GhDREB1 enhances abiotic stress tolerance, delays GA-mediated development and represses cytokinin signalling in transgenic Arabidopsis

Plants vary significantly in their ability to tolerate low temperatures. The CBF/DREB1 cold response pathway has been identified in many plant species and plays a pivotal role in low temperature tolerance. Here, we show that GhDREB1 is a functional homologue and elevates the freezing, salt and osmotic stress tolerance of transgenic Arabidopsis. The constitutive expression of GhDREB1 in Arabidopsis caused dwarfism and late flowering phenotypes, which could be rescued by exogenous application of GA(3). Endogenous bioactive GA contents were significantly lower in GhDREB1 overexpressing Arabidopsis than in wild-type plants. RT-PCR analyses revealed that the transcript levels of the GA synthase genes were higher in transgenics than in wild-type plants, whereas the GA deactivating genes were lower. Flowering related genes in different regulatory pathways were also affected by GhDREB1, which may account for the flowering delay phenotype. Moreover, the GhDREB1 overexpressing Arabidopsis exhibited decreased sensitivity to cytokinin (CK) which is associated with repression of expression of type-B and type-A ARRs, two key components in the CK-signalling pathway.