MicroRNAs (
miRNAs) are small regulatory RNAs processed from
primary miRNA transcripts, and plant
miRNAs play important roles in plant growth, development, and response to
infection by microbes. Microbial
infections broadly alter
miRNA biogenesis, but the underlying mechanisms remain poorly understood. In this study, we report that the Rice stripe virus (RSV)-encoded nonstructural
protein 3 (NS3) interacts with OsDRB1, an indispensable component of the rice (Oryza sativa)
miRNA-processing complex. Moreover, the NS3-OsDRB1 interaction occurs at the sites required for OsDRB1 self-interaction, which is essential for
miRNA biogenesis. Further analysis revealed that NS3 acts as a scaffold between OsDRB1 and pri-
miRNAs to regulate their association and
aids in vivo processing of pri-
miRNAs. Genetic evidence in Arabidopsis showed that NS3 can partially substitute for the function of double-stranded RNA binding domain (dsRBD) of AtDRB1/AtHYL1 during
miRNA biogenesis. As a result, NS3 induces the accumulation of several
miRNAs, most of which target pivotal genes associated with development or pathogen resistance. In contrast, a mutant version of NS3 (mNS3), which still associated with OsDRB1 but has defects in
pri-miRNA binding, reduces accumulation of these
miRNAs. Transgenic rice lines expressing NS3 exhibited significantly higher susceptibility to
RSV infection compared with non-transgenic wild-type plants, whereas the transgenic lines expressing mNS3 showed a less-sensitive response. Our findings revealed a previously unknown mechanism in which a
viral protein hijacks OsDRB1, a key component of the processing complex, for
miRNA biogenesis and enhances
viral infection and pathogenesis in rice.