miRNA applications for engineering abiotic stress tolerance in plants

MicroRNAs (miRNAs) are endogenous, tiny RNA molecules that sit at the heart of regulating gene expression in numerous developmental and signaling pathways. Recent investigations have revealed that abiotic stresses encourage non-typical expression patterns of several miRNAs, accordingly proposing miRNAs as potent and novel targets for enhancement plant tolerance against abiotic factors. The stress driven miRNA-response is dependent on types of miRNA, stress, tissues or organs as well as plant genotype. The stress responsive miRNAs act either as negative-regulatory entities by down regulating negative regulators for stress tolerance or as positive-regulatory entities approving amassing of positive regulators. The current scenario on miRNA-based research vastly focus on the identification and target prediction/validation of stress-responsive miRNAs along with their functional expression under stress conditions. It has predominately been accomplished with the advent of high throughput sequencing technologies coupled with online databases and tools. However, there is an urge of epigenomics, functional characterization, and expression-pattern studies to illuminate the communal regulatory pathways by miRNAs that trigger abiotic stress tolerance in major crops. The short tandem target mimic (STTM) and genome editing technologies can be exploited for efficient utilization of miRNAs for traits improvement. Beside the classical pathways, non canonical pathways and novel loci of miRNAs origin and their possible role in abiotic stress response need to be deciphered for their effective utilization. Through this review, we are presenting herein a current understanding about plant miRNAs, their biogenesis and involvement in stress-responses and modulation, various tools and databases used for prediction/identification of plant miRNAs and their targets. A perspective analysis on use of miRNAs as potent targets to engineer abiotic stress tolerance in plants has been presented with emphasis on recent developments, challenges and future perspectives.