Department of Applied Genetics and Cell Biology and Department of Chemistry, University of Natural Resources and Applied Life Sciences, 1190 Vienna, Austria.
Plant Physiol. 2010 Jun;153(2):693-702. doi: 10.1104/pp.109.152363. Epub 2010 Apr 13.
Zeins are the major storage proteins in maize (Zea mays) endosperm, and their accumulation in zein bodies derived from the endoplasmic reticulum is well characterized. In contrast, relatively little is known about post-Golgi compartments or the trafficking of vacuolar proteins in maize endosperm, specifically the presence of globulins in structures resembling protein storage vacuoles that appear in early to mid-stage seed development. We investigated this pathway by expressing and analyzing a recombinant reporter glycoprotein during endosperm maturation, using a combination of microscopy and sensitive glycopeptide analysis. Specific N-glycan acceptor sites on the protein were followed through the stages of grain development, revealing a shift from predominantly paucimannosidic vacuolar glycoforms to predominantly trimmed glycan structures lacking fucose. This was accompanied by a change in the main subcellular localization of the protein from large protein storage vacuole-like post-Golgi organelles to the endoplasmic reticulum and zein bodies. The endogenous storage proteins corn alpha-globulin and corn legumin-1 showed a similar spatiotemporal profile both in transgenic plants expressing the reporter glycoprotein and in wild-type plants. This indicates that the shift of the intracellular trafficking route, as observed with our reporter glycoprotein, may be a common strategy in maize seed development.
玉米胚乳中的 Zein 是主要的储存蛋白，其在内质网衍生的 Zein 体中的积累已得到很好的描述。相比之下，人们对玉米胚乳中高尔基体后区室或液泡蛋白的运输途径知之甚少，特别是在早期到中期种子发育过程中，类似蛋白储存液泡的结构中存在球蛋白。我们通过在胚乳成熟过程中表达和分析重组报告糖蛋白，并结合显微镜和敏感糖肽分析，研究了这条途径。通过研究该蛋白的特定 N-糖基化接受位点在谷物发育阶段的变化，揭示了从主要是低甘露糖型液泡糖型向主要是无岩藻糖的修剪聚糖结构的转变。这伴随着蛋白的主要亚细胞定位从大的蛋白储存液泡样高尔基体后区室到内质网和 Zein 体的改变。内源性储存蛋白玉米α-球蛋白和玉米豆球蛋白-1在表达报告糖蛋白的转基因植物和野生型植物中都表现出相似的时空表达谱。这表明，与我们的报告糖蛋白观察到的细胞内运输途径的转变可能是玉米种子发育的一种常见策略。
