Ribosome stalling caused by the Argonaute-miRNA-SGS3 complex regulates production of secondary siRNA biogenesis in plants

The path of ribosomes on mRNAs can be impeded by various obstacles. One such example is halting of ribosome movement by microRNAs, though the exact mechanism and physiological role remain unclear. Here, we find that ribosome stalling caused by the Argonaute-miRNA-SGS3 complex regulates production of secondary siRNA biogenesis in plants. We show that the double-stranded RNA-binding protein, SGS3, directly interacts with the 3' end of the microRNA-Argonaute complex, resulting in ribosome stalling. Strikingly, microRNA-mediated ribosome stalling enhances production of secondary small interfering RNAs (siRNAs) from target mRNAs. Our results uncover a previously uncharacterized role for paused ribosomes in regulation of small RNA function that may have broad biological implications across the plant kingdom.