Under adverse conditions such as shade or elevated temperatures, cotyledon expansion is reduced and hypocotyl growth is promoted to optimize plant architecture. The mechanisms underlying the repression of cotyledon cell expansion remain unknown. Here, we report that the nuclear abundance of the BES1 transcription factor decreased in the cotyledons and increased in the hypocotyl in Arabidopsis thaliana under shade or warmth. Brassinosteroid levels did not follow the same trend. PIF4 and COP1 increased their nuclear abundance in both organs under shade or warmth. PIF4 directly bound the BES1 promoter to enhance its activity but indirectly reduced BES1 expression. COP1 physically interacted with the BES1 protein, promoting its proteasome degradation in the cotyledons. COP1 had the opposite effect in the hypocotyl, demonstrating organ-specific regulatory networks. Our work indicates that shade or warmth reduces BES1 activity by transcriptional and post-translational regulation to inhibit cotyledon cell expansion.

在阴凉或高温等不利条件下，子叶扩张减少并促进下胚轴生长以优化植物结构。抑制子叶细胞扩张的机制仍然未知。在这里，我们报告了在阴影或温暖条件下，拟南芥子叶中 BES1 转录因子的核丰度降低，而下胚轴中的丰度增加。油菜素内酯水平没有遵循同样的趋势。PIF4 和 COP1 在阴凉或温暖的情况下增加了它们在两个器官中的核丰度。PIF4 直接结合BES1启动子以增强其活性但间接降低BES1表达。COP1 与 BES1 蛋白发生物理相互作用，促进其在子叶中的蛋白酶体降解。COP1 在下胚轴中具有相反的作用，表明器官特异性调节网络。我们的工作表明，阴影或温暖通过转录和翻译后调控降低 BES1 活性，从而抑制子叶细胞扩张。