Plant RNA Interference Pathways: Diversity in Function, Similarity in Action

Small non-coding RNA-mediated gene-silencing pathways, collectively called RNA interference (RNAi), are involved in regulation of endogenous gene expression and plant defence. It is manifested through two broad classes of small non-coding regulatory RNAs, small interfering RNA (siRNA) and microRNA (miRNA). siRNAs, generated from cleavage of long hairpin RNA by RNase III-class endonuclease, Dicer-like, mediate transcriptional or post-transcriptional gene silencing. At transcriptional level, 24-nucleotide (nt)-long-siRNAs guide an effector complex for DNA methylation, which leads to heterochromatinisation of target loci and consequently transcriptional silencing. At post-transcriptional level, a different size class of 21-nt-long siRNAs guides a silencing complex, called RNA-induced silencing complex, for cleavage of target mRNA. cis-acting siRNAs are involved in plant defence against viruses and transposons, and trans-acting siRNAs regulate endogenous genes involved in plant growth. miRNAs are generated from processing of imperfect stem-loop RNA precursors by Dicer-like. They regulate plant growth and adaptive stress responses by either degradation or translational repression of target mRNAs.