Identification of Nuclear Genes Regulated by Etioplast Differentiation

光合作用，即叶绿素和类胡萝卜素色素吸收的太阳能转化为储存的化学能，发生在绿色植物组织中，位于植物细胞的一个被称为质体的隔室中。叶绿体是进行光合作用的特殊质体类型，它含有这种过程所需的称为类囊体的内膜。不进行光合作用的非绿色植物组织含有其他特征性的质体类型，包括在黑暗生长的被子植物幼苗的胚叶中的质体。成熟的质体的标志是一个功能未知的次晶内膜，称为原板层体。当在地下发芽的黑暗生长的幼苗从土壤中出现时，光线会使黄化体分化成叶绿体。这些幼苗开始变绿色并形成光合作用活性的类囊体，这是由于浓缩在原片层体中的NADPH-原叶绿素氧化还原酶催化叶绿素的严格依赖于光的合成。这些蛋白质中超过95%由细胞核中DNA指定的基因编码，其余由小得多的质体基因组的基因编码。因为核编码的质体蛋白质是在胞质中而不是在质体中合成的，所以它们必须被输入到细胞区室中。已经进化出多种机制来帮助协调细胞核和叶绿体之间的基因表达和蛋白质产生。例如，几个不同的叶绿体到细胞核的信号转导途径，主要调节光合作用所需的核基因已被确定和部分表征。相比之下，在黑暗中通过叶绿体到细胞核的信号传导来调节核基因表达的可能性在变绿开始之前几乎还没有被探索过。（1）使用全基因组方法鉴定拟南芥的所有基因，作为其他植物物种的模型，其表达受暗生长幼苗中的黄化体发育的强烈调节，（2）利用独立的分析方法确定这些核基因的调控与叶肉体分化之间的联系。（3）确定暗培养和绿化幼苗中目的基因的表达模式以及相应蛋白产物的亚细胞定位和功能。本研究为探索植物细胞内质体与细胞核之间的通讯提供了基础。对这一过程的透彻理解是必不可少的，因为光依赖性叶绿体成熟是建立发芽幼苗光合能量代谢所必需的。 该项目的一个重要方面将是为培训研究生、本科生和博士后科研人员提供机会。研究的不同方面将提供适用于高等植物的当代分子遗传和生物化学方法。将鼓励有关研究人员通过公开介绍和外联活动传播其研究结果，并积极参加科学会议和专业协会。

Photosynthesis, the conversion of solar energy absorbed by chlorophyll and carotenoid pigments into stored chemical energy, takes place in green plant tissues within a compartment of the plant cell known as the plastid. The chloroplast, the specific plastid type that performs photosynthesis, contains internal membranes called thylakoids required for this process. Nongreen plant tissues that do not photosynthesize contain other characteristic plastid types, including the etioplast in the embryonic leaves of dark-grown angiosperm seedlings. The hallmark of maturing etioplasts is a paracrystalline inner membrane of unknown function termed the prolamellar body. When dark-grown seedlings that have germinated underground emerge from the soil, light causes etioplasts to differentiate into chloroplasts. Such seedlings begin to green and form photosynthetically active thylakoids due to the strictly light-dependent synthesis of chlorophyll catalyzed by the NADPH-protochlorophyllide oxidoreductase enzyme concentrated in the prolamellar body.Mature chloroplasts are thought to contain more than 3000 distinct proteins. More than 95 % of these proteins are encoded by genes specified by DNA in the nucleus and the remainder by the genes of the much smaller plastid genome. Because nuclear-encoded plastid proteins are synthesized in the cytosol rather than the plastid, they must be imported into that cellular compartment. Multiple mechanisms have evolved to help coordinate gene expression and protein production between the nucleus and the chloroplast. For example, several distinct chloroplast-to-nucleus signaling pathways that regulate primarily nuclear genes required for photosynthesis have been identified and partially characterized. In contrast, the potential for etioplast-to-nucleus signaling in the dark to regulate nuclear gene expression before greening begins has remained virtually unexplored.The research planned encompasses three main goals: (1) To use a whole genome approach to identify all genes of Arabidopsis, as a model for other plant species, whose expression is strongly regulated by etioplast development in dark-grown seedlings, (2) To confirm the link between etioplast differentiation and the regulation of these target nuclear genes using independent assays, (3) To determine target gene expression patterns, and the subcellular localization and function of the corresponding protein products in dark-grown and greening seedlings. This research will provide a basis for exploring communication within plant cells between the etioplast and the nucleus. A thorough understanding of this process is essential because light-dependent chloroplast maturation is required to establish photosynthetic energy metabolism in germinating seedlings. An important aspect of this project will be to provide opportunities for training scientific researchers at the graduate, undergraduate and postdoctoral levels. Different aspects of the research will provide exposure to contemporary molecular-genetic and biochemical methods applicable to higher plants. The researchers involved will be encouraged to disseminate their findings through public presentations and outreach activities, and to actively participate in scientific meetings and professional societies.