Hypersensitive response suppression by type III effectors of plant pathogenic bacteria

ABSTRACT Pseudomonas syringae utilizes the type III secretion system to translocate effector proteins into plant cells, where they can contribute to the pathogen's ability to infect and cause disease. Recognition of these effectors by resistance proteins induces defense responses that typically include a programmed cell death reaction called the hypersensitive response. The YopJ/HopZ family of type III effector proteins is a common family of effector proteins found in animal- and plant-pathogenic bacteria. The HopZ family in P. syringae includes HopZ1aPsyA2, HopZ1bPgyUnB647, HopZ1cPmaE54326, HopZ2Ppi895A and HopZ3PsyB728a. HopZ1a is predicted to be most similar to the ancestral hopZ allele and causes a hypersensitive response in multiple plant species, including Arabidopsis thaliana. Therefore, it has been proposed that host defense responses have driven the diversification of this effector family. In this study, we further characterized the hypersensitive response induced by HopZ1a and demonstrated that it is not dependent on known resistance genes. Further, we identified a novel virulence function for HopZ2 that requires the catalytic cysteine demonstrated to be required for protease activity. Sequence analysis of the HopZ family revealed the presence of a predicted myristoylation sequence in all members except HopZ3. We demonstrated that the myristoylation site is required for membrane localization of this effector family and contributes to the virulence and avirulence activities of HopZ2 and HopZ1a, respectively. This paper provides insight into the selective pressures driving virulence protein evolution by describing a detailed functional characterization of the diverse HopZ family of type III effectors with the model plant Arabidopsis.

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Regulation of the Type III Secretion System in Phytopathogenic Bacteria

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-19-1159 ◽

2006 ◽

Vol 19 (11) ◽

pp. 1159-1166 ◽

Cited By ~ 134

Author(s):

Xiaoyan Tang ◽

Yanmei Xiao ◽

Jian-Min Zhou

Keyword(s):

Signal Transduction ◽

Hypersensitive Response ◽

Type Iii Secretion ◽

Pathogenic Bacteria ◽

Type Iii Secretion System ◽

Secretion System ◽

Host Cells ◽

Plant Pathogenic Bacteria ◽

Type Iii ◽

Hrp Genes

The type III secretion system (TTSS) is a specialized protein secretion machinery used by numerous gram-negative bacterial pathogens of animals and plants to deliver effector proteins directly into the host cells. In plant-pathogenic bacteria, genes encoding the TTSS were discovered as hypersensitive response and pathogenicity (hrp) genes, because mutation of these genes typically disrupts the bacterial ability to cause diseases on host plants and to elicit hypersensitive response on nonhost plants. The hrp genes and the type III effector genes (collectively called TTSS genes hereafter) are repressed in nutrient-rich media but induced when bacteria are infiltrated into plants or incubated in nutrient-deficient inducing media. Multiple regulatory components have been identified in the plant-pathogenic bacteria regulating TTSS genes under various conditions. In Ralstonia solanacearum, several signal transduction components essential for the induction of TTSS genes in plants are dispensable for the induction in inducing medium. In addition to the inducing signals, recent studies indicated the presence of negative signals in the plant regulating the Pseudomonas syringae TTSS genes. Thus, the levels of TTSS gene expression in plants likely are determined by the interactions of multiple signal transduction pathways. Studies of the hrp regulons indicated that TTSS genes are coordinately regulated with a number of non-TTSS genes.

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Amyloidogenesis of Type III-dependent Harpins from Plant Pathogenic Bacteria

Journal of Biological Chemistry ◽

10.1074/jbc.m602576200 ◽

2007 ◽

Vol 282 (18) ◽

pp. 13601-13609 ◽

Cited By ~ 68

Author(s):

Jonghee Oh ◽

Jung-Gun Kim ◽

Eunkyung Jeon ◽

Chang-Hyuk Yoo ◽

Jae Sun Moon ◽

...

Keyword(s):

Pathogenic Bacteria ◽

Plant Pathogenic Bacteria ◽

Type Iii

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Identification of Novel Type III Secretion Effectors in Xanthomonas oryzae pv. oryzae

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-22-1-0096 ◽

2009 ◽

Vol 22 (1) ◽

pp. 96-106 ◽

Cited By ~ 71

Author(s):

Ayako Furutani ◽

Minako Takaoka ◽

Harumi Sanada ◽

Yukari Noguchi ◽

Takashi Oku ◽

...

Keyword(s):

Pseudomonas Syringae ◽

Type Iii Secretion ◽

Pathogenic Bacteria ◽

Regulatory Protein ◽

Effector Proteins ◽

Xanthomonas Oryzae ◽

Dependent Manner ◽

Plant Pathogenic Bacteria ◽

Type Iii ◽

Genes Encoding

Many gram-negative bacteria secrete so-called effector proteins via a type III secretion (T3S) system. Through genome screening for genes encoding potential T3S effectors, 60 candidates were selected from rice pathogen Xanthomonas oryzae pv. oryzae MAFF311018 using these criteria: i) homologs of known T3S effectors in plant-pathogenic bacteria, ii) genes with expression regulated by hrp regulatory protein HrpX, or iii) proteins with N-terminal amino acid patterns associated with T3S substrates of Pseudomonas syringae. Of effector candidates tested with the Bordetella pertussis calmodulin-dependent adenylate cyclase reporter for translocation into plant cells, 16 proteins were translocated in a T3S system-dependent manner. Of these 16 proteins, nine were homologs of known effectors in other plant-pathogenic bacteria and seven were not. Most of the effectors were widely conserved in Xanthomonas spp.; however, some were specific to X. oryzae. Interestingly, all these effectors were expressed in an HrpX-dependent manner, suggesting coregulation of effectors and the T3S system. In X. campestris pv. vesicatoria, HpaB and HpaC (HpaP in X. oryzae pv. oryzae) have a central role in recruiting T3S substrates to the secretion apparatus. Secretion of all but one effector was reduced in both HpaB– and HpaP– mutant strains, indicating that HpaB and HpaP are widely involved in efficient secretion of the effectors.

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Positive Regulation of the Hrp Type III Secretion System in Pseudomonas syringae pv. phaseolicola

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-23-5-0665 ◽

2010 ◽

Vol 23 (5) ◽

pp. 665-681 ◽

Cited By ~ 40

Author(s):

Inmaculada Ortiz-Martín ◽

Richard Thwaites ◽

Alberto P. Macho ◽

John W. Mansfield ◽

Carmen R. Beuzón

Keyword(s):

Gene Expression ◽

Pseudomonas Syringae ◽

Hypersensitive Response ◽

Type Iii Secretion ◽

Pathogenic Bacteria ◽

Type Iii Secretion System ◽

Secretion System ◽

Virulence Determinants ◽

Type Iii

Disease in compatible hosts and induction of the hypersensitive response in resistant plants by most plant-pathogenic bacteria require a functional type III secretion system (T3SS). Expression of T3SS genes responds to host and environmental factors and is induced within the plant. In Pseudomonas syringae, expression of the T3SS requires HrpL, which is transcriptionally upregulated by HrpR and HrpS. In some pathovars, expression of the hrpRS genes is upregulated by the GacA/S two-component system. Additionally, HrpA, the major component of the T3SS pilus, has also been linked to the regulation of the hrpRS gene expression. Previous studies concerning regulation of hypersensitive response and pathogenesis/hypersensitive response conserved (hrp/hrc) gene expression have used mostly in vitro inducing conditions, different pathovars, and methodology. Here, we analyze the roles of HrpL, GacA, and HrpA in the bean pathogen, using single, double, and triple mutants as well as strains ectopically expressing the regulators. We use real-time polymerase chain reaction analysis in vitro and in planta to quantify gene expression and competitive indices and other assays to assess bacterial fitness. Our results indicate that i) HrpL acts as a general virulence regulator that upregulates non-T3SS virulence determinants and downregulates flagellar function; ii) GacA modulates the expression of hrpL, and its contribution to virulence is entirely HrpL dependent; iii) there is a basal HrpL-independent expression of the T3SS genes in rich medium that is important for full activation of the system, maybe by keeping the system primed for rapid activation upon contact with the plant; and iv) HrpA upregulates expression of the T3SS genes and is essential to activate expression of the hrpZ operon upon contact with the plant.

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The Type III Secretion System of Xanthomonas fuscans subsp. fuscans Is Involved in the Phyllosphere Colonization Process and in Transmission to Seeds of Susceptible Beans

Applied and Environmental Microbiology ◽

10.1128/aem.02906-07 ◽

2008 ◽

Vol 74 (9) ◽

pp. 2669-2678 ◽

Cited By ~ 42

Author(s):

A. Darsonval ◽

A. Darrasse ◽

D. Meyer ◽

M. Demarty ◽

K. Durand ◽

...

Keyword(s):

Type Iii Secretion ◽

Xanthomonas Campestris ◽

Pathogenic Bacteria ◽

Type Iii Secretion System ◽

Secretion System ◽

Regulatory Genes ◽

Population Densities ◽

Host Colonization ◽

Plant Pathogenic Bacteria ◽

Type Iii

ABSTRACT Understanding the survival, multiplication, and transmission to seeds of plant pathogenic bacteria is central to study their pathogenesis. We hypothesized that the type III secretion system (T3SS), encoded by hrp genes, could have a role in host colonization by plant pathogenic bacteria. The seed-borne pathogen Xanthomonas fuscans subsp. fuscans causes common bacterial blight of bean (Phaseolus vulgaris). Directed mutagenesis in strain CFBP4834-R of X. fuscans subsp. fuscans and bacterial population density monitoring on bean leaves showed that strains with mutations in the hrp regulatory genes, hrpG and hrpX, were impaired in their phyllospheric growth, as in the null interaction with Escherichia coli C600 and bean. In the compatible interaction, CFBP4834-R reached high phyllospheric population densities and was transmitted to seeds at high frequencies with high densities. Strains with mutations in structural hrp genes maintained the same constant epiphytic population densities (1 × 105 CFU g−1 of fresh weight) as in the incompatible interaction with Xanthomonas campestris pv. campestris ATCC 33913 and the bean. Low frequencies of transmission to seeds and low bacterial concentrations were recorded for CFBP4834-R hrp mutants and for ATCC 33913, whereas E. coli C600 was not transmitted. Moreover, unlike the wild-type strain, strains with mutations in hrp genes were not transmitted to seeds by vascular pathway. Transmission to seeds by floral structures remained possible for both. This study revealed the involvement of the X. fuscans subsp. fuscans T3SS in phyllospheric multiplication and systemic colonization of bean, leading to transmission to seeds. Our findings suggest a major contribution of hrp regulatory genes in host colonization processes.

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Multiple Activities of the Plant Pathogen Type III Effector Proteins WtsE and AvrE Require WxxxE Motifs

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-22-6-0703 ◽

2009 ◽

Vol 22 (6) ◽

pp. 703-712 ◽

Cited By ~ 32

Author(s):

Jong Hyun Ham ◽

Doris R. Majerczak ◽

Kinya Nomura ◽

Christy Mecey ◽

Francisco Uribe ◽

...

Keyword(s):

G Proteins ◽

Pseudomonas Syringae ◽

Virulence Factors ◽

Pathogenic Bacteria ◽

Plant Pathogens ◽

Biological Activities ◽

Defense Responses ◽

Endoplasmic Reticulum Membrane ◽

Type Iii Effectors ◽

Type Iii

The broadly conserved AvrE-family of type III effectors from gram-negative plant-pathogenic bacteria includes important virulence factors, yet little is known about the mechanisms by which these effectors function inside plant cells to promote disease. We have identified two conserved motifs in AvrE-family effectors: a WxxxE motif and a putative C-terminal endoplasmic reticulum membrane retention/retrieval signal (ERMRS). The WxxxE and ERMRS motifs are both required for the virulence activities of WtsE and AvrE, which are major virulence factors of the corn pathogen Pantoea stewartii subsp. stewartii and the tomato or Arabidopsis pathogen Pseudomonas syringae pv. tomato, respectively. The WxxxE and the predicted ERMRS motifs are also required for other biological activities of WtsE, including elicitation of the hypersensitive response in nonhost plants and suppression of defense responses in Arabidopsis. A family of type III effectors from mammalian bacterial pathogens requires WxxxE and subcellular targeting motifs for virulence functions that involve their ability to mimic activated G-proteins. The conservation of related motifs and their necessity for the function of type III effectors from plant pathogens indicates that disturbing host pathways by mimicking activated host G-proteins may be a virulence mechanism employed by plant pathogens as well.

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The Bradyrhizobium diazoefficiens type III effector NopE modulates the regulation of plant hormones towards nodulation in Vigna radiata

Scientific Reports ◽

10.1038/s41598-021-95925-4 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Pongdet Piromyou ◽

Hien P. Nguyen ◽

Pongpan Songwattana ◽

Pakpoom Boonchuen ◽

Kamonluck Teamtisong ◽

...

Keyword(s):

Salicylic Acid ◽

Plant Hormones ◽

Vigna Radiata ◽

Pathogenic Bacteria ◽

Evolutionary Analysis ◽

Host Genotype ◽

Type Iii Effectors ◽

Type Iii ◽

Calcium Dependent ◽

Symbiotic Interactions

AbstractHost-specific legume-rhizobium symbiosis is strictly controlled by rhizobial type III effectors (T3Es) in some cases. Here, we demonstrated that the symbiosis of Vigna radiata (mung bean) with Bradyrhizobium diazoefficiens USDA110 is determined by NopE, and this symbiosis is highly dependent on host genotype. NopE specifically triggered incompatibility with V. radiata cv. KPS2, but it promoted nodulation in other varieties of V. radiata, including KPS1. Interestingly, NopE1 and its paralogue NopE2, which exhibits calcium-dependent autocleavage, yield similar results in modulating KPS1 nodulation. Furthermore, NopE is required for early infection and nodule organogenesis in compatible plants. Evolutionary analysis revealed that NopE is highly conserved among bradyrhizobia and plant-associated endophytic and pathogenic bacteria. Our findings suggest that V. radiata and B. diazoefficiens USDA110 may use NopE to optimize their symbiotic interactions by reducing phytohormone-mediated ETI-type (PmETI) responses via salicylic acid (SA) biosynthesis suppression.

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