Abstract: Beyond their central role in photosynthesis and plant productivity, chloroplasts are emerging as key regulators of plant responses and tolerance to abiotic stress. However, the molecular mechanisms linking chloroplastic reactive oxygen species (ROS) metabolism to stress adaptation remain poorly understood. Here, we show that knockout of OsJAZ9, a repressor of jasmonic acid (JA) signaling, enhances JA response and drought tolerance in rice by suppressing cellular ROS accumulation. Time-lapse visualization of subcellular ROS dynamics revealed that stress-induced ROS accumulation was initiated in chloroplasts and subsequently propagated to the cytoplasm. Notably, loss of OsJAZ9 markedly suppressed chloroplastic ROS accumulation, resulting in reduced cellular ROS levels under stress conditions. Consistently, either JA treatment or overexpression of the JA-responsive chloroplastic ROS scavenger OsFeSOD3 was sufficient to attenuate chloroplastic ROS accumulation and enhance drought tolerance in rice. Furthermore, two-year agronomic field analyses showed that osjaz9 knockout rice exhibited improved grain yield, particularly under drought stress conditions. Together, our findings identify chloroplast-derived ROS dynamics as a pivotal molecular link between JA signaling and rice stress tolerance and highlight OsJAZ9 as a promising molecular target for developing high-yielding, stress-tolerant rice cultivars

Key words: jasmonic acid, OsJAZ9, abiotic stress, reactive oxygen species, chloroplast, rice