The Class III peroxidase OsPrx20 is a key regulator of stress response and growth in rice

In plants, reactive oxygen species (ROS) are maintained at strictly low intracellular levels, a prerequisite for their function as signals. Class III peroxidases serve as core regulators of intracellular ROS homeostasis, if environmental stimuli trigger long-term responses causing ROS accumulation. Here, we found a rice Class III peroxidase OsPrx20, which is a target of Ca2+/calmodulin-dependent protein kinase (OsDMI3) and is phosphorylated at its threonine (Thr)-244 site by OsDMI3, thereby positively regulating osmotic stress tolerance while negatively regulating blast resistance in rice. Overexpression of OsPrx20 enhances osmotic stress tolerance through intracellular ROS scavenging and simultaneously promotes panicle enlargement with increased grain size. Conversely, lack of OsPrx20 potentiates immunity against rice blast infection by elevating intracellular ROS levels but results in reduced plant height and smaller panicles. Crucially, abscisic acid (ABA)-dependent phosphorylation of OsPrx20 at Thr-244 by OsDMI3 scavenges intracellular ROS in rice, thereby enhancing osmotic stress tolerance without compromising growth, but at the expense of blast resistance. In short, our study uncovers an essential regulatory mechanism that directly activates OsPrx20 in ABA signaling, highlighting the multi-functionality of OsPrx20 across contrasting physiological processes.