Small RNAs (sRNAs) are 18-30 nt non-coding regulatory elements found in diverse organisms,which were initially identified as small double-stranded RNAs in Caenorhabditis elegans.With the development of new and improved technologies,sRNAs have also been identified and characterized in plant systems.Among them,micro RNAs (miRNAs) and small interfering RNAs (siRNAs) are found to be very important riboregulators in plants.Various types of sRNAs differ in their mode of biogenesis and in their function of gene regulation.sRNAs are involved in gene regulation at both transcriptional and post-transcriptional levels.They are known to regulate growth and development of plants.Furthermore,sRNAs especially plant miRNAs have been found to be involved in various stress responses,such as oxidative,mineral nutrient deficiency,dehydration,and even mechanical stimulus.Therefore,in the present review,we focus on the current understanding of biogenesis and regulatory mechanisms of plant sRNAs and their responses to various abiotic stresses.

MicroRNAs (miRNAs) usually contain 19-24 nucleotides and have been identified as important eukaryotic gene regulators.Applications of various computational approaches have simplified the task by predicting miRNAs from available sequence data sources.In this study,we identified a conserved miR414 from a computational analysis of EST sequence data available from Stevia rebaudiana.In addition,we also identified six conserved miRNAs namely miR169,miR319,miR414,miR164,miR167 and miR398 using stem-loop RT-PCR analysis.Hence,miR414 was commonly identified using both methods.The expression analysis of these miRNAs documented their roles in growth and development of Stevia.Furthermore,the detected miRNAs were found to target genes involved in plant growth,development,metabolism and signal transduction.This is the first study reporting these conserved miRNAs and their expression in Stevia.