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Hotson A, Chosed R, Shu H, Orth K, Mudgett MB. Xanthomonas type III effector XopD targets SUMO-conjugated proteins in planta. Mol Microbiol 2004; 50:377-89. [PMID: 14617166 DOI: 10.1046/j.1365-2958.2003.03730.x] [Citation(s) in RCA: 217] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Xanthomonas campestris pathovar vesicatoria (Xcv) uses the type III secretion system (TTSS) to inject effector proteins into cells of Solanaceous plants during pathogenesis. A number of Xcv TTSS effectors have been identified; however, their function in planta remains elusive. Here, we provide direct evidence for a functional role for a phytopathogenic bacterial TTSS effector in planta by demonstrating that the Xcv effector XopD encodes an active cysteine protease with plant-specific SUMO substrate specificity. XopD is injected into plant cells by the TTSS during Xcv pathogenesis, translocated to subnuclear foci and hydrolyses SUMO-conjugated proteins in vivo. Our studies suggest that XopD mimics endogenous plant SUMO isopeptidases to interfere with the regulation of host proteins during Xcv infection.
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Affiliation(s)
- Andrew Hotson
- Department of Biological Sciences, Stanford University, Stanford, CA 94305-5020, USA
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102
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Büttner D, Noël L, Thieme F, Bonas U. Genomic approaches in Xanthomonas campestris pv. vesicatoria allow fishing for virulence genes. J Biotechnol 2004; 106:203-14. [PMID: 14651862 DOI: 10.1016/j.jbiotec.2003.07.012] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Xanthomonas campestris pv. vesicatoria is an economically important pathogen of pepper and tomato and has been established as a model organism to study bacterial infection strategies. In the last two decades, intensive genetic and molecular analyses led to the isolation of many genes that play a role in the intimate molecular relationship with the host plant. Essential for pathogenicity is a type III protein secretion system, which delivers bacterial effector proteins into the host cell. Currently, the genome of X. campestris pv. vesicatoria is being sequenced. The availability of genomic sequence information will pave the way for the identification of new bacterial virulence factors by bioinformatic approaches. In this article, we will present preliminary data from the genomic sequence analysis and describe recent and novel studies to identify bacterial type III effector genes.
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Affiliation(s)
- Daniela Büttner
- Institut für Genetik, Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle(Saale), Germany
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103
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Wehling MD, Guo M, Fu ZQ, Alfano JR. The Pseudomonas syringae HopPtoV protein is secreted in culture and translocated into plant cells via the type III protein secretion system in a manner dependent on the ShcV type III chaperone. J Bacteriol 2004; 186:3621-30. [PMID: 15150250 PMCID: PMC415770 DOI: 10.1128/jb.186.11.3621-3630.2004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2003] [Accepted: 02/11/2004] [Indexed: 12/27/2022] Open
Abstract
The bacterial plant pathogen Pseudomonas syringae depends on a type III protein secretion system and the effector proteins that it translocates into plant cells to cause disease and to elicit the defense-associated hypersensitive response on resistant plants. The availability of the P. syringae pv. tomato DC3000 genome sequence has resulted in the identification of many novel effectors. We identified the hopPtoV effector gene on the basis of its location next to a candidate type III chaperone (TTC) gene, shcV, and within a pathogenicity island in the DC3000 chromosome. A DC3000 mutant lacking ShcV was unable to secrete detectable amounts of HopPtoV into culture supernatants or translocate HopPtoV into plant cells, based on an assay that tested whether HopPtoV-AvrRpt2 fusions were delivered into plant cells. Coimmunoprecipitation and Saccharomyces cerevisiae two-hybrid experiments showed that ShcV and HopPtoV interact directly with each other. The ShcV binding site was delimited to an N-terminal region of HopPtoV between amino acids 76 and 125 of the 391-residue full-length protein. Our results demonstrate that ShcV is a TTC for the HopPtoV effector. DC3000 overexpressing ShcV and HopPtoV and DC3000 mutants lacking either HopPtoV or both ShcV and HopPtoV were not significantly impaired in disease symptoms or bacterial multiplication in planta, suggesting that HopPtoV plays a subtle role in pathogenesis or that other effectors effectively mask the contribution of HopPtoV in plant pathogenesis.
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Affiliation(s)
- Misty D Wehling
- Plant Science Initiative and Department of Pathology, University of Nebraska, Lincoln, Nebraska 68588-0660, USA
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104
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Roden J, Eardley L, Hotson A, Cao Y, Mudgett MB. Characterization of the Xanthomonas AvrXv4 effector, a SUMO protease translocated into plant cells. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2004; 17:633-43. [PMID: 15195946 DOI: 10.1094/mpmi.2004.17.6.633] [Citation(s) in RCA: 108] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Homologs of the Yersinia virulence factor YopJ are found in both animal and plant bacterial pathogens, as well as in plant symbionts. The conservation of this effector family indicates that several pathogens may use YopJ-like proteins to regulate bacteria-host interactions during infection. YopJ and YopJ-like proteins share structural homology with cysteine proteases and are hypothesized to functionally mimic small ubiquitin-like modifier (SUMO) proteases in eukaryotic cells. Strains of the phytopathogenic bacterium Xanthomonas campestris pv. vesicatoria are known to possess four YopJ-like proteins, AvrXv4, AvrBsT, AvrRxv, and XopJ. In this work, we have characterized AvrXv4 to determine if AvrXv4 functions like a SUMO protease in planta during Xanthomonas-plant interactions. We provide evidence that X. campestris pv. vesicatoria secretes and translocates the AvrXv4 protein into plant cells during infection in a type III-dependent manner. Once inside the plant cell, AvrXv4 is localized to the plant cytoplasm. By performing AvrXv4 deletion and mutational analysis, we have identified amino acids required for type III delivery and for host recognition. We show that AvrXv4 recognition by resistant plants requires a functional protease catalytic core, the domain that is conserved in all of the putative YopJ-like cysteine proteases. We also show that AvrXv4 expression in planta leads to a reduction in SUMO-modified proteins, demonstrating that AvrXv4 possesses SUMO isopeptidase activity. Overall, our studies reveal that the YopJ-like effector AvrXv4 encodes a type III SUMO protease effector that is active in the cytoplasmic compartment of plant cells.
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Affiliation(s)
- Julie Roden
- Department of Biological Sciences, Stanford University, Stanford, CA 94305, USA
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105
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Cunnac S, Boucher C, Genin S. Characterization of the cis-acting regulatory element controlling HrpB-mediated activation of the type III secretion system and effector genes in Ralstonia solanacearum. J Bacteriol 2004; 186:2309-18. [PMID: 15060033 PMCID: PMC412162 DOI: 10.1128/jb.186.8.2309-2318.2004] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The ability of Ralstonia solanacearum to cause disease on plants depends on its type III secretion system (TTSS) encoded by hrp genes. The expression of hrp genes and known TTSS substrates is coordinately regulated by HrpB, a member of the AraC family of transcriptional regulators. Two HrpB-regulated promoters (hrpY and popABC) were characterized by deletion analysis, and the HrpB-dependent activation of these promoters was found to be conferred by a 25-nucleotide DNA element, the hrp(II) box (TTCGn16TTCG), which is present in other hrp promoters. The hrp(II) box element is an imperfect plant inducible promoter box, an element which was originally found in hrp promoters of Xanthomonas campestris (S. Fenselau and U. Bonas, Mol. Plant-Microbe Interact. 8:845-854, 1995) but which was not characterized at the molecular level. Site-directed mutagenesis showed that the hrp(II) box is essential for hrpY promoter activation in vivo. Functional analysis of the hrp(II) box element identified critical parameters that are required for HrpB-dependent activity. Further mapping analyses of several other hrpB-dependent promoters also indicated that the position of the hrp(II) box is conserved, at -70 to -47 bp from the transcriptional start. As a first step toward identifying novel TTSS effectors, we used the hrp(II) box consensus sequence to search for potential HrpB-regulated promoters in the complete genome sequence of R. solanacearum strain GMI1000. Among the 114 genes identified, a subset of promoters was found to have a structural relationship with hrp promoters, thus providing a pool of candidate genes encoding TTSS effectors.
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Affiliation(s)
- Sébastien Cunnac
- Laboratoire Interactions Plantes-Microorganismes, CNRS-INRA, UMR2594, BP27, 31326 Castanet-Tolosan, France
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106
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Furutani A, Tsuge S, Ohnishi K, Hikichi Y, Oku T, Tsuno K, Inoue Y, Ochiai H, Kaku H, Kubo Y. Evidence for HrpXo-dependent expression of type II secretory proteins in Xanthomonas oryzae pv. oryzae. J Bacteriol 2004; 186:1374-80. [PMID: 14973015 PMCID: PMC344398 DOI: 10.1128/jb.186.5.1374-1380.2004] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Xanthomonas oryzae pv. oryzae is a causal agent of bacterial leaf blight of rice. Recently, an efficient hrp-inducing medium, XOM2, was established for this bacterium. In this medium, more than 10 proteins were secreted from the wild-type strain of X. oryzae pv. oryzae. Many of these proteins disappeared or decreased in amount in culture on XOM2 when incubated with the strain that has a mutation in the hrp regulatory gene. Interestingly, the secretory protein profile of a mutant lacking a type III secretion system (TTSS), components of which are encoded by hrp genes, was similar to that of the wild-type strain except that a few proteins had disappeared. This finding suggests that many HrpXo-dependent secretory proteins are secreted via systems other than the TTSS. By isolating mutant strains lacking a type II secretion system, we examined this hypothesis. As expected, many of the HrpXo-dependent secretory proteins disappeared or decreased when the mutant was cultured in XOM2. By determining the N-terminal amino acid sequence, we identified one of the type II secretory proteins as a cysteine protease homolog, CysP2. Nucleotide sequence analysis revealed that cysP2 has an imperfect plant-inducible-promoter box, a consensus sequence which HrpXo regulons possess in the promoter region, and a deduced signal peptide sequence at the N terminus. By reverse transcription-PCR analysis and examination of the expression of CysP2 by using a plasmid harboring a cysP2::gus fusion gene, HrpXo-dependent expression of CysP2 was confirmed. Here, we reveal that the hrp regulatory gene hrpXo is also involved in the expression of not only hrp genes and type III secretory proteins but also some type II secretory proteins.
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Affiliation(s)
- Ayako Furutani
- Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto Prefectural University, Kyoto 606-8522, Japan
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107
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Noël L, Thieme F, Gäbler J, Büttner D, Bonas U. XopC and XopJ, two novel type III effector proteins from Xanthomonas campestris pv. vesicatoria. J Bacteriol 2004; 185:7092-102. [PMID: 14645268 PMCID: PMC296255 DOI: 10.1128/jb.185.24.7092-7102.2003] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pathogenicity of the gram-negative plant pathogen Xanthomonas campestris pv. vesicatoria depends on a type III secretion (TTS) system which translocates bacterial effector proteins into the plant cell. Previous transcriptome analysis identified a genome-wide regulon of putative virulence genes that are coexpressed with the TTS system. In this study, we characterized two of these genes, xopC and xopJ. Both genes encode Xanthomonas outer proteins (Xops) that were shown to be secreted by the TTS system. In addition, type III-dependent translocation of both proteins into the plant cell was demonstrated using the AvrBs3 effector domain as a reporter. XopJ belongs to the AvrRxv/YopJ family of effector proteins from plant and animal pathogenic bacteria. By contrast, XopC does not share significant homology to proteins in the database. Sequence analysis revealed that the xopC locus contains several features that are reminiscent of pathogenicity islands. Interestingly, the xopC region is flanked by 62-bp inverted repeats that are also associated with members of the Xanthomonas avrBs3 effector family. Besides xopC, a second gene of the locus, designated hpaJ, was shown to be coexpressed with the TTS system. hpaJ encodes a protein with similarity to transglycosylases and to the Pseudomonas syringae pv. maculicola protein HopPmaG. HpaJ secretion and translocation by the X. campestris pv. vesicatoria TTS system was not detectable, which is consistent with its predicted Sec signal and a putative function as transglycosylase in the bacterial periplasm.
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Affiliation(s)
- Laurent Noël
- Institute of Genetics, Martin-Luther-University Halle-Wittenberg, D-06099 Halle (Saale), Germany
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108
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Alfano JR, Collmer A. Type III secretion system effector proteins: double agents in bacterial disease and plant defense. ANNUAL REVIEW OF PHYTOPATHOLOGY 2004; 42:385-414. [PMID: 15283671 DOI: 10.1146/annurev.phyto.42.040103.110731] [Citation(s) in RCA: 507] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Many phytopathogenic bacteria inject virulence effector proteins into plant cells via a Hrp type III secretion system (TTSS). Without the TTSS, these pathogens cannot defeat basal defenses, grow in plants, produce disease lesions in hosts, or elicit the hypersensitive response (HR) in nonhosts. Pathogen genome projects employing bioinformatic methods to identify TTSS Hrp regulon promoters and TTSS pathway targeting signals suggest that phytopathogenic Pseudomonas, Xanthomonas, and Ralstonia spp. harbor large arsenals of effectors. The Hrp TTSS employs customized cytoplasmic chaperones, conserved export components in the bacterial envelope (also used by the TTSS of animal pathogens), and a more specialized set of TTSS-secreted proteins to deliver effectors across the plant cell wall and plasma membrane. Many effectors can act as molecular double agents that betray the pathogen to plant defenses in some interactions and suppress host defenses in others. Investigations of the functions of effectors within plant cells have demonstrated the plasma membrane and nucleus as subcellular sites for several effectors, revealed some effectors to possess cysteine protease or protein tyrosine phosphatase activity, and provided new clues to the coevolution of bacterium-plant interactions.
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Affiliation(s)
- James R Alfano
- The Plant Science Initiative and the Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska, 68588-0660, USA.
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109
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Marie C, Deakin WJ, Viprey V, Kopciñska J, Golinowski W, Krishnan HB, Perret X, Broughton WJ. Characterization of Nops, nodulation outer proteins, secreted via the type III secretion system of NGR234. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2003; 16:743-51. [PMID: 12971597 DOI: 10.1094/mpmi.2003.16.9.743] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The nitrogen-fixing symbiotic bacterium Rhizobium species NGR234 secretes, via a type III secretion system (TTSS), proteins called Nops (nodulation outer proteins). Abolition of TTSS-dependent protein secretion has either no effect or leads to a change in the number of nodules on selected plants. More dramatically, Nops impair nodule development on Crotalaria juncea roots, resulting in the formation of nonfixing pseudonodules. A double mutation of nopX and nopL, which code for two previously identified secreted proteins, leads to a phenotype on Pachyrhizus tuberosus differing from that of a mutant in which the TTSS is not functional. Use of antibodies and a modification of the purification protocol revealed that NGR234 secretes additional proteins in a TTSS-dependent manner. One of them was identified as NopA, a small 7-kDa protein. Single mutations in nopX and nopL were also generated to assess the involvement of each Nop in protein secretion and nodule formation. Mutation of nopX had little effect on NopL and NopA secretion but greatly affected the interaction of NGR234 with many plant hosts tested. NopL was not necessary for the secretion of any Nops but was required for efficient nodulation of some plant species. NopL may thus act as an effector protein whose recognition is dependent upon the hosts' genetic background.
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Affiliation(s)
- Corinne Marie
- Laboratoire de Biologie Moléculaire des Plantes Supérieures, University of Geneva, 1 chemin de l'Impératrice, CH1292 Chambésy-Geneva, Switzerland
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110
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Affiliation(s)
- Annick Gauthier
- Biotechnology Laboratory and Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
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111
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Kim JG, Park BK, Yoo CH, Jeon E, Oh J, Hwang I. Characterization of the Xanthomonas axonopodis pv. glycines Hrp pathogenicity island. J Bacteriol 2003; 185:3155-66. [PMID: 12730176 PMCID: PMC154065 DOI: 10.1128/jb.185.10.3155-3166.2003] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2002] [Accepted: 02/16/2003] [Indexed: 11/20/2022] Open
Abstract
We sequenced an approximately 29-kb region from Xanthomonas axonopodis pv. glycines that contained the Hrp type III secretion system, and we characterized the genes in this region by Tn3-gus mutagenesis and gene expression analyses. From the region, hrp (hypersensitive response and pathogenicity) and hrc (hrp and conserved) genes, which encode type III secretion systems, and hpa (hrp-associated) genes were identified. The characteristics of the region, such as the presence of many virulence genes, low G+C content, and bordering tRNA genes, satisfied the criteria for a pathogenicity island (PAI) in a bacterium. The PAI was composed of nine hrp, nine hrc, and eight hpa genes with seven plant-inducible promoter boxes. The hrp and hrc mutants failed to elicit hypersensitive responses in pepper plants but induced hypersensitive responses in all tomato plants tested. The Hrp PAI of X. axonopodis pv. glycines resembled the Hrp PAIs of other Xanthomonas species, and the Hrp PAI core region was highly conserved. However, in contrast to the PAI of Pseudomonas syringae, the regions upstream and downstream from the Hrp PAI core region showed variability in the xanthomonads. In addition, we demonstrate that HpaG, which is located in the Hrp PAI region of X. axonopodis pv. glycines, is a response elicitor. Purified HpaG elicited hypersensitive responses at a concentration of 1.0 micro M in pepper, tobacco, and Arabidopsis thaliana ecotype Cvi-0 by acting as a type III secreted effector protein. However, HpaG failed to elicit hypersensitive responses in tomato, Chinese cabbage, and A. thaliana ecotypes Col-0 and Ler. This is the first report to show that the harpin-like effector protein of Xanthomonas species exhibits elicitor activity.
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Affiliation(s)
- Jung-Gun Kim
- School of Agricultural Biotechnology, Seoul National University, Suwon 441-744, Korea
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112
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Shen Y, Ronald P. Molecular determinants of disease and resistance in interactions of Xanthomonas oryzae pv. oryzae and rice. Microbes Infect 2002; 4:1361-7. [PMID: 12443901 DOI: 10.1016/s1286-4579(02)00004-7] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Xanthomonas oryzae pv. oryzae is the causal agent of rice bacterial blight disease. Numerous genes critical for virulence have been identified. This article reviews current knowledge on the molecular mechanisms of X. oryzae pv. oryzae virulence.
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Affiliation(s)
- Yuwei Shen
- Department of Plant Pathology, University of California, Davis 95616, USA
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113
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Büttner D, Bonas U. Getting across--bacterial type III effector proteins on their way to the plant cell. EMBO J 2002; 21:5313-22. [PMID: 12374732 PMCID: PMC129068 DOI: 10.1093/emboj/cdf536] [Citation(s) in RCA: 183] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Pathogenicity of most Gram-negative bacterial plant pathogens depends on hrp (hypersensitive response and pathogenicity) genes, which control the ability to cause disease and to elicit specific defense responses in resistant plants. hrp genes encode a specialized type III secretion (TTS) system that mediates the vectorial delivery of bacterial effector proteins across both bacterial membranes as well as across the eukaryotic plasma membrane into the host cell cytosol. One well-studied effector protein is AvrBs3 from Xanthomonas campestris pv. vesicatoria, the causal agent of bacterial spot in pepper and tomato. AvrBs3 induces hypertrophy symptoms in susceptible plants and triggers a resistance gene-specific cell death reaction in resistant plants. Intriguingly, AvrBs3 has characteristic features of eukaryotic transcription factors, suggesting that it modulates the host's transcriptome. Here, we discuss the TTS system of X.campestris pv. vesicatoria in the light of current knowledge on type III-dependent protein secretion in plant pathogenic bacteria.
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Affiliation(s)
- Daniela Büttner
- Institut für Genetik, Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle (Saale), Germany.
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114
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Szurek B, Rossier O, Hause G, Bonas U. Type III-dependent translocation of the Xanthomonas AvrBs3 protein into the plant cell. Mol Microbiol 2002; 46:13-23. [PMID: 12366827 DOI: 10.1046/j.1365-2958.2002.03139.x] [Citation(s) in RCA: 132] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Many plant pathogenic bacteria utilize a conserved type III secretion system (TTSS) to deliver effector proteins into the host tissue. Indirect evidence has suggested that at least some effector proteins are translocated from the bacterial cytoplasm into the plant cell. Using an immunocytochemical approach, we demonstrate that the type III effector AvrBs3 from Xanthomonas campestris pv. vesicatoria localizes to nuclei of infected pepper leaves. Importantly, AvrBs3 translocation was observed in situ in native tissues of susceptible and resistant plants. AvrBs3 was detected in the nucleus as soon as 4 h post infection, which was dependent on a functional TTSS and the putative translocator HrpF. N-terminal AvrBs3 deletion derivatives are no longer secreted by the TTSS in vitro and could not be detected inside the host cells, suggesting that the N-terminus of AvrBs3 is important for secretion. Deletion of the nuclear localization signals in the AvrBs3 C-terminus, which are required for the AvrBs3-mediated induction of the hypersensitive reaction in resistant pepper plants, abolished AvrBs3 localization to the nucleus. This is the first report on direct evidence for translocation of a native type III effector protein from a plant pathogenic bacterium into the host cell.
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Affiliation(s)
- Boris Szurek
- Institut für Genetik, Martin-Luther-Universität Halle-Wittenberg, Halle, Germany
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115
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Collmer A, Lindeberg M, Petnicki-Ocwieja T, Schneider DJ, Alfano JR. Genomic mining type III secretion system effectors in Pseudomonas syringae yields new picks for all TTSS prospectors. Trends Microbiol 2002; 10:462-9. [PMID: 12377556 DOI: 10.1016/s0966-842x(02)02451-4] [Citation(s) in RCA: 194] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Many bacterial pathogens of plants and animals use a type III secretion system (TTSS) to deliver virulence effector proteins into host cells. Because effectors are heterogeneous in sequence and function, there has not been a systematic way to identify the genes encoding them in pathogen genomes, and our current inventories are probably incomplete. A pre-closure draft sequence of Pseudomonas syringae pv. tomato DC3000, a pathogen of tomato and Arabidopsis, has recently supported five complementary studies which, collectively, identify 36 TTSS-secreted proteins and many more candidate effectors in this strain. These studies demonstrate the advantages of combining experimental and computational approaches, and they yield new insights into TTSS effectors and virulence regulation in P. syringae, potential effector targeting signals in all TTSS-dependent pathogens, and strategies for finding TTSS effectors in other bacteria that have sequenced genomes.
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Affiliation(s)
- Alan Collmer
- Dept of Plant Pathology, Cornell University, Ithaca, NY 14850-4203, USA
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116
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Abstract
Many Gram-negative plant and animal pathogenic bacteria use a specialized type III secretion system (TTSS) as a molecular syringe to inject effector proteins directly into the host cell. Protein translocation across the eukaryotic host cell membrane is presumably mediated by a bacterial translocon. The structure of this predicted transmembrane complex and the mechanism of transport are far from being understood. In bacterial pathogens of animals, several putative type III secretion translocon proteins (TTPs) have been identified. Interestingly, TTP sequences are not conserved among different bacterial species, however, there are structural similarities such as transmembrane segments and coiled-coil regions. Accumulating evidence suggests that TTPs are components of oligomeric protein channels that are inserted into the host cell membrane by the TTSS.
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Affiliation(s)
- Daniela Büttner
- Institut für Genetik, Martin-Luther-Universität Halle-Wittenberg, D-06099 (Saale), Halle, Germany.
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