Role of microRNAs in biotic and abiotic stress responses in crop plants.

MicroRNAs (miRNAs) are small non-coding endogenous RNAs (18-24 nucleotides) which regulate gene expression at posttranscriptional level either by degrading the target mRNA (plants) or by blocking the protein translation through binding with 3' UTR of the target mRNA (animals). Though miRNAs are known to play key roles in animal development, miRNAs that are involved in plant developmental timing, cell proliferation, and several other physiological functions need to be investigated. In addition, plant miRNAs have been shown to be involved in various biotic (bacterial and viral pathogenesis) and abiotic stress responses such as oxidative, mineral nutrient deficiency, drought, salinity, temperature, cold (chilling), and other abiotic stress. miRNA expression profiling reveals that miRNAs which are involved in the progression of plant growth and development are differentially expressed during abiotic stress responses. The high-throughout techniques can provide genome-wide identification of stress-associated miRNAs under various abiotic stresses in plants. Various web-based and non-web-based computational tools facilitate in the identification and characterization of biotic/abiotic stress associated miRNAs and their target genes. In the future, miRNA-mediated RNA interference (RNAi) approach might help in developing transgenic crop plants for better crop improvement by conferring resistance against biotic (pathogens) as well as abiotic stress responses.