Orchestration of GSM1 and MOS2 in microRNA biogenesis and plant growth in Arabidopsis.

GSM1, a potential DEAH-box RNA helicase, is involved in the glucose-ABA signaling pathway and RNA silencing. Here, MOS2 was identified to interact with GSM1 in the nucleus, and the G-patch domain of MOS2 promoted RNA helicase activity of GSM1 in vitro. In gsm1-2, reduced levels of several miRNAs and increased levels of their respective target genes were observed. The lack of MOS2 in gsm1-2 (gsm1-2 mos2-3) severely inhibited growth, resulting in seedling lethality and greater reduction of some miRNA levels, implying a genetic interaction between GSM1 and MOS2. HYL1 encodes a double-stranded RNA-binding protein that functions in the DCL1 complex to facilitate pri-miRNA processing. By contrast, gsm1-2 hyl1-2 strongly resembled hyl1-2 in the dwarf phenotype, and the expression levels of several mature miRNAs in gsm1-2 hyl1-2 were comparable to those in hyl1-2, but lower than in gsm1-2. Impaired D-body localization of HYL1 was also observed in gsm1-2, which was detected previously in mos2-2. Moreover, HYL1-pre-miR159a binding affinity was reduced in the presence of GSM1 in vitro. Collectively, these results suggest that GSM1 and MOS2 contribute to miRNA biogenesis, which is largely associated with HYL1-engaged pri-miRNA processing.