Allelic variation in UVR8 modulates thermotolerance-yield tradeoffs in plants.
Industrial activities have driven stratospheric ozone depletion, increasing surface UV-B radiation while exacerbating global warming. These changes limit crop productivity, alter species distributions, and disrupt plant metabolic processes, but the mechanisms linking energy signaling to heat-stress responses remain unclear. Here, we identify the photoreceptor UV RESISTANCE LOCUS 8b (OsUVR8b) as a substrate of SNF1-related protein kinase 1 (SnRK1) in rice and reveal a natural variation at its SnRK1-mediated phosphorylation site (Ser177) that is correlated with adaptation to tropical climates. The thermotolerant OsUVR8bAla177 accessions show geographic enrichment in low-latitude regions with elevated temperatures. Functional validation through prime editing demonstrated that a Ser177-to-Ala177 substitution enhances heat tolerance, whereas the reverse edit compromises it. Mechanistically, OsUVR8bSer177 exhibits reduced stability and an impaired capacity for scavenging reactive oxygen species under heat stress. The regulatory function of the OsUVR8b Ser177 phosphorylation site, a molecular switch that governs UVR8 stability and thermotolerance, can be functionally re-established across rice, Arabidopsis, tobacco, and soybean, indicating its preservation during domestication. Notably, OsUVR8bSer177 maintains higher fertility and yield under non-stress conditions, indicating a tradeoff between heat adaptation and productivity. Our findings thus establish this switch as a key regulator of the yield-resilience balance and a promising target for breeding of climate-resilient crops.