osa-MIR393: a salinity- and alkaline stress-related microRNA gene.

Salinity and alkalinity are the two main environmental factors that limit rice production. Better understanding of the mechanisms responsible for salinity and alkaline stress tolerance would allow researchers to modify rice to increase its resistance to salinity and alkaline stress. MicroRNAs (miRNAs) are ~21-nucleotide RNAs that are ubiquitous regulators of gene expression in eukaryotic organisms. Some miRNAs acts as an important endogenous regulator in plant responses to abiotic stressors. miR393 is a conservative miRNA family that occurs in a variety of different plants. The two members of the miR393 family found in rice are named osa-MIR393 and osa-MIR393b. We found that the osa-MIR393 expression level changed under salinity and alkaline stress, whereas that of osa-MIR393b did not. Target genes of osa-MIR393 were predicted, and some of these putative targets are abiotic related genes. Furthermore, we generated transgenic rice and Arabidopsis thaliana that over-expressed osa-MIR393, and the phenotype analysis showed that these transgenic plants were more sensitive to salt and alkali treatment compared to wild-type plants. These results illustrate that over-expression of osa-MIR393 can negatively regulate rice salt-alkali stress tolerance.