COP1, an important RING ubiquitin ligase E3, is a molecular switch for light regulation in plant development. As an interacting protein of COP1, CIP8 contains a RING-H2 domain, but its biological function is unclear. Here, the apple MdCIP8 was identified based on its homology with AtCIP8 in Arabidopsis. MdCIP8 was constitutively expressed at different levels in various apple tissues, and the expression level of MdCIP8 was not affected by light and dark conditions. MdCIP8 reversed the short hypocotyl phenotype of the cip8 mutant under light conditions. Furthermore, the yeast two-hybrid experiment showed that MdCIP8 interacted with the RING domain of MdCOP1 through its RING-H2 domain. MdCIP8-OX/cop1-4 exhibited the phenotype of the cop1-4 mutant, indicating that CIP8 acts upstream of COP1. In addition, an apple transient injection experiment showed that MdCIP8 inhibited anthocyanin accumulation in an MdCOP1-dependent pathway. Overall, our findings reveal that CIP8 plays an inhibitory role in the light-regulation responses of plants.

中文翻译：

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苹果 RING-H2 蛋白 MdCIP8 通过与 MdCOP1 相互作用调节花青素积累和下胚轴伸长

COP1 是一种重要的 RING 泛素连接酶 E3，是植物发育中光调节的分子开关。作为 COP1 的相互作用蛋白，CIP8 包含一个 RING-H2 结构域，但其生物学功能尚不清楚。在这里，苹果 MdCIP8 根据其与拟南芥中的 AtCIP8 的同源性进行鉴定。MdCIP8在各种苹果组织中呈不同水平的组成型表达，且MdCIP8的表达水平不受光照和黑暗条件的影响。MdCIP8 在光照条件下逆转了 cip8 突变体的短下胚轴表型。此外，酵母双杂交实验表明 MdCIP8 通过其 RING-H2 结构域与 MdCOP1 的 RING 结构域相互作用。MdCIP8-OX/cop1-4 表现出 cop1-4 突变体的表型，表明 CIP8 作用于 COP1 的上游。此外，一项苹果瞬时注射实验表明，MdCIP8 抑制了 MdCOP1 依赖途径中的花青素积累。总的来说，我们的研究结果表明 CIP8 在植物的光调节反应中起着抑制作用。