DREB1C from Medicago truncatula enhances freezing tolerance in transgenic M. truncatula and China Rose (Rosa chinensis Jacq.)

We isolated a DREB orthologue, MtDREB1C, from Medicago truncatula. Its deduced protein contains an AP2 domain of 57 amino acids. Yeast one-hybrid assay revealed that MtDREB1C specifically bound to the dehydration-responsive element (DRE) and activated the expression of HIS3 and LacZ reporter genes. In a transcriptional activation assay, coexpression of the MtDREB1C cDNA resulted in much higher (21.2 times) transactivation of the LacZ reporter gene than experiments performed without MtDREB1C. Transformation of Medicago revealed that overexpression of MtDREB1C suppressed shoot growth, and enhanced the freezing tolerance of M. truncatula. The MtDREB1C gene was transformed into China Rose (Rosa chinensis Jacq.) driven by Arabidopsis rd29A promoter. Southern-blot analysis showed that the target gene was integrated into the genome of a surviving transgenic rose plant. Northern-blot analysis illustrated that robust expression of MtDREB1C was only activated under stress conditions, and the expressed MtDREB1C mRNA reached maximum accumulation 10 h following freezing treatment. The performance of the transgenic line under freezing stress was superior to untransformed controls. This transgenic plant continued to grow, flowered under unstressed conditions, and was phenotypically normal. These facts indicate that the MtDREB1C gene, isolated from Medicago truncatula and driven by the Arabidopsis rd29A promoter, enhanced freezing tolerance in transgenic China Rose significantly without any obvious morphological or developmental abnormality.