title: RNAi-mediated viral immunity requires amplification of virus-derived siRNAs in Arabidopsis thaliana.
abstract: In diverse eukaryotic organisms, Dicer-processed, virus-derived small interfering RNAs direct antiviral immunity by RNA silencing or RNA interference. Here we show that in addition to core dicing and slicing components of RNAi, the RNAi-mediated viral immunity in Arabidopsis thaliana requires host RNA-directed RNA polymerase (RDR) 1 or RDR6 to produce viral secondary siRNAs following viral RNA replication-triggered biogenesis of primary siRNAs. We found that the two antiviral RDRs exhibited specificity in targeting the tripartite positive-strand RNA genome of cucumber mosaic virus (CMV). RDR1 preferentially amplified the 5'-terminal siRNAs of each of the three viral genomic RNAs, whereas an increased production of siRNAs targeting the 3' half of RNA3 detected in rdr1 mutant plants appeared to be RDR6-dependent. However, siRNAs derived from a single-stranded 336-nucleotide satellite RNA of CMV were not amplified by either antiviral RDR, suggesting avoidance of the potent RDR-dependent silencing as a strategy for the molecular parasite of CMV to achieve preferential replication. Our work thus identifies a distinct mechanism for the amplification of immunity effectors, which together with the requirement for the biogenesis of endogenous siRNAs, may play a role in the emergence and expansion of eukaryotic RDRs.
authors: Center for Plant Cell Biology, Department of Plant Pathology and Microbiology, University of California, Riverside, CA 92521, USA.
authors: Xian-Bing
authors: XB
authors: Wang
authors: Qingfa
authors: Q
authors: Wu
authors: Takao
authors: T
authors: Ito
authors: Fabrizio
authors: F
authors: Cillo
authors: Wan-Xiang
authors: WX
authors: Li
authors: Xuemei
authors: X
authors: Chen
authors: Jia-Lin
authors: JL
authors: Yu
authors: Shou-Wei
authors: SW
authors: Ding
mesh_terms: D000818:Animals; D017360:Arabidopsis / Q000235:genetics / Q000276:immunology / Q000821:virology; D017799:Cucumovirus / Q000235:genetics / Q000378:metabolism; D020869:Gene Expression Profiling; D015967:Gene Expression Regulation, Viral; D020868:Gene Silencing; D007109:Immunity / Q000235:genetics*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D010935:Plant Diseases / Q000235:genetics / Q000821:virology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism*; D012367:RNA, Viral / Q000235:genetics / Q000378:metabolism*; D012324:RNA-Dependent RNA Polymerase / Q000235:genetics / Q000378:metabolism; D043244:Ribonuclease III / Q000235:genetics / Q000378:metabolism; D014777:Virus Diseases / Q000235:genetics / Q000821:virology; D014779:Virus Replication / Q000235:genetics
chemical_list: D007527:Isoenzymes; D010940:Plant Proteins; D034741:RNA, Small Interfering; D012367:RNA, Viral; D012324:RNA-Dependent RNA Polymerase; D043244:Ribonuclease III