Insight into Small RNA biogenesis and their functions in plants.

Abstract : The term ‘epigenetic’ was first coined by Waddington more than half a century ago. Now, it has emerged as a broad field of science that investigates a myriad of biological phenomena governed by novel molecular mechanisms. Epigenetics works on two levels, at the DNA level, methylation of cytosines that is context dependent and reversible plays a crucial role especially if the modification is in the promoter regions of transcription units. Cytosine methylation is context independent in plants and controls transposons and unruly elements in genomes. The second level of epigenetics is at the level of DNA bound histones. Many of the histone-modifying proteins have been characterized, although still many more remain to be discovered and the sequence/priority order of the histone modifications are being elucidated. Small regulatory RNAs play an essential role in establishment and maintenance of DNA methylation among plants termed as ‘RNA directed DNA methylation’ (RdDM). In animals, the developmental program is planned in the embryo but in plants, it is designed post-embryonically through a poorly understood mechanism and early indications are that epigenetic variations play a massive role in such programming. Small RNA directed DNA methylation and subsequent inheritance (epigenetics) has unparalleled implications for plant development and their survival against a variety of stresses. Our lab focuses on various aspects of small RNA biogenesis, their action on complementary RNAs/DNAs and the nature of ribo-nucleoprotein machineries that are part of these processes. Results from our lab and from those of others indicate how plant phenotypes are influenced by small RNAs, RdDM and epigenetics. I will also discuss roles of these pathways on various aspects of plant development taking examples from less conserved small RNAs that regulate clade/family specific phenotypes.