Although DELLA protein destabilization mediated by post-translational modifications is essential for gibberellin (GA) signal transduction and GA-regulated anthocyanin biosynthesis, the related mechanisms remain largely unknown. In this study, we report the ubiquitination and phosphorylation of an apple DELLA protein MdRGL2a in response to GA signaling and its regulatory role in anthocyanin biosynthesis. MdRGL2a could interact with MdWRKY75 to enhance the MdWRKY75-activated transcription of anthocyanin activator MdMYB1 and interfere with the interaction between anthocyanin repressor MdMYB308 and MdbHLH3 or MdbHLH33, thereby promoting anthocyanin accumulation. A protein kinase MdCIPK20 was found to phosphorylate and protect MdRGL2a from degradation, and it was essential for MdRGL2a-promoting anthocyanin accumulation. However, MdRGL2a and MdCIPK20 were ubiquitinated and degraded by E3 ubiquitin ligases MdSINA1 and MdSINA2, respectively, both of which were activated in the presence of GA. Our results display the integration of SINA1/2 with CIPK20 to dynamically regulate GA signaling and will be helpful toward understanding the mechanism of GA signal transduction and GA-inhibited anthocyanin biosynthesis. The discovery of extensive interactions between DELLA and SINA and CIPK proteins in apple will provide reference for the study of ubiquitination and phosphorylation of DELLA proteins in other species.

中文翻译：

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E3 泛素连接酶 SINA1 和 SINA2 与蛋白激酶 CIPK20 整合，调节 RGL2a 的稳定性，RGL2a 是花青素生物合成的正调节因子。

尽管翻译后修饰介导的 DELLA 蛋白去稳定对于赤霉素 (GA) 信号转导和 GA 调节的花青素生物合成至关重要，但相关机制仍然很大程度上未知。在这项研究中，我们报道了苹果 DELLA 蛋白 MdRGL2a 响应 GA 信号的泛素化和磷酸化及其在花青素生物合成中的调节作用。MdRGL2a可以与MdWRKY75相互作用，增强MdWRKY75激活的花青素激活剂MdMYB1的转录，并干扰花青素抑制子MdMYB308与MdbHLH3或MdbHLH33之间的相互作用，从而促进花青素积累。人们发现蛋白激酶 MdCIPK20 可以磷酸化并保护 MdRGL2a 免遭降解，并且它对于 MdRGL2a 促进花青素积累至关重要。然而，MdRGL2a 和 MdCIPK20 分别被 E3 泛素连接酶 MdSINA1 和 MdSINA2 泛素化和降解，这两种酶都在 GA 存在下被激活。我们的结果显示SINA1/2与CIPK20的整合能够动态调节GA信号传导，将有助于理解GA信号转导和GA抑制花青素生物合成的机制。苹果中DELLA与SINA和CIPK蛋白广泛相互作用的发现将为其他物种中DELLA蛋白泛素化和磷酸化的研究提供参考。我们的结果显示SINA1/2与CIPK20的整合能够动态调节GA信号传导，将有助于理解GA信号转导和GA抑制花青素生物合成的机制。苹果中DELLA与SINA和CIPK蛋白广泛相互作用的发现将为其他物种中DELLA蛋白泛素化和磷酸化的研究提供参考。我们的结果显示SINA1/2与CIPK20的整合能够动态调节GA信号传导，将有助于理解GA信号转导和GA抑制花青素生物合成的机制。苹果中DELLA与SINA和CIPK蛋白广泛相互作用的发现将为其他物种中DELLA蛋白泛素化和磷酸化的研究提供参考。