Cold stress limits plant growth, geographical distribution, and crop yield. The MYC-type bHLH transcription factor ICE1 is recognized as the core positive regulator of the cold-stress response. However, how ICE1 protein levels are regulated remains to be further studied. In this study, we observed that a U-box-type E3 ubiquitin ligase, MdPUB23, positively regulated the cold-stress response in apple. The expression of MdPUB23 increased at both the transcriptional and post-translational levels in response to cold stress. Overexpression of MdPUB23 in transgenic apple enhanced sensitivity to cold stress. Further study showed that MdPUB23 directly interacted with MdICE1, promoting the ubiquitination-mediated degradation of the MdICE1 protein through the 26S-proteasome pathway and reducing the MdICE1-improved cold-stress tolerance in apple. Our results reveal that MdPUB23 regulates the cold-stress response by directly mediating the stability of the positive regulator MdICE1. The PUB23–ICE1 ubiquitination module may play a role in maintaining ICE1 protein homeostasis and preventing overreactions from causing damage to plants. The discovery of the ubiquitination regulatory pathway of ICE1 provides insights for the further exploration of plant cold-stress-response mechanisms.

中文翻译：

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Apple U-box 型 E3 泛素连接酶 MdPUB23 通过降解冷应激调节蛋白 MdICE1 降低冷应激耐受性。

冷胁迫限制了植物生长、地理分布和作物产量。MYC 型 bHLH 转录因子 ICE1 被认为是冷应激反应的核心正调节因子。然而，如何调节 ICE1 蛋白水平仍有待进一步研究。在这项研究中，我们观察到 U-box 型 E3 泛素连接酶 MdPUB23 正向调节苹果的冷应激反应。MdPUB23 的表达响应冷应激在转录和翻译后水平均增加。MdPUB23 在转基因苹果中的过表达增强了对冷胁迫的敏感性。进一步的研究表明，MdPUB23直接与MdICE1相互作用，通过26S-蛋白酶体途径促进泛素化介导的MdICE1蛋白降解，降低了MdICE1提高的苹果对冷胁迫的耐受性。我们的研究结果表明，MdPUB23 通过直接调节正调节因子 MdICE1 的稳定性来调节冷应激反应。PUB23–ICE1 泛素化模块可能在维持 ICE1 蛋白稳态和防止过度反应对植物造成损害方面发挥作用。ICE1泛素化调控通路的发现为进一步探索植物冷胁迫响应机制提供了启示。