scholarly journals Integrated Regulation of the Type III Secretion System and Other Virulence Determinants in Ralstonia solanacearum

2006 ◽  
Vol 2 (8) ◽  
pp. e82 ◽  
Author(s):  
Marc Valls ◽  
Stéphane Genin ◽  
Christian Boucher
Keyword(s):  
Ralstonia Solanacearum ◽  
Type Iii Secretion ◽  
Type Iii Secretion System ◽  
Secretion System ◽  
Virulence Determinants ◽  
Type Iii ◽  
Integrated Regulation

scholarly journals A Type III Secretion System Is Required for Aeromonas hydrophila AH-1 Pathogenesis

2004 ◽  
Vol 72 (3) ◽  
pp. 1248-1256 ◽  
Author(s):  
H. B. Yu ◽  
P. S. Srinivasa Rao ◽  
H. C. Lee ◽  
S. Vilches ◽  
S. Merino ◽  
...  
Keyword(s):  
Aeromonas Hydrophila ◽  
Type Iii Secretion ◽  
Type Iii Secretion System ◽  
Gene Clusters ◽  
Opportunistic Pathogen ◽  
Secretion System ◽  
Virulence Determinants ◽  
Degenerate Primers ◽  
Type Iii ◽  
Insertional Inactivation

ABSTRACT Aeromonas hydrophila is a gram-negative opportunistic pathogen in fish and humans. Many bacterial pathogens of animals and plants have been shown to inject anti-host virulence determinants into the hosts via a type III secretion system (TTSS). Degenerate primers based on lcrD family genes that are present in every known TTSS allowed us to locate the TTSS gene cluster in A. hydrophila AH-1. A series of genome walking steps helped in the identification of 25 open reading frames that encode proteins homologous to those in TTSSs in other bacteria. PCR-based analysis showed the presence of lcrD homologs (ascV) in all of the 33 strains of A. hydrophila isolated from various sources. Insertional inactivation of two of the TTSS genes (aopB and aopD) led to decreased cytotoxicity in carp epithelial cells, increased phagocytosis, and reduced virulence in blue gourami. These results show that a TTSS is required for A. hydrophila pathogenesis. This is the first report of sequencing and characterization of TTSS gene clusters from A. hydrophila. The TTSS identified here may help in developing suitable vaccines as well as in further understanding of the pathogenesis of A. hydrophila.

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

2010 ◽  
Vol 23 (5) ◽  
pp. 665-681 ◽  
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.

scholarly journals Two Type III Secretion System Effectors from Ralstonia solanacearum GMI1000 Determine Host-Range Specificity on Tobacco

2009 ◽  
Vol 22 (5) ◽  
pp. 538-550 ◽  
Author(s):  
Marie Poueymiro ◽  
Sébastien Cunnac ◽  
Patrick Barberis ◽  
Laurent Deslandes ◽  
Nemo Peeters ◽  
...  
Keyword(s):  
Host Range ◽  
Ralstonia Solanacearum ◽  
Type Iii Secretion ◽  
Tandem Repeats ◽  
Hypervariable Region ◽  
Type Iii Secretion System ◽  
Defense Responses ◽  
Secretion System ◽  
Tobacco Plants ◽  
Type Iii

The model pathogen Ralstonia solanacearum GMI1000 is the causal agent of the bacterial wilt disease that attacks many solanaceous plants and other hosts but not tobacco (Nicotiana spp.). We found that two type III secretion system effector genes, avrA and popP1, are limiting the host range of strain GMI1000 on at least three tobacco species (N. tabacum, N. benthamiana, and N. glutinosa). Both effectors elicit the hypersensitive response (HR) on these tobacco species, although in different manners; AvrA is the major determinant recognized by N. tabacum and N. benthamiana, while PopP1 appears to be the major HR elicitor on N. glutinosa. Only the double inactivation of the avrA and popP1 genes allowed GMI1000 to wilt tobacco plants, thus showing that GMI1000 intrinsically possesses the functions necessary to wilt tobacco plants. A focused analysis on AvrA revealed that the first 58 N-terminal amino acids are sufficient to direct its injection into plant cells. We identified a hypervariable region in avrA, which contains variable numbers of tandem repeats (VNTR), each composed of 12 base pairs. We show that an 18–amino acid region in which the VNTR insertion occurs is an important domain involved in HR elicitation on N. benthamiana. avrA appears to be the target of various DNA insertions or mobile elements that probably allow R. solanacearum to evade the recognition and defense responses of tobacco.

scholarly journals Characterization of the cis-Acting Regulatory Element Controlling HrpB-Mediated Activation of the Type III Secretion System and Effector Genes in Ralstonia solanacearum

2004 ◽  
Vol 186 (8) ◽  
pp. 2309-2318 ◽  
Author(s):  
Sébastien Cunnac ◽  
Christian Boucher ◽  
Stéphane Genin
Keyword(s):  
Ralstonia Solanacearum ◽  
Type Iii Secretion ◽  
Xanthomonas Campestris ◽  
Consensus Sequence ◽  
Type Iii Secretion System ◽  
Secretion System ◽  
Site Directed Mutagenesis ◽  
Critical Parameters ◽  
Type Iii ◽  
Regulated Promoters

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.

scholarly journals Functional Characterization of RsRsgA for Ribosome Biosynthesis and Expression of the Type III Secretion System in Ralstonia solanacearum

2020 ◽  
Vol 33 (7) ◽  
pp. 972-981
Author(s):  
Jiaman Li ◽  
Liangliang Han ◽  
Nan Chen ◽  
Chao Zhu ◽  
Yuwei Gao ◽  
...  
Keyword(s):  
Ralstonia Solanacearum ◽  
Type Iii Secretion ◽  
Functional Characterization ◽  
Type Iii Secretion System ◽  
Secretion System ◽  
In Planta ◽  
Tobacco Leaves ◽  
Type Iii ◽  
30S Subunit ◽  
Ribosome Biosynthesis

RsgA plays an important role in maturation of 30S subunit in many bacteria that assists in the release of RbfA from the 30S subunit during a late stage of ribosome biosynthesis. Here, we genetically characterized functional roles of RsgA in Ralstonia solanacearum, hereafter designated RsRsgA. Deletion of R. solanacearum rsgA or rbfA resulted in distinct deficiency of 16S ribosomal RNA, significantly slowed growth in broth medium, and diminished growth in nutrient-limited medium, which are similar as phenotypes of rsgA mutants and rbfA mutants of Escherichia coli and other bacteria. Our gene-expression studies revealed that RsRsgA is important for expression of genes encoding the type III secretion system (T3SS) (a pathogenicity determinant of R. solanacearum) both in vitro and in planta. Compared with the wild-type R. solanacearum strain, proliferation of the rsgA and rbfA mutants in tobacco leaves was significantly impaired, while they failed to migrate into tobacco xylem vessels from infiltrated leaves, and hence, these two mutants failed to cause any bacterial wilt disease in tobacco plants. It was further revealed that rsgA expression was highly enhanced under nutrient-limited conditions compared with that in broth medium and RsRsgA affects T3SS expression through the PrhN-PrhG-HrpB pathway. Moreover, expression of a subset of type III effectors was substantially impaired in the rsgA mutant, some of which are responsible for R. solanacearum GMI1000 elicitation of a hypersensitive response (HR) in tobacco leaves, while RsRsgA is not required for HR elicitation of GMI1000 in tobacco leaves. All these results provide novel insights into understanding various biological functions of RsgA proteins and complex regulation on the T3SS in R. solanacearum.

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