Functional diversity of miRNA in plants

MicroRNAs (miRNAs) are endogenous approximate 22 nucleotide small RNAs that play important regulatory roles in animals and plants by targeting mRNAs for cleavage or translational repression. Past few years have witnessed an explosive increase in research reports on plant miRNAs. To date, more than 700 miRNAs have been identified with cloning methods or computational approaches from a variety of plants. Large numbers of miRNA targets were predicted, some of which were validated or confirmed experimentally. In addition to their important functions in organ development such as leaf morphogenesis, floral organ identity and root development, plant miRNAs also function in feedback regulation in small RNA pathway and in directing some siRNAs biogenesis. Moreover, they are involved in various stress responses, such as oxidative, mineral-nutrient, dehydration stress and even mechanical stress. However, the unexpected new data about miRNAs imply that we just make the first step in the small RNA world.