Small ubiquitin-like modifier (SUMO) post-translational modification (SUMOylation) plays essential roles in regulating various biological processes; however, its function and regulation in the plant light signaling pathway are largely unknown. SEUSS (SEU) is a transcriptional co-regulator that integrates light and temperature signaling pathways, thereby regulating plant growth and development in Arabidopsis thaliana. Here, we show that SEU is a substrate of SUMO1, and that substitution of four conserved lysine residues disrupts the SUMOylation of SEU, impairs its function in photo- and thermomorphogenesis, and enhances its interaction with PHYTOCHROME-INTERACTING FACTOR 4 transcription factors. Furthermore, the SUMO E3 ligase SIZ1 interacts with SEU and regulates its SUMOylation. Moreover, SEU directly interacts with phytochrome B photoreceptors, and the SUMOylation and stability of SEU are activated by light. Our study reveals a novel post-translational modification mechanism of SEU in which light regulates plant growth and development through SUMOylation-mediated protein stability.

小泛素样修饰剂 (SUMO) 翻译后修饰 (SUMOylation) 在调节各种生物过程中起着至关重要的作用；然而，其在植物光信号通路中的功能和调控在很大程度上是未知的。SEUSS (SEU) 是一种转录共调节剂，可整合光和温度信号通路，从而调节拟南芥植物的生长发育. 在这里，我们表明 SEU 是 SUMO1 的底物，替换四个保守的赖氨酸残基会破坏 SEU 的 SUMO 化，削弱其在光和热形态发生中的功能，并增强其与光致变色相互作用因子 4 转录因子的相互作用。此外，SUMO E3 连接酶 SIZ1 与 SEU 相互作用并调节其 SUMO 化。此外，SEU 直接与光敏色素 B 光感受器相互作用，SEU 的 SUMO 化和稳定性被光激活。我们的研究揭示了一种新的 SEU 翻译后修饰机制，其中光通过 SUMOylation 介导的蛋白质稳定性来调节植物的生长和发育。