MiRNA duplex structure controls secondary siRNA formation

Plant secondary siRNA production determined by microRNA-duplex structure.

Out in PNAS by Manavella and colleagues: Plant secondary siRNA production determined by microRNA-duplex structure. In plants, miRNA-mediated cleavage of a target triggers in some cases the production of secondary small interfering RNAs (siRNAs), which in turn can silence other genes in trans, a phenomenon called transitivity. Several groups reported in 2010 that 22-nt miRNAs are sufficient, but not essential for generating secondary siRNAs. In this paper, we show that transitivity can be triggered when the small RNA that is not retained in AGO is 22-nt long. Moreover, we demonstrate that asymmetrically positioned bulged bases in the miRNA:miRNA* duplex, regardless of miRNA or miRNA* length, are sufficient for the initiation of transitivity. We propose that the RNA-induced silencing complex reprogramming occurs during the early steps of miRNA loading, before the miRNA duplex is disassembled and the guide strand is selected.