Control of Storage Protein Biosynthesis by mRNA Targeting

植物种子的主要代谢活动是合成碳（以脂类和淀粉的形式）和氮（以贮藏蛋白的形式）储备。 虽然看起来是独立的过程，碳和氮代谢是相互关联的，如在这两个过程之一中基因表达改变的确定的遗传突变体和转基因植物所表现出的几乎平行的反应所证明的。 负责碳和氮储备的这种协调表达的机制尚不清楚。 本基金申请提出了一系列关于氮代谢的一个方面的研究，即水稻胚乳发育过程中贮藏蛋白生物合成的控制。 水稻是研究贮藏蛋白生物合成的极好系统，因为它合成和积累两大类贮藏蛋白，醇溶蛋白和谷蛋白，后者是11S球蛋白。 此外，大米将这些蛋白质储存在不同的亚细胞区室中。 谷醇溶蛋白直接沉积在内质网（ER）腔内的脑池内的蛋白质颗粒，而谷蛋白通过内膜系统运输到蛋白质储存泡。 本实验室先前的研究已经证明，编码这两类储存蛋白的RNA并不以随机的方式定位在ER上。 相反，醇溶谷蛋白mRNA高度富集在结合醇溶谷蛋白蛋白体（PB）的ER膜上，而谷蛋白mRNA主要在池状ER上。 醇溶谷蛋白mRNA定位于醇溶谷蛋白PB通过从细胞核定向RNA转运发生。 为了更好地理解这一过程，将进行研究，以确定指导RNA运输和定位的核苷酸序列，并确定和表征蛋白质，这是负责运输和锚定醇溶谷蛋白和谷蛋白RNA的醇溶谷蛋白PB和池ER，分别。 由于RNA转运是通过颗粒的形成和移动而发生的，因此将努力分离这些RNA转运颗粒并确定可能共转运的其他RNA种类。 将采取综合方法来实现这些目标，并将结合使用生物化学，细胞，分子和超微结构技术。 这项研究将提供关于RNA和蛋白质如何在植物细胞中分类以及ER如何分化为具有特定功能的独特结构域的新信息。 此外，它将导致对可能控制碳和氮的利用及其转化为储存储备的机制的新见解。

The major metabolic activities of plant seeds are directed toward the synthesis of carbon (in the form of lipids and starch) and nitrogen (in the form of storage proteins) reserves. Although appearing to be independent processes, carbon and nitrogen metabolism are inter-related as evidenced by the near parallel responses exhibited by defined genetic mutants and transgenic plants altered in gene expression in one of these two processes. The mechanisms responsible for this coordinated expression of carbon and nitrogen reserves are not known. This grant application proposes a series of studies on one aspect of nitrogen metabolism, i.e. the control of storage protein biosynthesis in developing rice endosperm. Rice is an excellent system to study storage protein biosynthesis as it synthesizes and accumulates both major classes of storage proteins, prolamines and glutelins, the latter an 11S globulin. Moreover, rice stores these proteins in different subcellular compartments. Prolamines are deposited directly as protein intracisternal granules within the endoplasmic reticulum (ER) lumen, whereas glutelins are transported through the endomembrane system to a protein storage vacuole. Previous studies from this laboratory have demonstrated that the RNAs encoding these two classes of storage proteins are not localized in a stochastic fashion on the ER. Instead, prolamine mRNAs are highly enriched on the ER membranes that bind the prolamine protein bodies (PBs) whereas glutelin mRNAs are predominant on the cisternal ER. The localization of prolamine mRNAs to the prolamine PBs occurs by directed RNA transport from the nucleus. To better understand this process, studies will be undertaken to identify the nucleotide sequences that direct RNA transport and localization and to identify and characterize proteins, which are responsible for the transport and anchoring of prolamine and glutelin RNAs to the prolamine PBs and cisternal ER, respectively. As RNA transport occurs by the formation and movement of particles, efforts will be made to isolate these RNA transport particles and determine what other RNA species may be co-transported. An integrated approach will be taken to achieve these goals, and will incorporate the use of biochemical, cellular, molecular and ultrastructural techniques. This study will provide new information on how RNAs and, in turn, proteins are sorted in plant cells and how the ER can differentiate into unique domains with specific functions. Moreover, it will lead to new insights into the mechanisms that may control utilization of carbon and nitrogen and their conversion into storage reserves.