Light and the circadian clock are two essential external and internal cues affecting seedling development. COLD-REGULATED GENE27 (COR27), which is regulated by cold temperatures and light signals, functions as a key regulator of the circadian clock. Here, we report that COR27 acts as a negative regulator of light signaling. COR27 physically interacts with the CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1)–SUPPRESSOR OF PHYTOCHROME A1 (SPA1) E3 ubiquitin ligase complex and undergoes COP1-mediated degradation via the 26S proteasome system in the dark. cor27 mutant seedlings exhibit shorter hypocotyls, while transgenic lines overexpressing COR27 show elongated hypocotyls in the light. In addition, light induces the accumulation of COR27. On one hand, accumulated COR27 interacts with ELONGATED HYPOCOTYL5 (HY5) to repress HY5 DNA binding activity. On the other hand, COR27 associates with the chromatin at the PHYTOCHROME INTERACTING FACTOR4 (PIF4) promoter region and upregulates PIF4 expression in a circadian clock–dependent manner. Together, our findings reveal a mechanistic framework whereby COR27 represses photomorphogenesis in the light and provide insights toward how light and the circadian clock synergistically control hypocotyl growth.

光和生物钟是影响幼苗发育的两个重要的外部和内部线索。冷调节基因 27 (COR27) 受低温和光信号调节，是生物钟的关键调节器。在这里，我们报告 COR27 充当光信号的负调节因子。COR27 与组成型光形态发生蛋白 1 (COP1)-光敏色素 A1 (SPA1) E3 泛素连接酶复合物发生物理相互作用，并在黑暗中通过 26S 蛋白酶体系统经历 COP1 介导的降解。cor27突变体幼苗表现出较短的下胚轴，而转基因株系过度表达COR27在光下显示拉长的下胚轴。此外，光还会诱导COR27的积累。一方面，积累的 COR27 与 ELONGATED HYPOCOTYL5 (HY5) 相互作用，抑制 HY5 DNA 结合活性。另一方面，COR27 与PHYTOCHROME INTERACTING FACTOR4 ( PIF4 ) 启动子区域的染色质结合，并以昼夜节律时钟依赖性方式上调PIF4表达。总之，我们的研究结果揭示了 COR27 抑制光形态发生的机制框架，并为光和生物钟如何协同控制下胚轴生长提供了见解。