THE SMALL RNAs OF PHYSCOMITRELLA PATENS: EXPRESSION, FUNCTION AND EVOLUTION

Information encoded by the sequential arrangement of DNA bases guides the synthesis of functional polypeptides via RNA intermediates. However, the functions ofRNAtranscend those of a mere messenger. The discovery and characterization of gene regulation orchestrated by short, non-protein-codingRNAshas revealed previously unsuspected but vast systems of gene regulation, especially in metazoans and land plants. Small silencing RNAs, which include short interfering RNAs (siRNAs) and microRNAs (miRNAs), are exceptionally diversified and numerous in plants. Their known roster of functions includes, at a minimum, development, morphogenesis, nutrient acquisition and genome defence. Recent studies of the naturally occurring small silencing RNAs of Physcomitrella patens have elucidated fundamental aspects of siRNA biogenesis and miRNA evolution. In this chapter, I describe the biogenesis and expression of miRNAs and siRNAs in P. patens, as well as their functions and evolution.