Introduction to plant small RNAs

Abstract Small RNAs are a group of 20–30 nucleotide noncoding RNAs that function as key epigenetic regulators by transcriptionally and/or post-transcriptionally regulating gene expression in eukaryotes. In 1993, the first small RNA was discovered in the nematode Caenorhabditis elegans; since then, numerous small RNAs and their essential roles in almost all aspects of biological processes have been uncovered in diverse animals and plants. In plants, the major molecular frameworks of small RNA biogenesis and their modes of action have been established, and their broad effects have also been extensively investigated. In this chapter, we summarize the current knowledge on the three major types of plant small RNAs: microRNAs, small interfering RNAs, and phased small interfering RNAs, with a focus on their biogenesis, modes of action, and local and systemic movement, as well as their regulatory function in plant development.