Functional Analysis Of OsRDR1Responsive To RSV Infection

Small RNA-mediated gene silencing controls the gene expression responsible for growth and development and the response to biotic and abiotic stresses in eukaryotes. Numerous studies have shown that the silencing machinery contains several key factors, including Argonautes (AGOs), Dicers (DCRs) or Dicer-like (DCLs), and RNA-dependent RNA Polymerases (RdRPs). In Arabidopsis thaliana, a model dicotyledonous plant, RNA-dependent RNA polymerases (RdRPs) or their homologues have been implicated in the RNA silencing or antiviral pathway but little is known about their function in rice plants.In this study, the OsRDR1gene was firstly amplified, cloned and sequenced from rice plants. Sequence analysis showed that OsRDRl contained five exons and four introns and quantitative analysis showed that its expression was induced by rice stripe virus (RSV) infection, suggesting that it may have a function associated with viral resistance in rice plants. Furthermore a rice retrotransposon Tos17insertion mutant line ND2001of cv. Nipponbar, was confirmed by both PCR and RT-PCR to be an Osrdrl mutant, in which the OsRDRl gene was fully knocked out. The mutant rice plants were previously shown to be more susceptible to RSV than wild type rice plants. To explore the functions of the OsRDRl gene in rice antiviral defense, deep sequencing was used to survey the RSV virus-derived small RNAs (vsRNAs) from RSV-infected Osrdrl mutant and wild type rice plants. Both the mutant and wild-type plants had large amounts of vsRNAs, which could be mapped well to the genomic or antigenomic strands of RNAs1-4of RSV, but the numbers of vsRNAs were globally and significantly reduced in Osrdrl mutant plants compared to the wild type. These results indicate that OsRDRl may be required for host antiviral defense and provides compelling evidence that OsRDR1is involved in the biogenesis of vsRNAs.