Isolation and Characterization of a OsRap2.4A Transcription Factor and its Expression in Arabidopsis for Enhancing High Salt and Drought Tolerance

Dehydration responsive element/C-repeat (DRE/CRT) is a cis-acting element involved in the regulation of abiotic stress-responsive gene expression in higher plants. Using a 50-nucleotide bait containing DRE cis-acting element localized on the downstream mini TATA box of glutamate dehydrogenase-like protein (JRC2606) promoter in yeast one-hybrid screening, we have identified two transcription factors belonging to A6 subgroup of DREB subfamily - OsRap2.4A and OsRap2.4B. Expression of OsRap2.4A was induced by drought, high salt and temperature stress conditions, and also by abscisic acid treatment. Binding assay showed that OsRap2.4A bound specifically to DRE sequence in both in vivo and in vitro experiments. Transient expression of OsRap2.4A in protoplasts revealed that OsRap2.4A functioned as a transcriptional activator and upregulated expression of the GUS re-porter gene. Transgenic Arabidopsis plants expressing OsRap2.4A at low level showed no significant growth re-tardation under normal condition, whereas at high level expression of OsRap2.4A caused an obvious retardation. Expression of OsRap2.4A showed the tolerance against drought and salt stresses in comparison with control. These results suggested that OsRap2.4A gene may be involved in a new regulatory pathway in plant responses to abiotic stresses and it is potentially useful for the transformation into crop plants to improve tolerance against drought and high salt stresses.