Pathogenicity of Xanthomonas and most other Gram-negative phytopathogenic bacteria depends on a conserved type III secretion (T3S) system which injects several different effector proteins into the plant cell. Extensive studies in the last years on the molecular mechanisms of type III effector function revealed that effector proteins with enzymatic functions seem to play important roles in the interaction of Xanthomonas with its host plants. In addition, Xanthomonas express a unique class of type III effectors to pursue another strategy. Effectors of the AvrBs3 family, so far only identified in Xanthomonas spp. and Ralstonia solanacearum, mimic plant transcriptional activators and manipulate the plant transcriptome.%黄单胞菌借助保守的 III 型分泌系统，将多个效应蛋白注入植物细胞，克服宿主的防卫，利于黄单胞菌在植物体内发挥毒性功能。最近对 III 型效应蛋白致病机理开展了大量研究，结果发现具有酶功能的效应蛋白在黄单胞菌及其宿主间的相互作用中发挥非常重要的作用。此外，黄单胞菌存在一类独特的 III 型效应蛋白(AvrBs3家族)。迄今为止，仅在黄单胞菌和雷尔氏菌(Ralstonia solanacearum)中发现 AvrBs3家族效应蛋白， AvrBs3家族通过模拟转录激活子来操纵寄主植物易感基因的表达。
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