Contribution of plant miRNAome studies towards understanding heavy metal stress responses: Current Status and Future Perspectives

Abstract Heavy metal toxicity has been identified as a major issue of global concern. Presence of excessive amount of heavy metals (HMs) and metalloids in agricultural soil adversely affects plant growth and productivity. MicroRNAs (miRNAs) are evolutionarily conserved set of tiny (20-24 nucleotides), non-coding RNA molecules that regulate gene expression at post- transcriptional level. Stress induced miRNAs confer tolerance against heavy metals by targeting the negative regulators of stress tolerance, while their downregulation lead to higher accumulation of positive regulators. Advancement in next generation sequencing technology has made microRNAomic a fast, sensitive and reliable technique for identification and characterization of large number of stress responsive miRNAs. Development of user-friendly bioinformatics software enable researchers to precisely identify the target genes of HMs responsive miRNAs which are found to be associated with diverse biological processes including plant growth and development, redox homeostasis, hormone signaling, HMs transport and detoxification pathways. Present review highlights contributions of sRNA transcriptomic studies over a 15-year period (2006 to 2020) towards understanding the miRNA-gene modules to comprehend the complex mechanisms of HMs stress responses in plant. Moreover, challenges and future prospects are discussed in detail to get new insights into the different strategies of HMs detoxification and tolerance mechanisms in plants.