Regulatory roles of small RNAs in plant growth, breeding, and stress adaptation

Biotic and abiotic stresses are major constraints that severely affect physiological metabolite activities via gene expression at the transcriptional and post-transcriptional levels. Small RNA (sRNA), such as miRNA and siRNA, has emerged as one of the effective alternatives to genetic transformation. sRNA inhibits the transcript level, suppressing transcriptional gene silencing or activating gene-specific mRNA degradation. This technology has been extensively playing a role in combating biotic and abiotic stresses in crops to obtain desirable traits of sRNA. Adopting sRNA techniques and their gene silencing in biotic and abiotic stress responses in crops is well documented. Results have demonstrated that sRNA has been used to develop crop development, growth, and productivity by regulating the gene involved in shoot apical meristem, leaf development, root development, and seed size. The nutritional value and edibility of crops have been mediated by sRNA by enhancing the crops with antioxidants, vitamins, fiber, minerals, shelf life, and seedless fruit. In biotic and abiotic stresses, miRNA as nanoparticles and CRISPR cas9 application provides an effective tool for using sRNA to silence target genes for regulating biotic stress (virus, bacterial, and fungi) and abiotic stress (drought, salinity, heat, and cold). This review highlights the regulatory roles of sRNA and its application for crop improvement where miRNA, TAS3 ta-siRNA, siRNA and their targets can be adopted for crop growth and development.