Overexpressing heat-shock protein OsHSP50.2 improves drought tolerance in rice

OsHSP50.2, an HSP90 family gene up-regulated by heat and osmotic stress treatments, positively regulates drought stress tolerance probably by modulating ROS homeostasis and osmotic adjustment in rice. Heat-shock proteins (HSPs) serve as molecular chaperones for a variety of client proteins in abiotic stress response and play pivotal roles in protecting plants against stress, but the molecular mechanism remains largely unknown. Here, we report an HSP90 family gene, OsHSP50.2, which acts as a positive regulator in drought stress tolerance in rice (Oryza sativa). OsHSP50.2 was ubiquitously expressed and its transcript level was up-regulated by heat and osmotic stress treatments. Overexpression of OsHSP50.2 in rice reduced water loss and enhanced the transgenic plant tolerance to drought and osmotic stresses. The OsHSP50.2-overexpressing plants exhibited significantly lower levels of electrolyte leakage and malondialdehyde (MDA) and less decrease of chlorophyll than wild-type plants under drought stress. Moreover, the OsHSP50.2-overexpressing plants had significantly higher SOD activity under drought stress compared with the wild type. These results imply that OsHSP50.2 positively regulates drought stress tolerance in rice, probably through the modulation of reactive oxygen species (ROS) homeostasis. Additionally, the OsHSP50.2-overexpressing plants accumulated significantly higher content of proline than the wild type under drought stress, which contributes to the improved protection ability from drought stress damage via osmotic adjustment. Our findings reveal that OsHSP50.2 plays a crucial role in drought stress response, and it may possess high potential usefulness in drought tolerance improvement of rice.