OsbZIP33 is an ABA-Dependent Enhancer of Drought Tolerance in Rice

The grain yield of crops has been seriously decreased by abiotic stresses all over the world. Identification of crop stress-resistant genes used in molecular breeding is particularly urgent at this time. Here, we characterized the function of a rice (Oryza sativa L.) basic leucine zipper (bZIP) transcription factor, OsbZIP33, under drought stress. Expression of OsbZIP33 was dramatically induced under drought, high salinity, H2O2 and high temperature stresses. Transactivation assays demonstrated that OsbZIP33 had transactivation activity. At both the seedling and five-leaf stages, transgenic rice plants over-expressing OsbZIP33 exhibited significantly improved drought resistance, which was positively correlated with the observed expression levels of OsbZIP33. Representative downstream drought-inducible genes showed significantly higher expression levels in transgenic rice plants than in wild-type plants under drought conditions. OsbZIP33 was shown to be induced by exogenous abscisic acid (ABA) treatment. Overexpression of OsbZIP33 made transgenic plants more sensitive to ABA than wild-type plants. Expression profiles of marker genes in ABA signaling indicated that OsbZIP33 enhanced drought tolerance in rice through ABA-dependent signal transduction pathway. Overall, our findings suggest that OsbZIP33 positively regulates drought resistance in rice. Nevertheless, given the dramatically enhanced drought resistance of rice overexpressing OsbZIP33, further analysis of OsbZIP33 may greatly improve the stress resistance of crops.