Department of Cell & Systems Biology, University of Toronto, Toronto, ON M5S 3B2, Canada.
Mol Microbiol. 2011 Apr;80(2):364-77. doi: 10.1111/j.1365-2958.2011.07571.x. Epub 2011 Feb 28.
Gram-negative bacterial pathogens have evolved a number of virulence-promoting strategies including the production of extracellular polysaccharides such as alginate and the injection of effector proteins into host cells. The induction of these virulence mechanisms can be associated with concomitant downregulation of the abundance of proteins that trigger the host immune system, such as bacterial flagellin. In Pseudomonas syringae, we observed that bacterial motility and the abundance of flagellin were significantly reduced under conditions that induce the type III secretion system. To identify genes involved in this negative regulation, we conducted a forward genetic screen with P. syringae pv. maculicola ES4326 using motility as a screening phenotype. We identified the periplasmic protease AlgW as a key negative regulator of flagellin abundance that also positively regulates alginate biosynthesis and the type III secretion system. We also demonstrate that AlgW constitutes a major virulence determinant of P. syringae required to dampen plant immune responses. Our findings support the conclusion that P. syringae co-ordinately regulates virulence strategies through AlgW in order to effectively suppress host immunity.
革兰氏阴性细菌病原体已经进化出许多促进毒力的策略，包括产生胞外多糖（如藻酸盐）和向宿主细胞注射效应蛋白。这些毒力机制的诱导可能伴随着触发宿主免疫系统的蛋白质丰度的下调，例如细菌鞭毛蛋白。在丁香假单胞菌中，我们观察到在诱导 III 型分泌系统的条件下，细菌的运动性和鞭毛蛋白的丰度显著降低。为了鉴定参与这种负调控的基因，我们使用运动性作为筛选表型，对 P. syringae pv. maculicola ES4326 进行了正向遗传筛选。我们鉴定出周质蛋白酶 AlgW 是鞭毛蛋白丰度的关键负调控因子，它还正向调节藻酸盐生物合成和 III 型分泌系统。我们还证明 AlgW 是丁香假单胞菌的主要毒力决定因子，它需要减弱植物的免疫反应。我们的研究结果支持这样的结论，即丁香假单胞菌通过 AlgW 协调调节毒力策略，以有效地抑制宿主免疫。
