背景回顾：Under adverse conditions such as shade or elevated temperatures, cotyledon expansion is reduced and hypocotyl growth is promoted to optimize plant architecture. 

提出问题：The mechanisms underlying the repression of cotyledon cell expansion remain unknown.

结果1-BES1：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. 

结果1-PIF4：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. 

结果2-COP1：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. 

结论：Our work indicates that shade or warmth reduces BES1 activity by transcriptional and post-translational regulation to inhibit cotyledon cell expansion.

 摘 要 

在荫蔽或高温等不利条件下，子叶扩张减少，下胚轴伸长加速，从而达到最优的植物结构。但是，抑制子叶细胞扩张的分子机制尚不清楚。本文中，作者发现在荫蔽或温暖条件下，拟南芥BES1转录因子在子叶中的核丰度降低，但是在下胚轴中的核丰富度增加。油菜素内酯的水平并没有类似的趋势。在荫蔽或温暖条件下，子叶和下胚轴中PIF4和COP1的核丰度都有所增加。PIF4能够直接结合BES1基因的启动子，以增强其转录活性，但会间接降低BES1的表达。COP1与BES1蛋白发生物理互作，促进其在子叶中经由蛋白酶体途径而降解。但是，COP1在下胚轴中具有与子叶中完全相反的作用，说明了器官特异性的调控网络。本文的研究结果表明，荫蔽或温暖环境会通过转录和翻译后调节降低BES1活性，从而抑制子叶细胞的扩张。

 Jorge J. Casal