Institut für Biologie, Bereich Genetik, Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle (Saale), Germany.
New Phytol. 2010 Sep;187(4):983-1002. doi: 10.1111/j.1469-8137.2010.03312.x. Epub 2010 Jun 2.
*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.
许多植物病原菌的 II 型分泌（T2S）系统经常将细胞壁降解酶分泌到植物质外体中。在这里，我们表明，来自植物病原菌黄单胞菌 pv 斑疹亚种（Xcv）的 Xps-T2S 系统促进疾病并有助于效应蛋白的易位，这些效应蛋白通过 III 型分泌（T3S）系统递送到植物细胞中。相反，Xcs-T2S 系统缺乏明显的毒力功能。然而，单个 xcs 基因可以部分补充同源 xps 基因的突变体，表明它们编码 T2S 系统的功能组件。酶活性测定表明，Xps 系统有助于蛋白酶和木聚糖酶的分泌。我们确定了与毒力相关的木聚糖酶 XynC 是 Xps 系统的底物。然而，来自其他黄单胞菌属的已知 T2S 底物的同源物不能被 Xcv 的 T2S 系统分泌。因此，来自黄单胞菌属的 T2S 系统在底物特异性方面似乎有很大差异。转录分析显示，Xcv 中 xps 基因的表达被 T3S 系统的关键调节因子 HrpG 和 HrpX 激活。相比之下，xynC 和细胞外蛋白酶和木聚糖酶活性的表达受到 HrpG 和 HrpX 的抑制，表明 Xps 系统的组件和底物受到差异调节。
