The Xanthomonas outer protein C2 (XopC2) family of bacterial effectors is widely found in plant pathogens and Legionella species. However, the biochemical activity and host targets of these effectors remain enigmatic. Here we show that ectopic expression of XopC2 promotes jasmonate signaling and stomatal opening in transgenic rice plants, which are more susceptible to Xanthomonas oryzae pv. oryzicola infection. Guided by these phenotypes, we discover that XopC2 represents a family of atypical kinases that specifically phosphorylate OSK1, a universal adaptor protein of the Skp1-Cullin-F-box ubiquitin ligase complexes. Intriguingly, OSK1 phosphorylation at Ser⁵³ by XopC2 exclusively increases the binding affinity of OSK1 to the jasmonate receptor OsCOI1b, and specifically enhances the ubiquitination and degradation of JAZ transcription repressors and plant disease susceptibility through inhibiting stomatal immunity. These results define XopC2 as a prototypic member of a family of pathogenic effector kinases and highlight a smart molecular mechanism to activate jasmonate signaling.

细菌效应子黄单胞菌外部蛋白 C2 (XopC2) 家族广泛存在于植物病原体和军团菌中。然而，这些效应子的生化活性和宿主靶标仍然是个谜。在这里，我们表明 XopC2 的异位表达促进转基因水稻植物中的茉莉酸信号和气孔开放，这些植物更容易受到米黄单胞菌pv 的影响。水稻感染。在这些表型的指导下，我们发现 XopC2 代表了一个特异性磷酸化 OSK1 的非典型激酶家族，OSK1 是 Skp1-Cullin-F-box 泛素连接酶复合物的通用衔接蛋白。有趣的是，OSK1 在 Ser ^53磷酸化XopC2 专门增加 OSK1 与茉莉酸受体 OsCOI1b 的结合亲和力，并通过抑制气孔免疫特异性增强 JAZ 转录抑制因子的泛素化和降解以及植物病害易感性。这些结果将 XopC2 定义为致病效应激酶家族的原型成员，并突出了激活茉莉酸信号传导的智能分子机制。