Activation of a DRE-binding transcription factor from Medicago truncatula by deleting a Ser/Thr-rich region

We isolated a DREB homologue gene, MtDREB2A, from Medicago truncatula. Its deduced protein contains an AP2 domain of 59 amino acids. The expression of MtDREB2A was significantly induced in roots by salt and drought treatments. Using megaprimer PCR, we deleted a Ser/Thr-rich coding region between residues 142 and 190, and transformed MtDREB2A to a constitutive form, namely, MtDREB2a. Yeast one-hybrid assay revealed that both MtDREB2A and MtDREB2a specifically bound to the dehydration-responsive element (DRE) and activated the expression of the reporter genes of HIS3 and LacZ. Analysis of transcription activities of the proteins in yeast indicated that MtDREB2a could activate the expression of reporter gene, whereas MtDREB2A could not. Overexpression of MtDREB2a in transgenic M. truncatula resulted in significant dwarfed seedling. These results suggested that MtDREB2A functioned specially in response to salt and drought stresses in M. truncatula and that deletion of the Ser/Thr-rich region between residues 142 and 190 activated the transcriptional activation ability of MtDREB2A.