Functional characterization of the Xcs and Xps type II secretion systems from the plant pathogenic bacterium Xanthomonas campestris pv vesicatoria.
*Type II secretion (T2S) systems of many plant-pathogenic bacteria often secrete cell wall-degrading enzymes into the plant apoplast. *Here, we show that the Xps-T2S system from the plant pathogen Xanthomonas campestris pv vesicatoria (Xcv) promotes disease and contributes to the translocation of effector proteins that are delivered into the plant cell by the type III secretion (T3S) system. *The Xcs-T2S system instead lacks an obvious virulence function. However, individual xcs genes can partially complement mutants in homologous xps genes, indicating that they encode functional components of T2S systems. Enzyme activity assays showed that the Xps system contributes to secretion of proteases and xylanases. We identified the virulence-associated xylanase XynC as a substrate of the Xps system. However, homologs of known T2S substrates from other Xanthomonas spp. are not secreted by the T2S systems from Xcv. Thus, T2S systems from Xanthomonas spp. appear to differ significantly in their substrate specificities. *Transcript analyses revealed that expression of xps genes in Xcv is activated by HrpG and HrpX, key regulators of the T3S system. By contrast, expression of xynC and extracellular protease and xylanase activities are repressed by HrpG and HrpX, suggesting that components and substrates of the Xps system are differentially regulated.
Robert
R
Szczesny
Matthias
M
Jordan
Institut für Biologie, Bereich Genetik, Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle (Saale), Germany.
Claudia
C
Schramm
Institut für Biologie, Bereich Genetik, Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle (Saale), Germany.
Steve
S
Schulz
Institut für Biologie, Bereich Genetik, Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle (Saale), Germany.
Virginie
V
Cogez
Institut für Biologie, Bereich Genetik, Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle (Saale), Germany.
Ulla
U
Bonas
Institut für Biologie, Bereich Genetik, Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle (Saale), Germany.
Daniela
D
Büttner
D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002212:Capsicum / Q000382:microbiology*; D043364:Endo-1,4-beta Xylanases / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D054884:Host-Pathogen Interactions / Q000235:genetics*; D010447:Peptide Hydrolases / Q000378:metabolism; D010935:Plant Diseases / Q000382:microbiology*; D013379:Substrate Specificity; D014157:Transcription Factors / Q000378:metabolism; D016959:Xanthomonas campestris / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*
D001426:Bacterial Proteins; C102404:HrpG protein, Xanthomonas campestris; D014157:Transcription Factors; D043364:Endo-1,4-beta Xylanases; D010447:Peptide Hydrolases