RNA interference (RNAi) is a double-stranded (ds)RNA-inducible, sequence-specific RNA-degradation mechanism that operates as a natural antiviral system in plants and animals. Successful virus infection requires evasion or suppression of RNAi. Indeed, RNAi suppressor proteins have been identified in plant and animal viruses, although the molecular mechanism of silencing inhibition is still poorly understood. Because many RNA viruses encode dsRNA-binding proteins (dsRBPs) and as RNAi is triggered by the accumulation of dsRNAs, dsRBPs were examined to see if they inhibit RNAi. Here, it is shown that heterologous dsRBPs suppressed RNAi in plants, indicating that in natural host-virus interactions, pathogen-encoded dsRBPs could inactivate RNAi-mediated host defences.
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