背景回顾：The ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) plays a central role in light-induced anthocyanin biosynthesis. 

提出问题：However, the upstream regulatory factors of COP1 remain poorly understood, particularly in horticultural plants. 

主要发现：Here, we identified a MdCOP1-interacting protein, BROAD-COMPLEX, TRAMTRACK AND BRIC A BRAC2 (MdBT2), in apple (Malus domestica). 

结果1-互作：MdBT2 is a BTB protein that directly interacts with and stabilizes MdCOP1 by inhibiting self-ubiquitination. Fluorescence observation and cell fractionation assays showed that MdBT2 increased the abundance of MdCOP1 in the nucleus. 

结果2-功能：Moreover, a series of phenotypic analyses indicated that MdBT2 promoted MdCOP1-mediated ubiquitination and degradation of the MdMYB1 transcription factor, inhibiting the expression of anthocyanin biosynthesis genes and anthocyanin accumulation. 

结论：Overall, our findings reveal a molecular mechanism by which MdBT2 positively regulates MdCOP1, providing insight into MdCOP1-mediated anthocyanin biosynthesis.  

 摘 要 

泛素连接酶COP1在光诱导花色苷生物合成中发挥核心作用。然而，COP1的上游调节因子仍然知之甚少，尤其是在园艺植物中。本文中，作者鉴定到了一个与苹果COP1互作的蛋白，即MdBT2。MdBT2是一个BTB蛋白，能够直接与MdCOP1发生互作，并通过抑制其自身泛素化来稳定MdCOP1。荧光观察和细胞分离实验表明，MdBT2增加了细胞核中MdCOP1的丰度。此外，一系列表型分析表明，MdBT2能够促进MdCOP1介导的MdMYB1转录因子泛素化和降解，抑制花色苷生物合成基因的表达和花色苷的积累。总的来说，本文的研究结果揭示了一个MdBT2正调控MdCOP1的分子机制，为深入理解MdCOP1介导的花色苷生物合成提供了新的视野。

 王小非