Department of Medical Laboratory Science and Biotechnology, Central Taiwan University of Science and Technology, Taichung 406, Taiwan, ROC.
Res Microbiol. 2011 Apr;162(3):270-8. doi: 10.1016/j.resmic.2010.12.002. Epub 2010 Dec 25.
Exopolysaccharides and several extracellular enzymes of Xanthomonas campestris pv. campestris (Xcc), the causative agent of black rot in crucifers, are virulence determinants. It is known that Clp (cAMP receptor protein-like protein) and RpfF (an enoyl-CoA hydratase homologue required for the synthesis of the diffusible signal factor, DSF) regulate production of these factors. In this study, plate assay revealed that Xcc possesses pectin methylesterase activity and that its expression is controlled by Clp and RpfF. Mutational analysis has demonstrated that pmeA encodes a pectin methylesterase. Using the 5' RACE method, the pmeA transcription initiation site was mapped. Transcriptional fusion assays showed that pmeA transcription is positively regulated by Clp and RpfF, subject to catabolite repression which is independent of Clp or RpfF, and repressed under conditions of high osmolarity or oxygen limitation. This study not only extends previous work on Clp and RpfF regulation by showing that they both influence the expression of pmeA in Xcc, but also, for the first time, characterizes pectin methylesterase gene expression in Xanthomonas.
黄单胞菌属野油菜致病变种（Xcc）是十字花科黑腐病的病原体，其胞外多糖和几种胞外酶是致病因子。已知 Clp（cAMP 受体蛋白样蛋白）和 RpfF（一种烯酰辅酶 A 水合酶同源物，对于扩散信号因子 DSF 的合成是必需的）调节这些因子的产生。在这项研究中，平板测定表明 Xcc 具有果胶甲酯酶活性，其表达受 Clp 和 RpfF 控制。突变分析表明 pmeA 编码果胶甲酯酶。使用 5' RACE 方法，定位了 pmeA 的转录起始位点。转录融合分析表明，pmeA 的转录受 Clp 和 RpfF 的正调控，受分解代谢物阻遏的影响，该阻遏作用不依赖于 Clp 或 RpfF，并且在高渗透压或氧气限制条件下受到抑制。这项研究不仅通过表明它们都影响 Xcc 中 pmeA 的表达，扩展了之前关于 Clp 和 RpfF 调控的工作，而且首次表征了黄单胞菌中果胶甲酯酶基因的表达。
