Yan Xia, Tao Jun, Luo Hong-Li, Tan Lei-Tao, Rong Wei, Li Hui-Ping, He Chao-Zu
Institute of Tropical Agriculture and Forestry, Hainan University, Haikou 570228, China; Hainan Key Laboratory for Sustainable Utilization of Tropical Bioresources, Haikou 570228, China.
Res Microbiol. 2019 Apr-May;170(3):138-146. doi: 10.1016/j.resmic.2018.12.001. Epub 2018 Dec 27.
Xanthomonas campestris pv. campestris (Xcc) secretes a suite of effectors into host plants via the type III secretion system (T3SS), modulating plant immunity defenses. Strain Xcc8004 causes black rot in brassica plants, including Arabidopsis thaliana, making it a classical model for the study of Xanthomonas pathogenesis. XopL was defined as a T3SS effector (T3SE) since its homologues XopL from Xanthomonas campestris pv. vesicatoria (Xcv85-10) contribute to virulence in host plants. Except for its virulence on Chinese radish plants, little was previously known about the regulation and function of XopL. Here, we tested the role of XopL in the pathogenicity of Xcc8004 on different host plants including Arabidopsis. We found that it was required for full virulence of Xcc8004 in Chinese cabbage. XopL promoted bacterial infection in Arabidopsis and suppressed bacterial flagellin (flg22)-induced FRK1 transcription, reactive oxygen species (ROS) burst, callose deposition, and pathogenesis-related marker gene expression, but it did not affect mitogen-activated protein kinases (MAPKs) cascade. Early and prolonged expression of XopL affected Arabidopsis growth and development. We demonstrated that XopL is a virulence factor and interferes with innate immunity of Arabidopsis by suppressing pathogen-associated molecular pattern-triggered immunity (PTI) signaling, independent of MAPKs.
野油菜黄单胞菌野油菜致病变种（Xcc）通过III型分泌系统（T3SS）向宿主植物分泌一系列效应蛋白，从而调节植物的免疫防御。Xcc8004菌株会在包括拟南芥在内的芸苔属植物中引发黑腐病，使其成为研究黄单胞菌致病机制的经典模型。XopL被定义为一种III型分泌系统效应蛋白（T3SE），因为其来自野油菜黄单胞菌疮痂致病变种（Xcv85-10）的同源物XopL有助于宿主植物的致病力。除了其对萝卜植株的致病力外，此前人们对XopL的调控和功能了解甚少。在此，我们测试了XopL在Xcc8004对包括拟南芥在内的不同宿主植物致病过程中的作用。我们发现，它是Xcc8004在大白菜中充分致病所必需的。XopL促进了拟南芥中的细菌感染，并抑制了细菌鞭毛蛋白（flg22）诱导的FRK1转录、活性氧（ROS）爆发、胼胝质沉积以及病程相关标记基因的表达，但它不影响丝裂原活化蛋白激酶（MAPKs）级联反应。XopL的早期和持续表达影响了拟南芥的生长发育。我们证明，XopL是一种致病因子，通过抑制病原体相关分子模式触发的免疫（PTI）信号传导来干扰拟南芥的先天免疫，且不依赖于MAPKs。
