近日，国际病毒学著名期刊Journal of Virology 在线刊登了中科院微生物研究所研究人员的最新研究成果“Satellite RNA-Derived Small Interfering RNA satsiR-12 Targeting the 3′ Untranslated Region of Cucumber Mosaic Virus Triggers Viral RNAs for Degradation，”，文章中，研究人员揭示了植物RNA沉默互作机制研究的新进展。
RNA沉默是指在真核生物中发现的由小RNA（21-30nt）介导的、以序列特异性方式引起靶标基因表达受抑的现象。在植物中，除了能调控其生长发育，RNA沉默在植物抵抗病毒的入侵中同样起着非常重要的作用。一些植物病毒侵染常伴有卫星RNA的复制，并影响辅助病毒在寄主中的致病性。
在国家重点基础研究发展计划（973计划）等项目资助下，中国科学院微生物研究所植物基因组学国家重点实验室郭惠珊研究员领导的课题组，对植物RNA沉默在寄主植物、辅助病毒和卫星RNA三者的互作调控进行了深入的研究。他们在早期通过克隆黄瓜花叶病毒（CMV）卫星RNA的小RNA，探讨了植物RNA沉默途径对卫星RNA的靶向作用（Du et al.， 2007. Journal of Virology）。进一步研究发现，卫星RNA通过下调CMV编码的RNA沉默抑制子蛋白（CMV-2b），从而减轻CMV感染寄主的病症（Hou et al.， 2011. Molecular Plant Pathology）。
最近，通过对卫星RNA小RNA的生物学活性和功能的研究，他们发现一个卫星RNA的小RNA（satsiR-12）靶向CMV RNA 的3’UTR，引发植物依赖的RNA聚合酶RDR6的抗病毒沉默作用；而CMV-2b蛋白对这种由satsiR-12-介导的依赖RDR6的下调病毒RNA作用具有抑制效应；突变和野生型病毒的竞争性实验进一步证实，在CMV自然侵染的条件下，卫星RNA的小RNA参与了RNA沉默调控辅助病毒RNA的表达。
该研究在国际上首次直接证明了病原来源的小RNA参与调控病毒RNA的生物学功能，揭示了寄主-辅助病毒-卫星RNA在RNA沉默层面上复杂的互作调控机制，体现了卫星RNA及其与辅助病毒和寄主的协同性进化。（生物谷Bioon.com）
doi:10.1128/JVI.05806-11
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Satellite RNA-Derived Small Interfering RNA satsiR-12 Targeting the 3′ Untranslated Region of Cucumber Mosaic Virus Triggers Viral RNAs for Degradation
Hui Zhu1,2, Cheng-Guo Duan1, Wei-Na Hou1, Quan-Sheng Du1, Dian-Qiu Lv1,3, Rong-Xiang Fang1 and Hui-Shan Guo1,*
RNA silencing provides protection against RNA viruses by targeting both the helper virus and its satellite RNA (satRNA). Virus-derived small interfering RNAs (vsiRNAs) bound with Argonaute (AGO) proteins are presumed participants in the silencing process. Here, we show that a vsiRNA targeted to virus RNAs triggers the host RNA-dependent RNA polymerase 6 (RDR6)-mediated degradation of viral RNAs. We confirmed that satRNA-derived small interfering RNAs (satsiRNAs) could be associated with different AGO proteins in planta. The most frequently cloned satsiRNA, satsiR-12, was predicted to imperfectly match to Cucumber mosaic virus (CMV) RNAs in the upstream area of the 3′ untranslated region (3′ UTR). Moreover, an artificial satsiR-12 (asatsiR-12) mediated cleavage of a green fluorescent protein (GFP) sensor construct harboring the satsiR-12 target site. asatsiR-12 also mediated reduction of viral RNAs in 2b-deficient CMV (CMVΔ2b)-infected Nicotiana benthamiana. The reduction was not observed in CMVΔ2b-infected RDR6i plants, in which RDR6 was silenced. Following infection with 2b-containing CMV, the reduction in viral RNAs was not observed in plants of either genotype, indicating that the asatsiR-12-mediated reduction of viral RNAs in the presence of RDR6 was inhibited by the 2b protein. Our results suggest that satsiR-12 targeting the 3′ UTR of CMV RNAs triggered RDR6-dependent antiviral silencing. Competition experiments with wild-type CMV RNAs and anti-satsiR-12 mutant RNA1 in the presence of 2b and satRNA demonstrate the inhibitory effect of the 2b protein on the satsiR-12-related degradation of CMV RNAs, revealing a substantial suppressor function of the 2b protein in native CMV infection. Our data provide evidence for the important biological functions of satsiRNAs in homeostatic interactions among the host, virus, and satRNA in the final outcome of viral infection.
