MicroRNAs and Their Role in Salt Stress Response in Plants

MicroRNAs (miRNAs) are a subset of endogenous approximate 22 nucleotide (nt) small non-coding regulatory RNA molecules that regulate gene expression post-transcriptionally, by mediating mRNA degradation or translational repression in a sequence specific manner. These small regulatory molecules are involved in regulating the intrinsic normal growth of cells and development of organisms as well as in maintaining the integrity of genomes. The plant miRNA research gained momentum, 2002 onwards, which was accompanied by the discovery of plant proteins involved in miRNA biogenesis. Early discovery of miRNAs has been implicated in the regulation of developmental processes. Since then much has been discovered about their involvement in plant responses to adverse environmental conditions, including abiotic stress. Various approaches of miRNAs discovery such as cloning, deep sequencing and prediction using bioinformatic tools have been adapted to learn more about the miRNA expression patterns during stress. The master regulators such as miRNAs having important role in salt stress response are very much crucial to understand the molecular regulation of stress adaptation. Many target genes of miRNAs encode transcription factors, each of which further regulates a set of downstream genes and affect physiological responses. This chapter contains a concise account on historical importance of miRNAs discovery. The miRNA biogenesis pathway and the associated proteins are also discussed along with the tools of miRNAs prediction and identification. In addition, the role of plant miRNAs and their target in plant metabolism and in particular salt stress is elaborated. With the growing knowledge on salt responsive miRNAs, the efforts to develop salt stress tolerance using miRNAs are also given.