Deng Xing-Guang, Zhu Tong, Peng Xing-Ji, Xi De-Hui, Guo Hongqing, Yin Yanhai, Zhang Da-Wei, Lin Hong-Hui
Ministry of Education Key Laboratory for Bio-Resource and Eco-Environment, College of Life Science, State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu, Sichuan, 610064, China.
Department of Genetics, Development and Cell Biology, Plant Science Institute, Iowa State University, Ames, IA 50011, USA.
Sci Rep. 2016 Feb 3;6:20579. doi: 10.1038/srep20579.
Plant steroid hormones, brassinosteroids (BRs), play essential roles in plant growth, development and stress responses. However, mechanisms by which BRs interfere with plant resistance to virus remain largely unclear. In this study, we used pharmacological and genetic approaches in combination with infection experiments to investigate the role of BRs in plant defense against Tobacco Mosaic Virus (TMV) in Nicotiana benthamiana. Exogenous applied BRs enhanced plant resistance to virus infection, while application of Bikinin (inhibitor of glycogen synthase kinase-3), which activated BR signaling, increased virus susceptibility. Silencing of NbBRI1 and NbBSK1 blocked BR-induced TMV resistance, and silencing of NbBES1/BZR1 blocked Bikinin-reduced TMV resistance. Silencing of NbMEK2, NbSIPK and NbRBOHB all compromised BR-induced virus resistance and defense-associated genes expression. Furthermore, we found MEK2-SIPK cascade activated while BES1/BZR1 inhibited RBOHB-dependent ROS production, defense gene expression and virus resistance induced by BRs. Thus, our results revealed BR signaling had two opposite effects on viral defense response. On the one hand, BRs enhanced virus resistance through MEK2-SIPK cascade and RBOHB-dependent ROS burst. On the other hand, BES1/BZR1 inhibited RBOHB-dependent ROS production and acted as an important mediator of the trade-off between growth and immunity in BR signaling.
植物类固醇激素油菜素甾醇（BRs）在植物生长、发育和应激反应中发挥着重要作用。然而，BRs干扰植物抗病毒能力的机制在很大程度上仍不清楚。在本研究中，我们结合药理学和遗传学方法以及感染实验，研究了BRs在本氏烟草对烟草花叶病毒（TMV）的植物防御中的作用。外源施用BRs增强了植物对病毒感染的抗性，而施用激活BR信号的糖原合酶激酶-3抑制剂Bikinin则增加了病毒易感性。沉默NbBRI1和NbBSK1可阻断BR诱导的TMV抗性，沉默NbBES1/BZR1可阻断Bikinin降低的TMV抗性。沉默NbMEK2、NbSIPK和NbRBOHB均损害了BR诱导的病毒抗性和防御相关基因的表达。此外，我们发现MEK2-SIPK级联被激活，而BES1/BZR1抑制了BR诱导的RBOHB依赖性活性氧（ROS）产生、防御基因表达和病毒抗性。因此，我们的结果揭示了BR信号对病毒防御反应有两种相反的作用。一方面，BRs通过MEK2-SIPK级联和RBOHB依赖性ROS爆发增强病毒抗性。另一方面，BES1/BZR1抑制RBOHB依赖性ROS产生，并在BR信号中作为生长与免疫权衡的重要调节因子。
