The fruit softening directly impacts its storage life, transportability, and customer acceptance. Auxin plays a key role during fruit ripening, but the underlying mechanisms of how auxin regulates fruit softening remain unclear. In this study, we investigated the regulatory roles of auxin on berry cell wall degradation during grape (Vitis vinifera L.) softening. During grape berry development, berry firmness and auxin content are both firstly increasing and then decreasing, and peaks occur at 4-6 WAFB (weeks after full blooming). Exogenous NAA (α-naphthalene acetic acid, a synthetic auxin) treatment inhibits berry softening by delaying propectin, cellulose and hemicellulose degradation, which maintains cell wall integrity in the grape flesh. Weighted gene co-expression network analysis (WGCNA) shows that VvLBD13 correlated with VvARF19 could be a key gene in this delaying of berry softening, which involved in auxin signal transduction and cell wall degradation metabolism. Over-expression and transient over-expression of VvLBD13 in tomato or in grape berry indicate that VvLBD13 accelerates hemicellulose degradation by binding the promoters of VvXTH10 (the xyloglucan endotransglucosylase/hydrolase 10) and VvEXPLA1 (expansion-like A1), which results in rapid softening after veraison. Collectively, this research furnishes an exhaustive understanding of the auxin- driven regulatory mechanisms of grape berry softening.

中文翻译：

---

VvARF19 抑制 VvLBD13 介导的细胞壁降解以延缓葡萄浆果的软化


水果软化直接影响其储存寿命、可运输性和客户接受度。生长素在果实成熟过程中起着关键作用，但生长素如何调节果实软化的潜在机制仍不清楚。在这项研究中，我们研究了生长素对葡萄 （Vitis vinifera L.） 软化过程中浆果细胞壁降解的调节作用。在葡萄浆果发育过程中，浆果硬度和生长素含量均呈先增后减的趋势，峰值出现在 4-6 WAFB（盛花后数周）。外源性 NAA（α-萘乙酸，一种合成生长素）处理通过延迟果胶、纤维素和半纤维素降解来抑制浆果软化，从而维持葡萄果肉中细胞壁的完整性。加权基因共表达网络分析 （WGCNA） 显示，VvLBD13 与 VvARF19 相关可能是延迟浆果软化的关键基因，参与生长素信号转导和细胞壁降解代谢。VvLBD13 在番茄或葡萄浆果中的过表达和瞬时过表达表明，VvLBD13 通过结合 VvXTH10 （木葡聚糖内转葡萄糖酶/水解酶 10） 和 VvEXPLA1 （扩增样 A1） 的启动子来加速半纤维素降解，从而导致转色后快速软化。总的来说，这项研究提供了对葡萄浆果软化的生长素驱动调节机制的详尽理解。