Small RNAs: Master Regulators of Epigenetic Silencing in Plants
From fairly simple beginnings, research on epigenetic silencing in plants has revealed a highly complex epigenetic pathway. In the last two decades, several interesting phenomena associated with epigenetic regulation in plants were dissected giving insights into the biological significance of epigenetic marks and the role it plays in an organism’s life cycle by controlling different physiological processes like plant development, morphogenesis, reproduction, and stress response. Epigenetics refers to either heritable or reversible genetic modifications in DNA or histone proteins that maintain the nucleosome structure in a dynamic manner or those mediated by small RNAs (sRNAs) that in turn modulate gene expression. Plants are equipped with intricate regulatory mechanism to elicit highly sequence-specific chromatin-based gene silencing. Diverse classes of RNAs like small interfering RNA (siRNA), microRNAs (miRNAs), and long noncoding RNAs (lnc RNAs) have emerged as key regulators of gene expression along with several accessory proteins. sRNAs are widespread in various eukaryotes and are specifically involved in the maintenance of chromatin modifications in plants. These sRNAs regulate gene expression in different ways including post-transcriptional gene silencing (PTGS) in cytosol by targeting complementary transcripts for degradation, thereby repressing protein synthesis. In nucleus, sRNAs are responsible for transcriptional gene silencing (TGS) by directing epigenetic modifications like cytosine or histone methylation to homologous regions of the genome. This chapter gives an overview of the role of small RNAs in PTGS and TGS.
KeywordsDNA methylation miRNAs Post-transcriptional gene silencing sRNA Transcriptional gene silencing Transposon silencing
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