Tao Ruiyan, Trivedi Ira, Trimborn Laura, Ponnu Jathish, Tóth Blanka Violetta, Hoecker Ute
Institute for Plant Sciences and Cluster of Excellence on Plant Sciences (CEPLAS), Department of Biology, Biocenter, University of Cologne, Cologne 50674, Germany.
Proc Natl Acad Sci U S A. 2025 May 20;122(20):e2426423122. doi: 10.1073/pnas.2426423122. Epub 2025 May 13.
COP1 is a conserved ubiquitin ligase found in plants and animals. In plants, COP1 acts together with SPA proteins to suppress light signaling in darkness by promoting the degradation of transcription factors involved in photomorphogenesis. Substrates of this ubiquitin ligase share a Valine-Proline (VP) motif that interacts with the WD-repeat domain of COP1 in plants and humans. Here, we have identified the transcription factor TCP3 as a noncanonical substrate of COP1/SPA that lacks a VP motif. The TCP domain of TCP3 directly interacts with the WD-repeat domains of COP1 and SPA1. TCP3 requires the VP-binding cleft of COP1 for protein-protein interaction. We further show that the TCP3 protein is degraded in darkness and preferentially in short day through a COP1-dependent manner, while TCP3 is stabilized by red, far-red, blue light, and long day conditions. COP1/SPA-mediated degradation of TCP3 inhibits anthocyanin accumulation by reducing the expression of anthocyanin biosynthesis genes. COP1/SPA-mediated degradation of TCP3 is also important in regulating flowering time. Taken together, our results have identified a noncanonical substrate of the COP1/SPA ubiquitin ligase, thereby also uncovering TCPs as a transcription factor family that is targeted by COP1/SPA. Since the COP1/SPA-interacting TCP domain is conserved among TCPs, it is possible that other members of the TCP family-having divergent functions including cell fate determination and hormone signaling-are targets of COP1/SPA as well.
COP1是一种在植物和动物中均存在的保守泛素连接酶。在植物中，COP1与SPA蛋白共同作用，通过促进光形态建成相关转录因子的降解，在黑暗中抑制光信号传导。这种泛素连接酶的底物具有一个缬氨酸-脯氨酸（VP）基序，该基序在植物和人类中与COP1的WD重复结构域相互作用。在这里，我们鉴定出转录因子TCP3是COP1/SPA的一种非典型底物，它缺乏VP基序。TCP3的TCP结构域直接与COP1和SPA1的WD重复结构域相互作用。TCP3需要COP1的VP结合裂隙来进行蛋白质-蛋白质相互作用。我们进一步表明，TCP3蛋白在黑暗中，特别是在短日照条件下，通过COP1依赖的方式被降解，而在红光、远红光、蓝光和长日照条件下TCP3则保持稳定。COP1/SPA介导的TCP3降解通过降低花青素生物合成基因的表达来抑制花青素积累。COP1/SPA介导的TCP3降解在调节开花时间方面也很重要。综上所述，我们的研究结果鉴定出了COP1/SPA泛素连接酶的一种非典型底物，从而也揭示了TCPs作为一个被COP1/SPA靶向的转录因子家族。由于在TCPs中与COP1/SPA相互作用的TCP结构域是保守的，因此TCP家族的其他成员——具有包括细胞命运决定和激素信号传导等不同功能——也有可能是COP1/SPA的作用靶点。
