Small RNAs in Plants

Abstract

Small RNAs associated with RNA silencing have emerged as an essential regulatory component in eukaryotes. Although their widespread existence was revealed only a decade ago, remarkable progress has been made toward our understanding of their biogenesis and cellular function. In plants, the small RNA-mediated regulatory mechanisms are involved in many important biological processes including developmental timing, pattern formation, epigenetic silencing of transposable elements, response to environmental stress, and defense against invading pathogens. Emerging evidence also indicates the involvement of small RNAs in epigenetic reprogramming associated with germ cell and embryo development during sexual reproduction. In this chapter, we provide an overview on the conserved molecular machinery that has evolved to give rise to microRNAs (miRNAs) and several distinct classes of small interfering RNAs (siRNAs) in plants, including heterochromatin-associated siRNAs (hc-siRNAs), trans-acting siRNAs (ta-siRNAs), and natural cis-antisense transcripts-associated siRNAs (nat-siRNAs). These are followed by a description on the cellular function and regulatory targets for each class of these endogenous small RNAs. While the focus of the book is on miRNAs, it is our hope that this chapter will serve as a brief introduction to the plant small RNA world.