Analysis of Protein Transport to the Vacuole in Plants as a Basis for the Production of Usefull Proteins in Higher Plants

液泡是许多植物营养细胞中最大的细胞器，其功能类似于动物的溶酶体，消化各种大分子物质，补充其成分。相反，植物贮藏组织中的液泡积累大量蛋白质，特别是贮藏蛋白，它们被称为蛋白质贮藏液泡。为了在基因工程植物中大量积累有用的蛋白质，了解贮藏蛋白质是如何选择性地运输到蛋白质贮藏液泡中的是很重要的，我们已经分析了甘薯孢子素在转化烟草细胞中的选择性运输机制，分别作为模式贮藏蛋白和作为模式表达系统。我们证明了孢子素前体N端前肽中的NPIR序列是液泡分选信号，并且NPIR信号介导的蛋白质液泡转运机制不同于其他几种液泡蛋白C端前肽中的疏水分选信号介导的蛋白质液泡转运机制。在本研究中，我们进一步扩展了我们的研究，并获得了以下结果：（1）NPIR信号作为空泡分选信号，即使它位于乘客蛋白的C-末端。(2)可溶性蛋白质的液泡转运需要一种类似于V型H^+-ATP酶的活性，它位于液泡前区室。(3)我们首次从植物中分离到了烟草中编码N-乙基马来酰亚胺敏感融合蛋白（NSF）同源蛋白的cDNA。

The vacuole is the largest organelle in many vegetative cells of plants, and it plays a function similar to animal lysosome to digest various macromolecules to replenish their constituents. In contrast, vacuoles in storage tissues of plants accumulate a large amount of proteins, in particular storage proteins, and they are called protein storage vacuoles. In order to aim large scale accumulation of usefull proteins in genetically engineered plants, it is important to understand how storage proteins are selectively transported to the protein storage vacuoles.We have previously analyzed the mechanisms involved in selective transport of sweetpotato sporamin, in transformed tobacco cells, as a model storage protein, and as a model expression system, respectively. We have shown that the NPIR sequencein the N-terminal propeptide of the precursor to sporamin is the vacuolar sorting signal, and that the mechanism of the vacuolar transport of proteins mediated by NPIR-signal is different from that mediated by the hydrophobic sorting signal located in the C-terminal propeptides of several other vacuolar proteins. In this study, we further extended our study, and obtained the following results ;(1) The NPIR-signal functions as a vacuolar sorting signal even when it is located at the C-terminus of the passenger protein. (2) The vacuolar transport of soluble proteins requires an activity similar to V-type H^+-ATPase which is localized in the pre-vacuolar compartment. (3) We isolated a cDNA of tobacco encoding a protein homologous to the N-ethylmaleimide-sensitive fusion protein (NSF) for the first time from the plant kingdom.