Overexpression of OsRbohH Enhances Heat and Drought Tolerance through ROS Homeostasis and ABA Mediated Pathways in Rice (Oryza sativa L.)

Respiratory burst oxidase homologs (Rbohs) are the primary producers of reactive oxygen species (ROS), which have been demonstrated to play critical roles in plant responses to abiotic stress. Here, we explored the function of <i>OsRbohH</i> in heat and drought stress tolerance by generating overexpression lines (<i>OsRbohH</i>-OE). <i>OsRbohH</i> was highly induced by various abiotic stress and hormone treatments. Compared to wild-type (WT) controls, <i>OsRbohH</i>-OE plants exhibited enhanced tolerance to heat and drought, as determined by survival rate analyses and total chlorophyll content. Histochemical staining revealed that <i>OsRbohH</i>-OE accumulated less ROS. This is consistent with the observed increase in catalase (CAT) and peroxidase (POD) activities, as well as a reduced electrolyte leakage rate and malondialdehyde (MDA) content. Moreover, <i>OsRbohH</i>-OE exhibited enhanced sensitivity to exogenous abscisic acid (ABA), accompanied by altered expression levels of ABA synthesis and catabolic genes. Further analysis indicated that transgenic lines had lower transcripts of ABA signaling-related genes (<i>OsDREB2A</i>, <i>OsLEA3</i>, <i>OsbZIP66,</i> and <i>OsbZIP72</i>) under heat but higher levels under drought than WT. In conclusion, these results suggest that <i>OsRbohH</i> is a positive regulator of heat and drought tolerance in rice, which is probably performed through OsRbohH-mediated ROS homeostasis and ABA signaling.