The trans-Golgi network (TGN), a key compartment in endomembrane trafficking, participates in both secretion to and endocytosis from the plasma membrane. Consequently, the TGN plays a key role in plant growth and development. Understanding how proteins are sorted for secretion or endocytic recycling at the TGN is critical for elucidating mechanisms of plant development. We previously showed that the protein ECHIDNA is essential for phytohormonal control of hypocotyl bending because it mediates secretion of cell wall components and the auxin influx carrier AUXIN RESISTANT 1 (AUX1) from the TGN. Despite the critical role of ECHIDNA in TGN-mediated trafficking, its mode of action remains unknown in Arabidopsis (Arabidopsis thaliana). We therefore performed a suppressor screen on the ech mutant. Here, we report the identification of TGN-localized TYPHON 1 (TPN1) and TPN2 proteins. A single amino acid change in either TPN protein causes dominant suppression of the ech mutant’s defects in growth and AUX1 secretion, while also restoring wild-type-like ethylene-responsive hypocotyl bending. Importantly, genetic and cell biological evidence shows that TPN1 acts through RAS-ASSOCIATED BINDING H1b (RABH1b), a TGN localized RAB-GTPase. These results provide insights into ECHIDNA-mediated secretory trafficking of cell wall and auxin carriers at the TGN, as well as its role in controlling plant growth.

中文翻译：

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TYPHON 蛋白是反式高尔基体网络分泌途径的 RAB 依赖性介质


反式高尔基体网络 （TGN） 是内膜运输的关键隔室，参与质膜的分泌和内吞作用。因此，TGN 在植物生长和发育中起着关键作用。了解蛋白质如何在 TGN 上分选以进行分泌或内吞循环对于阐明植物发育的机制至关重要。我们之前表明，蛋白质 ECHIDNA 对于植物激素控制下胚轴弯曲至关重要，因为它介导细胞壁成分的分泌和生长素内流载体 AUXIN RESISTANT 1 （AUX1） 来自 TGN。尽管 ECHIDNA 在 TGN 介导的运输中起着关键作用，但其在拟南芥 （Arabidopsis thaliana） 中的作用方式仍然未知。因此，我们对 ech 突变体进行了抑制因子筛选。在这里，我们报告了 TGN 定位的 TYPHON 1 （TPN1） 和 TPN2 蛋白的鉴定。任一 TPN 蛋白中的单个氨基酸变化导致 ech 突变体在生长和 AUX1 分泌缺陷方面的显性抑制，同时还能恢复野生型样乙烯反应性下胚轴弯曲。重要的是，遗传和细胞生物学证据表明，TPN1 通过 RAS 相关结合 H1b （RABH1b） 发挥作用，RABH1b 是一种 TGN 定位的 RAB-GTP 酶。这些结果为 ECHIDNA 介导的 TGN 细胞壁和生长素载体的分泌运输及其在控制植物生长中的作用提供了见解。