Crofts Andrew J, Washida Haruhiko, Okita Thomas W, Satoh Mio, Ogawa Masahiro, Kumamaru Toshihiro, Satoh Hikaru
Institute of Biological Chemistry, Washington State University, Pullman, WA 99164, USA.
Biochem Cell Biol. 2005 Dec;83(6):728-37. doi: 10.1139/o05-156.
Rice synthesizes and accumulates high levels of 2 distinct classes of seed storage proteins and sorts them to separate intracellular compartments, making it an ideal model system for studying the mechanisms of storage protein synthesis, transport, and deposition. In rice, RNA localization dictates the initial site of storage protein synthesis on specific subdomains of the cortical endoplasmic reticulum (ER), and there is a direct relation between the RNA localization site and the final destination of the encoded protein within the endomembrane system. Current data support the existence of 3 parallel RNA localization pathways leading from the nucleus to the actively synthesizing cortical ER. Additional pathways may exist for the synthesis of cytoplasmic and nuclear-encoded proteins targeted to organelles, the latter located in a stratified arrangement in developing endosperm cells. The study of rice mutants, which accumulate unprocessed glutelin precursors, indicates that these multiple pathways prevent nonproductive interactions between different classes of storage proteins that would otherwise disrupt protein sorting. Indeed, it appears that the prevention of disruptive interactions between different classes of storage proteins plays a key role in their biosynthesis in rice. In addition to highlighting the unique features of the plant endomembrane system and describing the relation between RNA and protein localization, this minireview will attempt to address a number of questions raised by recent studies on these processes.
水稻合成并积累高水平的两类不同的种子贮藏蛋白，并将它们分选到不同的细胞内区室，这使其成为研究贮藏蛋白合成、运输和沉积机制的理想模型系统。在水稻中，RNA定位决定了贮藏蛋白在皮质内质网（ER）特定亚结构域上的合成起始位点，并且RNA定位位点与编码蛋白在内膜系统中的最终目的地之间存在直接关系。目前的数据支持存在3条从细胞核到活跃合成的皮质内质网的平行RNA定位途径。对于靶向细胞器的细胞质和核编码蛋白的合成，可能还存在其他途径，后者在发育中的胚乳细胞中呈分层排列。对积累未加工谷蛋白前体的水稻突变体的研究表明，这些多条途径可防止不同类贮藏蛋白之间的非生产性相互作用，否则这些相互作用会破坏蛋白质分选。事实上，防止不同类贮藏蛋白之间的破坏性相互作用似乎在水稻中它们的生物合成中起关键作用。除了突出植物内膜系统的独特特征并描述RNA与蛋白质定位之间的关系外，本综述还将尝试解答最近关于这些过程的研究所提出的一些问题。
