Role of MicroRNAs in Abiotic and Biotic Stress Resistance in Plants

Plants in their natural habitat are exposed to adverse environmental conditions such as drought, salinity, temperature extremes, heavy metals toxicity, etc. as well as numerous pathogens. Along with stress-responsive genes, plant microRNAs (miRNAs) play a crucial role in fundamental processes such as growth, development and maintenance of genome integrity in response to abiotic and biotic stresses. MicroRNAs are small 22-24 nt, non-coding regulatory RNAs involved in sequence-specific complex regulatory mechanisms of gene silencing in plants. Role of miRNAs has been implicated in the regulation of plant resistance to abiotic stresses as well as immunity against pathogens. During environmental or biotic stress, defense responses are mediated by changes in both genes and miRNAs expression levels which in turn are involved in the regulation of stress response and resistance in plants. Recent evidences suggest that high-throughput sequencing technologies have significantly contributed towards the identification and functional characterization of numerous miRNAs in plants. It has also been recently reported that primary miRNA transcripts (pri-miRNAs) code for regulatory peptides, roles of some of which have been implicated in improving agronomic traits such as primary root length and nodulation in legumes. Understanding the complex molecular mechanism regulated by miRNAs during abiotic and biotic stresses can potentially offer new approaches to improve plant growth and productivity. Thus, this review summarizes the recent findings and highlights on the contribution of miRNAs as molecular regulators in abiotic stresses and plant-pathogen interactions.