Cellular sunscreen helps boost rice yields

Plants weave sunbeams into complex carbohydrates via photosynthesis, but excess sunlight can also fry the photosynthetic machinery used to do that. Scientists have now discovered that a shape-shifting protein protects against molecular sunburns by slathering itself on the chloroplasts where photosynthesis takes place (Cell 2026, DOI: 10.1016/j.cell.2026.05.042). Field trials showed that modifying rice to overexpress the protein improves yields in areas with high solar radiation.

When chlorophyll molecules absorb more light than they can use for photosynthesis, they release a reactive oxygen species called singlet oxygen (¹O₂) that ravages the plant’s core photosynthetic engine, photosystem II. “Sustained intense light leads to massive ¹O₂ accumulation inside plant chloroplasts, impairs photosynthesis and reduces crop yields,” Jiayang Li, a plant molecular biologist at the Chinese Academy of Sciences’ Institute of Genetics and Developmental Biology, says in an email.

Plants deploy a brilliant arsenal of biophysical and molecular defenses against this singlet oxygen, including moving around chloroplasts, producing anthocyanin pigments, and blowing off excess absorbed light energy as heat. To do this, Li says, “plants rely on a protein called MBS1 [Methylene Blue Sensitivity 1] to detect ¹O₂ signals.”

Li’s team subjected MBS1 to nuclear magnetic resonance spectroscopy and discovered that its alarm system relies on a C₂H₂ zinc-finger domain, where two cysteine and two histidine amino acids lock a zinc ion (Zn²⁺) firmly in place. Under strong light, ¹O₂ oxidizes the two cysteines to form a disulfide bond between them, making them drop the Zn²⁺ and triggering a structural change. MBS1 then undergoes liquid–liquid phase separation, forming dense protein condensates that coat the chloroplast’s outer envelope like a sunscreen lotion. This coating scatters incoming intense light and cuts down light penetration by 43.9%, thus mitigating light-triggered damage to photosynthesis. All this happens within 8 min of exposure to ¹O₂.

“Conventional photoprotective pathways respond too slowly against sustained high light,” Li says. “No fast protein-derived barrier in chloroplasts has been identified before our work.”

The researchers tagged MBS1 with a fluorescent marker and saw how the tagged proteins cluster into visible granules and aggregate around the chloroplasts when a plant cell is exposed to intense light. After 7 h of intense light exposure, the MBS1 further condensed into a thick, viscous gel reinforcing its photoprotection. MBS1 reverted to its original state once the light exposure was cut off, showing that this transition is reversible.

Next, the team created two transgenic rice lines that overexpressed MBS1 and conducted field trials in different places of China with different levels of solar radiation. In high-radiation Hainan, the transgenic lines exhibited a massive 40.2% and 47.1% increase in grain yield per block compared with wild-type cultivar.

“MBS1 is evolutionarily conserved across plant species,” Li says. “Scientists can introduce this protective trait into other staple crops to secure stable food production in regions with extreme solar radiation.”

Minjung Son, a chemist at Boston University who wasn’t involved in the study, calls it “remarkable” that biomolecular condensates are not just organizing cellular chemistry but “can directly influence how cells interact with light.”

Son thinks overexpression of MBS1 can be used to improve productivity in different crops, as MBS1 appears to be evolutionarily conserved. But she cautions that the actual outcome will depend on factors such as the kind of crop, growing environment, and how light stress interacts with other environmental factors such as heat and drought. “The rice field trials are very promising because they show reproducible yield gains over multiple years and locations, but similar studies will need to be conducted in other major crops before we know how broadly applicable this strategy is,” Son says.