MicroRNA (miRNA) and small interfering RNA (siRNA): Biogenesis and functions in plants

Abstract

Small RNA was first identified in 1981 in the genetic screening of Caenorhabditis elegans. Functions of these RNA are to repress gene expression by base pairing with complementary sequences within gene. Therefore, regulation by these small RNAs is called as RNA silencing, gene silencing or RNA interference (RNAi). Till date various kinds of small RNA have been discovered and categorized on the basis of their origin, biogenesis and functions. RNase III type of ribonuclease enzymes, i.e. dicers, is involved in small RNA processing, along with many other enzymes. Small RNAs are classified broadly into two classes, microRNAs (miRNAs) and small interfering RNAs (siRNAs) according to their origin. These small RNAs are further classified on the basis of their mechanism of gene silencing, cleavage of complementary mRNA, translational repression, transcriptional repression and DNA elimination through histone modification. These small-sized RNAs have bigger and vital roles to play in plants, which pertain to gene regulation during biotic stress and abiotic stress and development. Small RNA also plays a role in the plant defence against viruses and transposable elements.