A nuclear-localized histone-gene binding protein from rice (OsHBP1b) functions in salinity and drought stress tolerance by maintaining chlorophyll content and improving the antioxidant machinery

Plants have evolved a number of molecular strategies and regulatory mechanisms to cope with abiotic stresses. Among the various key factors/regulators, transcription factors (TFs) play critical role(s) towards regulating the gene expression patterns in response to stress conditions. Altering the expression of the key TFs can greatly influence plant stress tolerance. OsHBP1b (accession no. KM096571) is one such TF belonging to bZIP family, localized within the Saltol QTL, whose expression is induced upon salinity treatment in the rice seedlings. qRT-PCR based expression studies for OsHBP1b in seedlings of contrasting genotypes of rice showed its differential regulation in response to salinity stress. A GFP based in vivo study showed that the OsHBP1b protein is nuclear localized and possesses the trans-activation activity. As compared to the WT tobacco plants, the transgenic plants ectopically expressing OsHBP1b showed better survival and favourable osmotic parameters (such as germination and survival rate, membrane stability, K+/Na+ ratio, lipid peroxidation, electrolyte leakage and proline contents) under salinity and drought stress. Under salinity conditions, the transgenic plants accumulated lower levels of reactive oxygen species as compared to the WT. It was also accompanied by higher activities of antioxidant enzymes (such as ascorbate peroxidase and superoxide dismutase), thereby demonstrating that transgenic plants are physiologically better adapted towards the oxidative damage. Taken together, our findings suggest that OsHBP1b contributes to abiotic stress tolerance through multiple physiological pathways and thus, may serve as a useful 'candidate gene' for improving multiple stress tolerance in crop plants.