Hainan Key Laboratory for Sustainable Utilization of Tropical Bioresources, College of Tropical Crops, Hainan University, Haikou, Hainan, China.
Mol Plant Pathol. 2022 Mar;23(3):355-369. doi: 10.1111/mpp.13164. Epub 2021 Nov 27.
Xanthomonas campestris pv. campestris (Xcc) can cause black rot in cruciferous plants worldwide. Two-component systems (TCSs) are key for bacterial adaptation to various environments, including hosts. VemR is a TCS response regulator and crucial for Xcc motility and virulence. Here, we report that RavA is the cognate histidine kinase (HK) of VemR and elucidate the signalling pathway by which VemR regulates Xcc motility and virulence. Genetic analysis showed that VemR is epistatic to RavA. Using bacterial two-hybrid experiments and pull-down and phosphorylation assays, we found that RavA can interact with and phosphorylate VemR, suggesting that RavA is the cognate HK of VemR. In addition, we found that RpoN2 and FleQ are epistatic to VemR in regulating bacterial motility and virulence. In vivo and in vitro experiments demonstrated that VemR interacts with FleQ but not with RpoN2. RavA/VemR regulates the expression of the flagellin-encoding gene fliC by activating the transcription of the rpoN2-vemR-fleQ and flhF-fleN-fliA operons. In summary, our data show that the RavA/VemR TCS regulates FleQ activity and thus influences the expression of motility-related genes, thereby affecting Xcc motility and virulence. The identification of this novel signalling pathway will deepen our understanding of Xcc-plant interactions.
野油菜黄单胞菌野油菜致病变种（Xcc）可引起世界各地十字花科植物的黑腐病。双组分系统（TCS）是细菌适应各种环境（包括宿主）的关键。VemR 是一种 TCS 响应调节剂，对 Xcc 的运动性和毒性至关重要。在这里，我们报告 RavA 是 VemR 的同源组氨酸激酶（HK），并阐明了 VemR 调节 Xcc 运动性和毒性的信号通路。遗传分析表明 VemR 与 RavA 是上位关系。通过细菌双杂交实验、下拉和磷酸化实验，我们发现 RavA 可以与 VemR 相互作用并磷酸化 VemR，表明 RavA 是 VemR 的同源 HK。此外，我们发现 RpoN2 和 FleQ 在调节细菌运动性和毒性方面与 VemR 是上位关系。体内和体外实验表明 VemR 与 FleQ 相互作用，而不与 RpoN2 相互作用。RavA/VemR 通过激活 rpoN2-vemR-fleQ 和 flhF-fleN-fliA 操纵子的转录来调节鞭毛蛋白编码基因 fliC 的表达。总之，我们的数据表明 RavA/VemR TCS 调节 FleQ 活性，从而影响运动相关基因的表达，从而影响 Xcc 的运动性和毒性。该信号通路的鉴定将加深我们对 Xcc-植物相互作用的理解。
