The orange protein regulates the minor antenna protein CP24 via an oxidative stress-dependent structural switch.

Abiotic stress significantly affects plant photosynthetic efficiency, leading to a global reduction in agricultural yields. The Orange (Or) protein plays a crucial role in regulating carotenoid homeostasis and enhancing plant adaptation to abiotic stress. In this study, we found that the sweetpotato Or protein (IbOr) physically interacts with the minor antenna protein IbCP24 in the chloroplast and promotes its degradation. When treated with H2O2, transgenic plants overexpressing IbOr showed significantly lower CP24 protein levels than the Or knockout mutant plant. Additionally, IbOr structure was altered by changes in redox potential, forming high-molecular-weight oligomers via disulfide bonds upon H2O2 treatment. CP24 knockout plants showed significantly reduced PSII photochemical efficiency. Based on these findings, we propose that IbOr regulates CP24 protein levels through redox-dependent changes in its structure in response to H2O2 signaling. This mechanism may function to fine-tune photosynthesis and balance light harvesting with downstream photosynthetic processes, thereby maintaining optimal redox conditions in the chloroplast. Our findings reveal a novel mechanism by which the minor antenna CP24 protein is regulated by disulfide-bond-mediated oligomerization of Or protein in the chloroplast.