Ramesh SV
Small non-coding RNAs (sncRNAs) are potent regulators of indispensable biological functions such as gene expression, maintenance of chromatin status, defence against invading nucleic acids like viruses, transposons etc in plants and animals. sncRNA repertoire of plants comprises small interfering RNAs (siRNAs) and microRNAs (miRNAs) as ultimate regulators of gene expression pathways. First small ncRNA (lin-4) with a role in post-transcriptional gene silencing (PTGS) was discovered way back in 1993 in C. elegans [1]. Nonetheless, it was not until 1998 the basic phenomenon of sequence dependent RNA based gene silencing or RNA interference (RNAi) itself was uncovered. Later on, the significance of sRNAs especially, miRNAs and their role in multitude of host developmental and growth activities including response to biotic and abiotic stresses were reported. miRNAs downregulate expression of cognate mRNAs that exhibit sequence complementary thereby functions as negative regulators of such genes. Hence under the influence of stress, miRNAs that are upregulated lead to repression of cognate mRNAs whereas miRNAs whose levels are suppressed result in abundant target mRNAs which may assist the plants tide over adverse stress conditions.