Abstract
RNAi is a major antiviral defense response in plant and animal model systems. RNA-dependent RNA polymerase 6 (RDR6) is an essential component of RNAi, which plays an important role in the resistance against viruses in the model plants. We found previously that rice RDR6 (OsRDR6) functioned in the defense against Rice stripe virus (RSV), and Rice Dwarf Phytoreovirus (RDV) infection resulted in down-regulation of expression of RDR6. Here we report our new findings on the function of OsRDR6 against RDV. Our result showed that down-regulation of OsRDR6 through the antisense (OsRDR6AS) strategy increased rice susceptibility to RDV infection while over-expression of OsRDR6 had no effect on RDV infection. The accumulation of RDV vsiRNAs was reduced in the OsRDR6AS plants. In the OsRDR6 over-expressed plants, the levels of OsRDR6 RNA transcript and protein were much higher than that in the control plants. Interestingly, the accumulation level of OsRDR6 protein became undetectable after RDV infection. This finding indicated that the translation and/or stability of OsRDR6 protein were negatively impacted upon RDV infection. This new finding provides a new light on the function of RDR6 in plant defense response and the cross-talking between factors encoded by host plant and double-stranded RNA viruses.
Highlights
RNA silencing functions as a potent antiviral pathway in plant and animal systems[1,2,3,4,5,6], and is known to be triggered by the accumulation of double-stranded viral RNA
By 7wpi, the Rice Dwarf Phytoreovirus (RDV) infection rate in the three OsRDR6AS transgenic lines reached above 90% while the infection rate of the wild type (WT) plants was about 80%, indicating that down-regulation of OsRDR6 expression in rice increased the susceptibility to RDV infection
Further study by Zhu et al showed that RNA-dependent RNA polymerase 6 (RDR6)-dependent silencing of Cucumber mosaic virus (CMV) in N. benthamiana was initiated by CMV Satellite RNA-derived small interfering RNA known as satsiR-1249
Summary
RNA silencing functions as a potent antiviral pathway in plant and animal systems[1,2,3,4,5,6], and is known to be triggered by the accumulation of double-stranded viral RNA (dsRNA). RDR1 plays an important role in production and amplification of both exogenous vsiRNAs and endogenous viral activated siRNA (vasiRNA) in plants infected with positive-stranded viruses[15,16,17]. Recent studies on the dicotyledonous model plant A. thaliana and N. benthamiana have demonstrated the significant role of RDR6 in host defense response against some positive-sense single-stranded RNA viruses[28,29], as well as viroid[30,31]. OsRDR1 is required for the production of small RNA in response to DNA-damage in rice[45] and for the RNA silencing mediated by Brome mosaic bromovirus (BMV), but not by Wheat dwarf geminivirus (WDV)[46]. OsRDR6 is known to play roles in the defense response against dsRNA virus infection in monocot plants, how dsRNA viruses counteract this host defense strategy remains largely unknown. Our finding presented in this paper provides some new insights into the function of OsRDR6 in defense response against dsRNA virus infection, and the defense and counter-defense reaction between host plant and virus
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