Proanthocyanidins (PAs) are an important group of flavonoids that contribute to astringency, color, and flavor in grape (Vitis vinifera) and wines. They also play a crucial role in enhancing plant resistance to various stresses. However, the underlying regulatory mechanism governing PAs biosynthesis, particularly in relation to conferring resistance to powdery mildew, has not been extensively explored. This study focused on identifying a key player in PAs biosynthesis, namely the plant U-box (PUB) E3 ubiquitin ligase VvPUB26. We discovered that overexpression of VvPUB26 in grape leads to a significant increase in PAs content, whereas interfering with VvPUB26 has the opposite effect. Additionally, our findings demonstrated that overexpression of VvPUB26 in transgenic grapevines enhances defense against powdery mildew, while interfering with VvPUB26 results in increased susceptibility to the pathogen. Interestingly, we observed that VvPUB26 interacts with the WRKY transcription factor VvWRKY24, thereby facilitating ubiquitination and degradation processes. Through RNA-Seq analysis, we found that VvWRKY24 primarily participates in secondary metabolites biosynthesis, metabolic pathways, and plant-pathogen interaction. Notably, VvWRKY24 directly interacts with the promoters of dihydroflavonol-4-reductase (DFR) and leucoanthocyanidin reductase (LAR) to inhibit PAs biosynthesis. Meanwhile, VvWRKY24 also influences the expression of MYB transcription factor genes related to PAs synthesis. In conclusion, our results unveil a regulatory module involving VvPUB26-VvWRKY24-VvDFR/VvLAR that plays a fundamental role in governing PAs biosynthesis in grapevines. These findings enhance our understanding of the relationship between PAs biosynthesis and defense mechanisms against powdery mildew.

中文翻译：

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葡萄中泛素连接酶VvPUB26促进原花青素合成和抗白粉病

原花青素 (PA) 是一组重要的黄酮类化合物，有助于提高葡萄 (Vitis vinifera) 和葡萄酒的涩味、颜色和风味。它们在增强植物对各种胁迫的抵抗力方面也发挥着至关重要的作用。然而，PAs生物合成的潜在调控机制，特别是与白粉病抗性相关的机制，尚未得到广泛探索。本研究的重点是确定 PA 生物合成中的关键参与者，即植物 U-box (PUB) E3 泛素连接酶 VvPUB26。我们发现，在葡萄中过度表达VvPUB26会导致PAs含量显着增加，而干扰VvPUB26则会产生相反的效果。此外，我们的研究结果表明，转基因葡萄藤中 VvPUB26 的过度表达可增强对白粉病的防御，而干扰 VvPUB26 会导致对病原体的易感性增加。有趣的是，我们观察到 VvPUB26 与 WRKY 转录因子 VvWRKY24 相互作用，从而促进泛素化和降解过程。通过RNA-Seq分析，我们发现VvWRKY24主要参与次生代谢物的生物合成、代谢途径以及植物与病原体的相互作用。值得注意的是，VvWRKY24 直接与二氢黄酮醇-4-还原酶 (DFR) 和无色花青素还原酶 (LAR) 的启动子相互作用，抑制 PA 生物合成。同时，VvWRKY24还影响与PA合成相关的MYB转录因子基因的表达。总之，我们的结果揭示了一个涉及 VvPUB26-VvWRKY24-VvDFR/VvLAR 的调控模块，该模块在控制葡萄藤 PA 生物合成中发挥着基础作用。这些发现增强了我们对 PA 生物合成与白粉病防御机制之间关系的理解。