Institut für Genetik, Martin-Luther-Universität Halle-Wittenberg, 06099 Halle, Germany.
Mol Plant Pathol. 2001 Sep 1;2(5):287-96. doi: 10.1046/j.1464-6722.2001.00077.x.
summary The hrp gene cluster of the plant pathogen Xanthomonas campestris pv. vesicatoria (Xcv) encodes a type III secretion system required for the delivery of virulence and avirulence proteins into the plant. Some of these effector proteins, e.g. AvrBs1 and AvrBsT, are recognized by pepper plants carrying corresponding resistance genes, triggering the hypersensitive reaction (HR). In this study, epitope tagged AvrBs1 and AvrBsT proteins were detected in culture supernatants only in the presence of a functional type III apparatus and not in a hrcV mutant, showing that both proteins are secreted by Xcv in an hrp-dependent manner. Expression of both avirulence genes is constitutive and independent of the hrp gene regulators, hrpG and hrpX. Transient expression of avrBs1 and avrBsT in resistant host plants using Agrobacterium tumefaciens-mediated gene transfer resulted in the induction of a specific HR. This indicates that recognition occurs intracellularly, and suggests that during the Xcv infection, AvrBs1 and AvrBsT are translocated from Xcv into the plant cell. We describe a conserved protein motif which is present in the N-terminal region of all known Xcv avirulence proteins and discuss its potential role in translocation into plant cells.
摘要 植物病原菌黄单胞菌野油菜致病变种（Xcv）的 hrp 基因簇编码一种 III 型分泌系统，该系统将毒力和无毒蛋白输送到植物中。这些效应蛋白中的一些，如 AvrBs1 和 AvrBsT，被携带相应抗性基因的辣椒植株识别，触发过敏反应（HR）。在这项研究中，仅在存在功能 III 型装置的情况下，在 hrcV 突变体中未检测到带有表位标签的 AvrBs1 和 AvrBsT 蛋白，表明这两种蛋白均由 Xcv 以依赖于 hrp 的方式分泌。两种无毒基因的表达均为组成型，与 hrp 基因调节剂 hrpG 和 hrpX 无关。使用根癌农杆菌介导的基因转移在抗性宿主植物中瞬时表达 avrBs1 和 avrBsT 导致特异性 HR 的诱导。这表明识别发生在细胞内，并且表明在 Xcv 感染期间，AvrBs1 和 AvrBsT 从 Xcv 易位到植物细胞中。我们描述了一个保守的蛋白基序，存在于所有已知的 Xcv 无毒蛋白的 N 端区域，并讨论了其在易位到植物细胞中的潜在作用。
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