Mechanisms that regulate the production of secondary siRNAs in plants

Many organisms produce secondary small interfering RNAs (siRNAs) that are triggered by primary small RNAs to regulate various biological processes. Plants have evolved several types of secondary siRNA biogenesis pathways that play important roles in development, stress responses and defense against viruses and transposons. The critical step of these pathways is the production of double-stranded RNAs by RNA-dependent RNA polymerases. This step is normally tightly regulated, but when its control is released, secondary siRNA production is initiated. In this article, we will review the recent advances in secondary siRNA production triggered by microRNAs encoded in the genome and siRNAs derived from invasive nucleic acids. In particular, we will focus on the factors, events, and RNA/DNA elements that promote or inhibit the early steps of secondary siRNA biogenesis. Graphical Abstract

Automated summary

Many organisms produce secondary siRNAs to regulate biological processes, and plants have evolved various pathways for secondary siRNA production. The critical step is the production of double-stranded RNAs by RNA-dependent RNA polymerases. This article reviews recent advances in secondary siRNA production triggered by microRNAs and invasive nucleic acids, focusing on factors, events, and RNA/DNA elements that promote or inhibit the early steps of biogenesis.