Chloroplast sunscreening by protein condensates confers high-light tolerance

Sunlight fuels life but generates singlet oxygen (¹O₂), which causes photodamage and triggers signaling and antioxidative defense pathways in chloroplasts where photosynthesis takes place. How cells sense ¹O₂ and instantaneously mount photoprotection remains elusive. Here, we show that a key mediator of ¹O₂ responses, METHYLENE BLUE SENSITIVITY1 (MBS1), is conserved from plants to animals and comprises a zinc-finger (ZnF) domain flanked by intrinsically disordered regions. MBS1 plays a critical role in ¹O₂ sensing through ZnF conformational change and phase transition from liquid-like droplets to lower-dynamic condensates. These chloroplast-associated condensates under high light attenuate light penetration to shield chloroplasts from photodamage. In rice, MBS1-overexpressing lines exhibit enhanced high-light tolerance and yield in 4-year field trials. Our findings uncover a "sunscreening" mechanism via MBS1 condensates that confer chloroplast photoprotection, highlighting its value for improving rice yields in the field under high-light stress exacerbated by climate change.