<scp>OsFeSOD3</scp> Functions as an Enzymatic Component of the <scp>PEP</scp> Complex, Bifunctionally Regulating Chloroplastic <scp>ROS</scp> Metabolism and Chloroplast Biogenesis in Rice

Chloroplasts are essential organelles responsible for photosynthesis, providing energy and metabolic intermediates required for plant growth and productivity. Chloroplast development is highly sensitive to environmental stresses such as drought, and this sensitivity is closely associated with growth inhibition and yield reduction under stress conditions. However, the molecular mechanisms governing this process remain largely elusive. In this study, we demonstrate that chloroplastic ROS metabolism plays a pivotal role in modulating chloroplast development in response to abiotic stress, and we identify OsFeSOD3, which encodes a chloroplast-localised iron superoxide dismutase, as a key regulator of this process. Time-lapse visualisation of cellular ROS dynamics and characterisation of OsFeSOD3-overexpressing rice showed that OsFeSOD3-mediated chloroplastic ROS metabolism is tightly associated with cytoplasmic ROS accumulation under stress conditions, and that overexpression of OsFeSOD3 is sufficient to enhance rice stress tolerance by reducing cellular ROS accumulation. Furthermore, agronomic trait analyses over 2 years of cultivation revealed that OsFeSOD3-overexpressing rice exhibits a 33%-42% increase in grain yield under drought conditions compared with wild-type plants, highlighting OsFeSOD3 as a promising genetic target for developing stress-tolerant, high-yielding crops. Moreover, phenotypic and molecular characterisation of OsFeSOD3 knock-out mutants indicates that OsFeSOD3 functions as a PEP-complex component regulating chloroplast biogenesis in rice, a role further supported by its direct interaction with other PEP-complex proteins. Taken together, our findings suggest that OsFeSOD3 serves as a bifunctional regulator that coordinates chloroplastic ROS metabolism and chloroplast biogenesis in rice.