As the major nutritional component in soybean seeds storage proteins are initially synthesized on the endoplasmic reticulum as precursors and subsequently delivered to protein storage vacuoles (PSVs) via the Golgi-mediated pathway where they are converted into mature subunits and accumulated. However, the molecular machinery required for storage protein trafficking in soybean remains largely unknown. In this study, we cloned the sole soybean homolog of OsGPA3 that encodes a plant-unique kelch-repeat regulator of post-Golgi vesicular traffic for rice storage protein sorting. A complementation test showed that GmGPA3 could rescue the rice gpa3 mutant. Biochemical assays verified that GmGPA3 physically interacts with GmRab5 and its guanine exchange factor (GEF) GmVPS9. Expression of GmGPA3 had no obvious effect on the GEF activity of GmVPS9 toward GmRab5a. Notably, knock-down of GmGPA3 disrupted the trafficking of mmRFP-CT10 (an artificial cargo destined for PSVs) in developing soybean cotyledons. We identified two putative GmGPA3 interacting partners (GmGMG3 and GmGMG11) by screening a yeast cDNA library. Overexpression of GmGPA3 or GmGMG3 caused shrunken cotyledon cells. Our overall results suggested that GmGPA3 plays an important role in cell growth and development, in addition to its conserved role in mediating storage protein trafficking in soybean cotyledons.

中文翻译：

---

GmGPA3 参与高尔基体后储存蛋白的运输和大豆子叶中的细胞生长


作为大豆种子中的主要营养成分，储存蛋白最初作为前体在内质网上合成，随后通过高尔基体介导的途径递送至蛋白质储存液泡（PSV），在那里它们转化为成熟亚基并积累。然而，大豆中储存蛋白运输所需的分子机制仍然很大程度上未知。在这项研究中，我们克隆了 OsGPA3 的唯一大豆同源物，它编码植物特有的高尔基体后囊泡运输的 kelch 重复调节因子，用于水稻储存蛋白分选。互补试验表明GmGPA3可以拯救水稻gpa3突变体。生化检测证实 GmGPA3 与 GmRab5 及其鸟嘌呤交换因子 (GEF) GmVPS9 发生物理相互作用。 GmGPA3的表达对GmVPS9对GmRab5a的GEF活性没有明显影响。值得注意的是，GmGPA3 的敲除扰乱了 mmRFP-CT10（一种用于 PSV 的人工货物）在发育中的大豆子叶中的运输。我们通过筛选酵母 cDNA 文库鉴定了两个假定的 GmGPA3 相互作用伴侣（GmGMG3 和 GmGMG11）。 GmGPA3 或 GmGMG3 的过度表达导致子叶细胞萎缩。我们的总体结果表明，GmGPA3 除了在介导大豆子叶中储存蛋白运输方面发挥保守作用外，还在细胞生长和发育中发挥重要作用。