Functions of microRNAs and related small RNAs in plants.

MicroRNAs (miRNAs) and short interfering RNAs (siRNAs), 20- to 27-nt in length, are essential regulatory molecules that act as sequence-specific guides in several processes in most eukaryotes (with the notable exception of the yeast Saccharomyces cerevisiae). These processes include DNA elimination, heterochromatin assembly, mRNA cleavage and translational repression. This review focuses on the regulatory roles of plant miRNAs during development, in the adaptive response to stresses and in the miRNA pathway itself. This review also covers the regulatory roles of two classes of endogenous plant siRNAs, ta-siRNAs and nat-siRNAs, which participate in post-transcriptional control of gene expression.