Small RNAs in Plants

Small RNAs associated with RNA silencing have emerged as an essen- 3 tial regulatory component in eukaryotes. Although their widespread existence was 4 revealed only a decade ago, remarkable progress has been made toward our 5 understanding of their biogenesis and cellular function. In plants, the small RNA- 6 mediated regulatory mechanisms are involved in many important biological pro- 7 cesses including developmental timing, pattern formation, epigenetic silencing of 8 transposable elements, response to environmental stress, and defense against invad- 9 ing pathogens. Emerging evidence also indicates the involvement of small RNAs in 10 epigenetic reprogramming associated with germ cell and embryo development 11 during sexual reproduction. In this chapter, we provide an overview on the 12 conserved molecular machinery that has evolved to give rise to microRNAs 13 (miRNAs) and several distinct classes of small interfering RNAs (siRNAs) in 14 plants, including heterochromatin-associate