Wheat seed storage proteins (prolamins) are important for the grain quality because they provide a characteristic texture to wheat flour products. In wheat endosperm cells, prolamins are transported from the Endoplasmic reticulum to Protein storage vacuoles through two distinct pathways—a conventional pathway passing through the Golgi apparatus and an unconventional Golgi-bypassing pathway during which prolamins accumulate in the ER lumen, forming Protein bodies. Unfortunately, transport studies conducted previously achieved limited success because of the seed-specificity of the latter pathway and the multigene architecture of prolamins. To overcome this difficulty, we expressed either of the two families of wheat prolamins, namely α-gliadin or High-molecular-weight subunit of glutenin, in soybean seed, which naturally lacks prolamin-like proteins. SDS-PAGE analysis indicated the successful expression of recombinant wheat prolamins in transgenic soybean seeds. Their accumulation states were quite different—α-gliadin accumulated with partial fragmentation whereas the HMW-glutenin subunit formed disulfide-crosslinked polymers without fragmentation. Immunoelectron microscopy of seed sections revealed that α-gliadin was transported to PSVs whereas HMW-glutenin was deposited in novel ER-derived compartments distinct from PSVs. Observation of a developmental stage of seed cells showed the involvement of post-Golgi Prevacuolar compartments in the transport of α-gliadin. In a similar stage of cells, deposits of HMW-glutenin surrounded by membranes studded with ribosomes were observed confirming the accumulation of this prolamin as ER-derived PBs. Subcellular fractionation analysis supported the electron microscopy observations. Our results should help in better understanding of molecular events during the transport of prolamins in wheat.

小麦种子储存蛋白（谷醇溶蛋白）对于谷物质量很重要，因为它们为小麦面粉产品提供了特有的质地。在小麦胚乳细胞中，谷醇溶蛋白通过两种不同的途径从内质网转运到蛋白质储存液泡——穿过高尔基体的传统途径和绕过高尔基体的非常规途径，在此过程中谷醇溶蛋白在内质网腔中积累，形成蛋白体。不幸的是，由于后一种途径的种子特异性和谷醇溶蛋白的多基因结构，之前进行的转运研究取得的成功有限。为了克服这个困难，我们在大豆种子中表达了两个小麦谷醇溶蛋白家族中的任何一个，即α-麦醇溶蛋白或麦谷蛋白的高分子量亚基，而大豆种子天然缺乏谷醇溶蛋白样蛋白质。 SDS-PAGE分析表明重组小麦谷醇溶蛋白在转基因大豆种子中成功表达。它们的积累状态完全不同——α-麦醇溶蛋白积累并部分断裂，而HMW-麦谷蛋白亚基形成二硫键交联聚合物而没有断裂。种子切片的免疫电镜显示，α-麦醇溶蛋白被转运至 PSV，而 HMW-麦谷蛋白沉积在与 PSV 不同的新型 ER 衍生区室中。对种子细胞发育阶段的观察表明，高尔基体后液泡区室参与了 α-麦醇溶蛋白的运输。在类似的细胞阶段，观察到 HMW-麦谷蛋白沉积物被布满核糖体的膜包围，证实了这种谷醇溶蛋白作为 ER 衍生的 PB 的积累。亚细胞分级分析支持电子显微镜观察。 我们的结果应该有助于更好地理解小麦中谷醇溶蛋白运输过程中的分子事件。