scholarly journals PrhN, a putative marR family transcriptional regulator, is involved in positive regulation of type III secretion system and full virulence of Ralstonia solanacearum

2015 ◽  
Vol 6 ◽  
Author(s):  
Yong Zhang ◽  
Feng Luo ◽  
Dousheng Wu ◽  
Yasufumi Hikichi ◽  
Akinori Kiba ◽  
...  
Keyword(s):  
Ralstonia Solanacearum ◽  
Type Iii Secretion ◽  
Type Iii Secretion System ◽  
Transcriptional Regulator ◽  
Secretion System ◽  
Positive Regulation ◽  
Type Iii

scholarly journals PrhG, a Transcriptional Regulator Responding to Growth Conditions, Is Involved in the Control of the Type III Secretion System Regulon in Ralstonia solanacearum

2009 ◽  
Vol 192 (4) ◽  
pp. 1011-1019 ◽  
Author(s):  
Laure Plener ◽  
Pablo Manfredi ◽  
Marc Valls ◽  
Stéphane Genin
Keyword(s):  
Ralstonia Solanacearum ◽  
Type Iii Secretion ◽  
Minimal Medium ◽  
Type Iii Secretion System ◽  
Transcriptional Regulator ◽  
Secretion System ◽  
Host Cells ◽  
Bacterial Disease ◽  
Type Iii ◽  
Regulatory Cascade

ABSTRACT The ability of Ralstonia solanacearum to cause disease in plants depends on its type III secretion system (T3SS). The expression of the T3SS and its effector substrates is coordinately controlled by a regulatory cascade, at the bottom of which is HrpB. Transcription of the hrpB gene is activated by a plant-responsive regulator named HrpG, which is a master regulator of a wide array of pathogenicity functions in R. solanacearum. We have identified in the genome of strain GMI1000 a close paralog of hrpG (83% overall similarity at the protein level) that we have named prhG. Despite this high similarity, the expression pattern of prhG is remarkably different from that of hrpG: prhG expression is activated after growth of bacteria in minimal medium but not in the presence of host cells, while hrpG expression is specifically induced in response to plant cell signals. We provide genetic evidence that prhG is a transcriptional regulator that, like hrpG, controls the expression of hrpB and the hrpB-regulated genes under minimal medium conditions. However, the regulatory functions of prhG and hrpG are distinct: prhG has no influence on hrpB expression when the bacteria are in the presence of plant cells, and transcriptomic profiling analysis of a prhG mutant revealed that the PrhG and HrpG regulons have only one pathogenicity target in common, hrpB. Functional complementation experiments indicated that PrhG and HrpG are individually sufficient to activate hrpB expression in minimal medium. Rather surprisingly, a prhG disruption mutant had little impact on pathogenicity, which may indicate that prhG has a minor role in the activation of T3SS genes when R. solanacearum grows parasitically inside the plant. The cross talk between pathogenicity regulatory proteins and environmental signals described here denotes that an intricate network is at the basis of the bacterial disease program.

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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