that control T3S and translocation of AvrBs3, however, have not yet been characterized. In the present study, we show that T3S and translocation of AvrBs3 depend on the N-terminal 10 and 50 amino acids, respectively. Furthermore, we provide experimental evidence that additional signals in the N-terminal 30 amino acids and the region between amino acids 64 and 152 promote translocation of AvrBs3 in the absence of HpaB. Unexpectedly, in vivo translocation assays revealed that AvrBs3 is delivered into plant cells even in the absence of HrpF, which is the predicted channel-forming component of the T3S translocon in the plant plasma membrane. The presence of HpaB- and HrpF-independent transport routes suggests that the delivery of AvrBs3 is initiated during early stages of the infection process, presumably before the activation of HpaB or the insertion of the translocon into the plant plasma membrane.
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Affiliation(s)
- Felix Scheibner
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Halle, Germany
| | | | - Daniela Büttner
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Halle, Germany
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15
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Abendroth U, Adlung N, Otto A, Grüneisen B, Becher D, Bonas U. Identification of new protein-coding genes with a potential role in the virulence of the plant pathogen Xanthomonas euvesicatoria. BMC Genomics 2017; 18:625. [PMID: 28814272 PMCID: PMC5559785 DOI: 10.1186/s12864-017-4041-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2017] [Accepted: 08/08/2017] [Indexed: 01/08/2023] Open
Abstract
Background Bacteria of the genus Xanthomonas are economically important plant pathogens. Pathogenicity of Xanthomonas spp. depends on the type III-secretion system and additional virulence determinants. The number of sequenced Xanthomonas genomes increases rapidly, however, accurate annotation of these genomes is difficult, because it relies on gene prediction programs. In this study, we used a mass-spectrometry (MS)-based approach to identify the proteome of Xanthomonas euvesicatoria (Xe) strain 85–10 also known as X. campestris pv. vesicatoria, a well-studied member of plant-pathogenic Xanthomonadaceae. Results Using different culture conditions, MS-datasets were searched against a six-frame-translated genome database of Xe. In total, we identified 2588 proteins covering 55% of the Xe genome, including 764 hitherto hypothetical proteins. Our proteogenomic approach identified 30 new protein-coding genes and allowed correction of the N-termini of 50 protein-coding genes. For five novel and two N-terminally corrected genes the corresponding proteins were confirmed by immunoblot. Furthermore, our data indicate that two putative type VI-secretion systems encoded in Xe play no role in bacterial virulence which was experimentally confirmed. Conclusions The discovery and re-annotation of numerous genes in the genome of Xe shows that also a well-annotated genome can be improved. Additionally, our proteogenomic analyses validates “hypothetical” proteins and will improve annotation of Xanthomonadaceae genomes, providing a solid basis for further studies. Electronic supplementary material The online version of this article (doi:10.1186/s12864-017-4041-7) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Ulrike Abendroth
- Institute for Biology, Department of Genetics, Martin-Luther-Universität Halle-Wittenberg, D-06099, Halle, Germany.
| | - Norman Adlung
- Institute for Biology, Department of Genetics, Martin-Luther-Universität Halle-Wittenberg, D-06099, Halle, Germany
| | - Andreas Otto
- Institute for Microbiology, Department of Mass Spectrometry, Ernst-Moritz-Arndt-Universität, D-17487, Greifswald, Germany
| | - Benjamin Grüneisen
- Institute for Biology, Department of Genetics, Martin-Luther-Universität Halle-Wittenberg, D-06099, Halle, Germany.,Department of Psychiatry and Psychotherapy, Martin-Luther-Universität Halle-Wittenberg, D-06097, Halle, Germany
| | - Dörte Becher
- Institute for Microbiology, Department of Mass Spectrometry, Ernst-Moritz-Arndt-Universität, D-17487, Greifswald, Germany
| | - Ulla Bonas
- Institute for Biology, Department of Genetics, Martin-Luther-Universität Halle-Wittenberg, D-06099, Halle, Germany.
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16
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Pesce C, Jacobs JM, Berthelot E, Perret M, Vancheva T, Bragard C, Koebnik R. Comparative Genomics Identifies a Novel Conserved Protein, HpaT, in Proteobacterial Type III Secretion Systems that Do Not Possess the Putative Translocon Protein HrpF. Front Microbiol 2017; 8:1177. [PMID: 28694803 PMCID: PMC5483457 DOI: 10.3389/fmicb.2017.01177] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2017] [Accepted: 06/09/2017] [Indexed: 01/09/2023] Open
Abstract
Xanthomonas translucens is the causal agent of bacterial leaf streak, the most common bacterial disease of wheat and barley. To cause disease, most xanthomonads depend on a highly conserved type III secretion system, which translocates type III effectors into host plant cells. Mutagenesis of the conserved type III secretion gene hrcT confirmed that the X. translucens type III secretion system is required to cause disease on the host plant barley and to trigger a non-host hypersensitive response (HR) in pepper leaves. Type III effectors are delivered to the host cell by a surface appendage, the Hrp pilus, and a translocon protein complex that inserts into the plant cell plasma membrane. Homologs of the Xanthomonas HrpF protein, including PopF from Ralstonia solanacearum and NolX from rhizobia, are thought to act as a translocon protein. Comparative genomics revealed that X. translucens strains harbor a noncanonical hrp gene cluster, which rather shares features with type III secretion systems from Ralstonia solanacearum, Paraburkholderia andropogonis, Collimonas fungivorans, and Uliginosibacterium gangwonense than other Xanthomonas spp. Surprisingly, none of these bacteria, except R. solanacearum, encode a homolog of the HrpF translocon. Here, we aimed at identifying a candidate translocon from X. translucens. Notably, genomes from strains that lacked hrpF/popF/nolX instead encode another gene, called hpaT, adjacent to and co-regulated with the type III secretion system gene cluster. An insertional mutant in the X. translucens hpaT gene, which is the first gene of a two-gene operon, hpaT-hpaH, was non-pathogenic on barley and did not cause the HR or programmed cell death in non-host pepper similar to the hrcT mutant. The hpaT mutant phenotypes were partially complemented by either hpaT or the downstream gene, hpaH, which has been described as a facilitator of translocation in Xanthomonas oryzae. Interestingly, the hpaT mutant was also complemented by the hrpF gene from Xanthomonas euvesicatoria. These findings reveal that both HpaT and HpaH contribute to the injection of type III effectors into plant cells.
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Affiliation(s)
- Céline Pesce
- UMR 186 IRD-Cirad-Université Montpellier IPMEMontpellier, France
- Applied Microbiology Phytopathology, Earth and Life Institute, Université catholique de LouvainLouvain-la-Neuve, Belgium
| | - Jonathan M. Jacobs
- UMR 186 IRD-Cirad-Université Montpellier IPMEMontpellier, France
- Applied Microbiology Phytopathology, Earth and Life Institute, Université catholique de LouvainLouvain-la-Neuve, Belgium
| | - Edwige Berthelot
- UMR 186 IRD-Cirad-Université Montpellier IPMEMontpellier, France
| | - Marion Perret
- UMR 186 IRD-Cirad-Université Montpellier IPMEMontpellier, France
| | - Taca Vancheva
- UMR 186 IRD-Cirad-Université Montpellier IPMEMontpellier, France
- Applied Microbiology Phytopathology, Earth and Life Institute, Université catholique de LouvainLouvain-la-Neuve, Belgium
| | - Claude Bragard
- Applied Microbiology Phytopathology, Earth and Life Institute, Université catholique de LouvainLouvain-la-Neuve, Belgium
| | - Ralf Koebnik
- UMR 186 IRD-Cirad-Université Montpellier IPMEMontpellier, France
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17
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Hausner J, Hartmann N, Jordan M, Büttner D. The Predicted Lytic Transglycosylase HpaH from Xanthomonas campestris pv. vesicatoria Associates with the Type III Secretion System and Promotes Effector Protein Translocation. Infect Immun 2017; 85:e00788-16. [PMID: 27895129 PMCID: PMC5278175 DOI: 10.1128/iai.00788-16] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Accepted: 11/20/2016] [Indexed: 02/08/2023] Open
Abstract
The pathogenicity of the Gram-negative plant-pathogenic bacterium Xanthomonas campestris pv. vesicatoria depends on a type III secretion (T3S) system, which spans both bacterial membranes and translocates effector proteins into plant cells. The assembly of the T3S system presumably involves the predicted lytic transglycosylase (LT) HpaH, which is encoded adjacent to the T3S gene cluster. Bacterial LTs degrade peptidoglycan and often promote the formation of membrane-spanning macromolecular protein complexes. In the present study, we show that HpaH localizes to the bacterial periplasm and binds to peptidoglycan as well as to components of the T3S system, including the predicted periplasmic inner rod proteins HrpB1 and HrpB2 as well as the pilus protein HrpE. In vivo translocation assays revealed that HpaH promotes the translocation of various effector proteins and of early substrates of the T3S system, suggesting a general contribution of HpaH to type III-dependent protein export. Mutant studies and the analysis of reporter fusions showed that the N-terminal region of HpaH contributes to protein function and is proteolytically cleaved. The N-terminally truncated HpaH cleavage product is secreted into the extracellular milieu by a yet-unknown transport pathway, which is independent of the T3S system.
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Affiliation(s)
- Jens Hausner
- Institute of Biology, Genetics Department, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Nadine Hartmann
- Institute of Biology, Genetics Department, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Michael Jordan
- Institute of Biology, Genetics Department, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Daniela Büttner
- Institute of Biology, Genetics Department, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
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18
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Gaytán MO, Martínez-Santos VI, Soto E, González-Pedrajo B. Type Three Secretion System in Attaching and Effacing Pathogens. Front Cell Infect Microbiol 2016; 6:129. [PMID: 27818950 PMCID: PMC5073101 DOI: 10.3389/fcimb.2016.00129] [Citation(s) in RCA: 115] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2016] [Accepted: 09/27/2016] [Indexed: 02/06/2023] Open
Abstract
Enteropathogenic Escherichia coli and enterohemorrhagic E. coli are diarrheagenic bacterial human pathogens that cause severe gastroenteritis. These enteric pathotypes, together with the mouse pathogen Citrobacter rodentium, belong to the family of attaching and effacing pathogens that form a distinctive histological lesion in the intestinal epithelium. The virulence of these bacteria depends on a type III secretion system (T3SS), which mediates the translocation of effector proteins from the bacterial cytosol into the infected cells. The core architecture of the T3SS consists of a multi-ring basal body embedded in the bacterial membranes, a periplasmic inner rod, a transmembrane export apparatus in the inner membrane, and cytosolic components including an ATPase complex and the C-ring. In addition, two distinct hollow appendages are assembled on the extracellular face of the basal body creating a channel for protein secretion: an approximately 23 nm needle, and a filament that extends up to 600 nm. This filamentous structure allows these pathogens to get through the host cells mucus barrier. Upon contact with the target cell, a translocation pore is assembled in the host membrane through which the effector proteins are injected. Assembly of the T3SS is strictly regulated to ensure proper timing of substrate secretion. The different type III substrates coexist in the bacterial cytoplasm, and their hierarchical secretion is determined by specialized chaperones in coordination with two molecular switches and the so-called sorting platform. In this review, we present recent advances in the understanding of the T3SS in attaching and effacing pathogens.
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Affiliation(s)
- Meztlli O Gaytán
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México Ciudad de México, Mexico
| | - Verónica I Martínez-Santos
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México Ciudad de México, Mexico
| | - Eduardo Soto
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México Ciudad de México, Mexico
| | - Bertha González-Pedrajo
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México Ciudad de México, Mexico
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Scheibner F, Schulz S, Hausner J, Marillonnet S, Büttner D. Type III-Dependent Translocation of HrpB2 by a Nonpathogenic hpaABC Mutant of the Plant-Pathogenic Bacterium Xanthomonas campestris pv. vesicatoria. Appl Environ Microbiol 2016; 82:3331-3347. [PMID: 27016569 PMCID: PMC4959247 DOI: 10.1128/aem.00537-16] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Accepted: 03/21/2016] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED The plant-pathogenic bacterium Xanthomonas campestris pv. vesicatoria employs a type III secretion (T3S) system to translocate effector proteins into plant cells. The T3S apparatus spans both bacterial membranes and is associated with an extracellular pilus and a channel-like translocon in the host plasma membrane. T3S is controlled by the switch protein HpaC, which suppresses secretion and translocation of the predicted inner rod protein HrpB2 and promotes secretion of translocon and effector proteins. We previously reported that HrpB2 interacts with HpaC and the cytoplasmic domain of the inner membrane protein HrcU (C. Lorenz, S. Schulz, T. Wolsch, O. Rossier, U. Bonas, and D. Büttner, PLoS Pathog 4:e1000094, 2008, http://dx.doi.org/10.1371/journal.ppat.1000094). However, the molecular mechanisms underlying the control of HrpB2 secretion are not yet understood. Here, we located a T3S and translocation signal in the N-terminal 40 amino acids of HrpB2. The results of complementation experiments with HrpB2 deletion derivatives revealed that the T3S signal of HrpB2 is essential for protein function. Furthermore, interaction studies showed that the N-terminal region of HrpB2 interacts with the cytoplasmic domain of HrcU, suggesting that the T3S signal of HrpB2 contributes to substrate docking. Translocation of HrpB2 is suppressed not only by HpaC but also by the T3S chaperone HpaB and its secreted regulator, HpaA. Deletion of hpaA, hpaB, and hpaC leads to a loss of pathogenicity but allows the translocation of fusion proteins between the HrpB2 T3S signal and effector proteins into leaves of host and non-host plants. IMPORTANCE The T3S system of the plant-pathogenic bacterium Xanthomonas campestris pv. vesicatoria is essential for pathogenicity and delivers effector proteins into plant cells. T3S depends on HrpB2, which is a component of the predicted periplasmic inner rod structure of the secretion apparatus. HrpB2 is secreted during the early stages of the secretion process and interacts with the cytoplasmic domain of the inner membrane protein HrcU. Here, we localized the secretion and translocation signal of HrpB2 in the N-terminal 40 amino acids and show that this region is sufficient for the interaction with the cytoplasmic domain of HrcU. Our results suggest that the T3S signal of HrpB2 is required for the docking of HrpB2 to the secretion apparatus. Furthermore, we provide experimental evidence that the N-terminal region of HrpB2 is sufficient to target effector proteins for translocation in a nonpathogenic X. campestris pv. vesicatoria strain.
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Affiliation(s)
- Felix Scheibner
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Steve Schulz
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Jens Hausner
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | | | - Daniela Büttner
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
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20
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McNally RR, Zeng Q, Sundin GW. HrcU and HrpP are pathogenicity factors in the fire blight pathogen Erwinia amylovora required for the type III secretion of DspA/E. BMC Microbiol 2016; 16:88. [PMID: 27206522 PMCID: PMC4875606 DOI: 10.1186/s12866-016-0702-y] [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: 09/02/2015] [Accepted: 05/10/2016] [Indexed: 11/19/2022] Open
Abstract
Background Many Gram-negative bacterial pathogens mediate host-microbe interactions via utilization of the type III secretion (T3S) system. The T3S system is a complex molecular machine consisting of more than 20 proteins. Collectively, these proteins translocate effectors across extracellular space and into the host cytoplasm. Successful translocation requires timely synthesis and allocation of both structural and secreted T3S proteins. Based on amino acid conservation in animal pathogenic bacteria, HrcU and HrpP were examined for their roles in regulation of T3S hierarchy. Results Both HrcU and HrpP were shown to be required for disease development in an immature pear infection model and respective mutants were unable to induce a hypersensitive response in tobacco. Using in vitro western blot analyses, both proteins were also shown to be required for the secretion of DspA/E, a type 3 effector and an important pathogenicity factor. Via yeast-two hybridization (Y2H), HrpP and HrcU were revealed to exhibit protein-protein binding. Finally, all HrcU and HrpP phenotypes identified were shown to be dependent on a conserved amino acid motif in the cytoplasmic tail of HrcU. Conclusions Collectively, these data demonstrate roles for HrcU and HrpP in regulating T3S and represent the first attempt in understanding T3S heirarchy in E. amylovora. Electronic supplementary material The online version of this article (doi:10.1186/s12866-016-0702-y) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- R Ryan McNally
- Department of Plant Pathology, University of Minnesota, St. Paul, MN, 55108, USA.,Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, MI, 48824, USA
| | - Quan Zeng
- Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, MI, 48824, USA.,Department of Plant Pathology and Ecology, Connecticut Agricultural Experiment Station, New Haven, CT, 06504, USA
| | - George W Sundin
- Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, MI, 48824, USA.
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21
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Xanthomonas campestris pv. vesicatoria Secretes Proteases and Xylanases via the Xps Type II Secretion System and Outer Membrane Vesicles. J Bacteriol 2015; 197:2879-93. [PMID: 26124239 DOI: 10.1128/jb.00322-15] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Accepted: 06/19/2015] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED Many plant-pathogenic bacteria utilize type II secretion (T2S) systems to secrete degradative enzymes into the extracellular milieu. T2S substrates presumably mediate the degradation of plant cell wall components during the host-pathogen interaction and thus promote bacterial virulence. Previously, the Xps-T2S system from Xanthomonas campestris pv. vesicatoria was shown to contribute to extracellular protease activity and the secretion of a virulence-associated xylanase. The identities and functions of additional T2S substrates from X. campestris pv. vesicatoria, however, are still unknown. In the present study, the analysis of 25 candidate proteins from X. campestris pv. vesicatoria led to the identification of two type II secreted predicted xylanases, a putative protease and a lipase which was previously identified as a virulence factor of X. campestris pv. vesicatoria. Studies with mutant strains revealed that the identified xylanases and the protease contribute to virulence and in planta growth of X. campestris pv. vesicatoria. When analyzed in the related pathogen X. campestris pv. campestris, several T2S substrates from X. campestris pv. vesicatoria were secreted independently of the T2S systems, presumably because of differences in the T2S substrate specificities of the two pathogens. Furthermore, in X. campestris pv. vesicatoria T2S mutants, secretion of T2S substrates was not completely absent, suggesting the contribution of additional transport systems to protein secretion. In line with this hypothesis, T2S substrates were detected in outer membrane vesicles, which were frequently observed for X. campestris pv. vesicatoria. We, therefore, propose that extracellular virulence-associated enzymes from X. campestris pv. vesicatoria are targeted to the Xps-T2S system and to outer membrane vesicles. IMPORTANCE The virulence of plant-pathogenic bacteria often depends on TS2 systems, which secrete degradative enzymes into the extracellular milieu. T2S substrates are being studied in several plant-pathogenic bacteria, including Xanthomonas campestris pv. vesicatoria, which causes bacterial spot disease in tomato and pepper. Here, we show that the T2S system from X. campestris pv. vesicatoria secretes virulence-associated xylanases, a predicted protease, and a lipase. Secretion assays with the related pathogen X. campestris pv. campestris revealed important differences in the T2S substrate specificities of the two pathogens. Furthermore, electron microscopy showed that T2S substrates from X. campestris pv. vesicatoria are targeted to outer membrane vesicles (OMVs). Our results, therefore, suggest that OMVs provide an alternative transport route for type II secreted extracellular enzymes.
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Andrade MO, Farah CS, Wang N. The post-transcriptional regulator rsmA/csrA activates T3SS by stabilizing the 5' UTR of hrpG, the master regulator of hrp/hrc genes, in Xanthomonas. PLoS Pathog 2014; 10:e1003945. [PMID: 24586158 PMCID: PMC3937308 DOI: 10.1371/journal.ppat.1003945] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2013] [Accepted: 01/09/2014] [Indexed: 11/28/2022] Open
Abstract
The RsmA/CsrA family of the post-transcriptional regulators of bacteria is involved in the regulation of many cellular processes, including pathogenesis. In this study, we demonstrated that rsmA not only is required for the full virulence of the phytopathogenic bacterium Xanthomonas citri subsp. citri (XCC) but also contributes to triggering the hypersensitive response (HR) in non-host plants. Deletion of rsmA resulted in significantly reduced virulence in the host plant sweet orange and a delayed and weakened HR in the non-host plant Nicotiana benthamiana. Microarray, quantitative reverse-transcription PCR, western-blotting, and GUS assays indicated that RsmA regulates the expression of the type 3 secretion system (T3SS) at both transcriptional and post-transcriptional levels. The regulation of T3SS by RsmA is a universal phenomenon in T3SS-containing bacteria, but the specific mechanism seems to depend on the interaction between a particular bacterium and its hosts. For Xanthomonads, the mechanism by which RsmA activates T3SS remains unknown. Here, we show that RsmA activates the expression of T3SS-encoding hrp/hrc genes by directly binding to the 5′ untranslated region (UTR) of hrpG, the master regulator of the hrp/hrc genes in XCC. RsmA stabilizes hrpG mRNA, leading to increased accumulation of HrpG proteins and subsequently, the activation of hrp/hrc genes. The activation of the hrp/hrc genes by RsmA via HrpG was further supported by the observation that ectopic overexpression of hrpG in an rsmA mutant restored its ability to cause disease in host plants and trigger HR in non-host plants. RsmA also stabilizes the transcripts of another T3SS-associated hrpD operon by directly binding to the 5′ UTR region. Taken together, these data revealed that RsmA primarily activates T3SS by acting as a positive regulator of hrpG and that this regulation is critical to the pathogenicity of XCC. Pathogenic bacteria demonstrate sophisticated capacity to regulate gene expression to meet requirements of living in different environmental niches, including in the hosts. The activation of the Type 3 secretion system (T3SS) genes in response to the host enviroment is under the control of several factors, such as the post-transcriptional regulator RsmA/CsrA. Here, we show that RsmA contributes to the pathogenicity of Xanthomonas citri in host plants and the HR-triggering activity in non-host plants by regulating the expression of T3SS-encoding hrp/hrc genes. RsmA directly interacts with the 5′ UTRs of hrpG and hrpD mRNAs, which leads to increased HrpG protein levels by stabilizing the hrpG transcript. Further, overexpression of hrpG in an rsmA mutant restored its pathogenicity and ability to cause HR. The deletion of rsmA did not affect the phosphorylation of HrpG, which is also required for T3SS activation. This work provides mechanistic insights for the first time into RsmA-mediated regulation of T3SS gene expression by acting as a positive regulator of hrpG at the post-transcription level.
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Affiliation(s)
- Maxuel O. Andrade
- Citrus Research and Education Center, Department of Microbiology and Cell Sciences, University of Florida, Lake Alfred, Florida, United States of America
| | - Chuck S. Farah
- Department of Biochemistry, Institute of Chemistry, University of São Paulo, São Paulo, São Paulo, Brazil
| | - Nian Wang
- Citrus Research and Education Center, Department of Microbiology and Cell Sciences, University of Florida, Lake Alfred, Florida, United States of America
- * E-mail:
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Hausner J, Büttner D. The YscU/FlhB homologue HrcU from Xanthomonas controls type III secretion and translocation of early and late substrates. MICROBIOLOGY-SGM 2014; 160:576-588. [PMID: 24425767 DOI: 10.1099/mic.0.075176-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The majority of Gram-negative plant- and animal-pathogenic bacteria employ a type III secretion (T3S) system to deliver effector proteins to eukaryotic cells. Members of the YscU protein family are essential components of the T3S system and consist of a transmembrane and a cytoplasmic region that is autocatalytically cleaved at a conserved NPTH motif. YscU homologues interact with T3S substrate specificity switch (T3S4) proteins that alter the substrate specificity of the T3S system after assembly of the secretion apparatus. We previously showed that the YscU homologue HrcU from the plant pathogen Xanthomonas campestris pv. vesicatoria interacts with the T3S4 protein HpaC and is required for the secretion of translocon and effector proteins. In the present study, analysis of HrcU deletion, insertion and point mutant derivatives led to the identification of amino acid residues in the cytoplasmic region of HrcU (HrcUC) that control T3S and translocation of the predicted inner rod protein HrpB2, the translocon protein HrpF and the effector protein AvrBs3. Mutations in the vicinity of the NPTH motif interfered with HrcU cleavage and/or the interaction of HrcUC with HrpB2 and the T3S4 protein HpaC. However, HrcU function was not completely abolished, suggesting that HrcU cleavage is not crucial for pathogenicity and T3S. Given that mutations in HrcU differentially affected T3S and translocation of HrpB2 and effector proteins, we propose that HrcU controls the secretion of different T3S substrate classes by independent mechanisms.
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Affiliation(s)
- Jens Hausner
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Weinbergweg 10, 06120 Halle (Saale), Germany
| | - Daniela Büttner
- Institute of Biology, Department of Genetics, Martin Luther University Halle-Wittenberg, Weinbergweg 10, 06120 Halle (Saale), Germany
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Chang JH, Desveaux D, Creason AL. The ABCs and 123s of bacterial secretion systems in plant pathogenesis. ANNUAL REVIEW OF PHYTOPATHOLOGY 2014; 52:317-45. [PMID: 24906130 DOI: 10.1146/annurev-phyto-011014-015624] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Bacteria have many export and secretion systems that translocate cargo into and across biological membranes. Seven secretion systems contribute to pathogenicity by translocating proteinaceous cargos that can be released into the extracellular milieu or directly into recipient cells. In this review, we describe these secretion systems and how their complexities and functions reflect differences in the destinations, states, functions, and sizes of the translocated cargos as well as the architecture of the bacterial cell envelope. We examine the secretion systems from the perspective of pathogenic bacteria that proliferate within plant tissues and highlight examples of translocated proteins that contribute to the infection and disease of plant hosts.
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Affiliation(s)
- Jeff H Chang
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331; ,
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25
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Hartmann N, Büttner D. The inner membrane protein HrcV from Xanthomonas spp. is involved in substrate docking during type III secretion. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2013; 26:1176-1189. [PMID: 23777429 DOI: 10.1094/mpmi-01-13-0019-r] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Pathogenicity of the gram-negative plant-pathogenic bacterium Xanthomonas campestris pv. vesicatoria depends on a membrane-spanning type III secretion (T3S) system, which translocates effector proteins into eukaryotic host cells. In this study, we characterized the T3S system component HrcV, which is a member of the YscV/FlhA family of inner membrane proteins. HrcV consists of eight transmembrane helices and a cytoplasmic region (HrcVC). Mutant and protein-protein interaction studies showed that HrcVC is essential for protein function and binds to T3S substrates, including the early substrate HrpB2, the pilus protein HrpE, and effector proteins. Furthermore, HrcVC interacts with itself and with components and control proteins of the T3S apparatus. The interaction of HrcVC with HrpB2, HrpE, and T3S system components depends on amino acid residues in a conserved motif, designated flagella/hypersensitive response/invasion proteins export pore (FHIPEP), which is located in a cytoplasmic loop between transmembrane helix four and five of HrcV. Mutations in the FHIPEP motif abolish HrcV function but do not affect the interaction of HrcVC with effector proteins.
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26
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Hausner J, Hartmann N, Lorenz C, Büttner D. The periplasmic HrpB1 protein from Xanthomonas spp. binds to peptidoglycan and to components of the type III secretion system. Appl Environ Microbiol 2013; 79:6312-24. [PMID: 23934485 PMCID: PMC3811196 DOI: 10.1128/aem.01226-13] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2013] [Accepted: 07/31/2013] [Indexed: 11/20/2022] Open
Abstract
The plant-pathogenic bacterium Xanthomonas campestris pv. vesicatoria employs a type III secretion (T3S) system to translocate bacterial effector proteins into eukaryotic host cells. The membrane-spanning secretion apparatus consists of 11 core components and several associated proteins with yet unknown functions. In this study, we analyzed the role of HrpB1, which was previously shown to be essential for T3S and the formation of the extracellular T3S pilus. We provide experimental evidence that HrpB1 localizes to the bacterial periplasm and binds to peptidoglycan, which is in agreement with its predicted structural similarity to the putative peptidoglycan-binding domain of the lytic transglycosylase Slt70 from Escherichia coli. Interaction studies revealed that HrpB1 forms protein complexes and binds to T3S system components, including the inner membrane protein HrcD, the secretin HrcC, the pilus protein HrpE, and the putative inner rod protein HrpB2. The analysis of deletion and point mutant derivatives of HrpB1 led to the identification of amino acid residues that contribute to the interaction of HrpB1 with itself and HrcD and/or to protein function. The finding that HrpB1 and HrpB2 colocalize to the periplasm and both interact with HrcD suggests that they are part of a periplasmic substructure of the T3S system.
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Affiliation(s)
- Jens Hausner
- Institute of Biology, Department of Genetics, Martin-Luther University Halle-Wittenberg, Halle (Saale), Germany
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