Ji L H, Ding S W
Molecular Virology Laboratory, Institute of Molecular Agrobiology, National University of Singapore, Singapore.
Mol Plant Microbe Interact. 2001 Jun;14(6):715-24. doi: 10.1094/MPMI.2001.14.6.715.
The Cucumber mosaic virus (CMV)-encoded 2b protein (Cmv2b) is a nuclear protein that suppresses transgene RNA silencing in Nicotiana benthamiana. Cmv2b is an important virulence determinant but nonessential for systemic spread in N. glutinosa, in contrast to its indispensable role for systemic infections in cucumber. Here, we report that Cmv2b became essential for systemic infections in older N. glutinosa plants or in young seedlings pretreated with salicylic acid (SA). Expression of Cmv2b from the genome of either CMV or Tobacco mosaic virus significantly reduced the inhibitory effect of SA on virus accumulation in inoculated leaves and systemic leaves. A close correlation is demonstrated between Cmv2b expression and a reduced SA-dependent induction of the alternative oxidase gene, a component of the recently proposed SA-regulated antiviral defense. These results collectively reveal a novel activity of Cmv2b in the inhibition of SA-mediated virus resistance. We used a N. tabacum line expressing a bacterial nahG transgene that degrades SA to provide evidence for a Cmv2b-sensitive antiviral defense mechanism in tobacco in which SA acts as a positive modifier but not as an essential component. We propose that SA induces virus resistance by potentiating a RNA-silencing antiviral defense that is targeted by Cmv2b.
黄瓜花叶病毒（CMV）编码的2b蛋白（Cmv2b）是一种核蛋白，可抑制本氏烟草中的转基因RNA沉默。Cmv2b是一个重要的毒力决定因素，但对粘毛烟草的系统传播并非必需，这与其在黄瓜系统感染中不可或缺的作用形成对比。在此，我们报道Cmv2b对于老龄粘毛烟草植株或用水杨酸（SA）预处理的幼苗的系统感染变得至关重要。来自CMV或烟草花叶病毒基因组的Cmv2b表达显著降低了SA对接种叶片和系统叶片中病毒积累的抑制作用。Cmv2b表达与替代氧化酶基因（最近提出的SA调节的抗病毒防御的一个组成部分）的SA依赖性诱导减少之间存在密切相关性。这些结果共同揭示了Cmv2b在抑制SA介导的病毒抗性方面的新活性。我们使用了一个表达降解SA的细菌nahG转基因的烟草品系，为烟草中一种对Cmv2b敏感的抗病毒防御机制提供证据，其中SA作为正调节因子而非必需成分发挥作用。我们提出，SA通过增强一种被Cmv2b靶向的RNA沉默抗病毒防御来诱导病毒抗性。
