Identification of Nuclear Genes Regulated by Etioplast Differentiation

光合作用，即叶绿素和类胡萝卜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被称为质体的一个隔间内。叶绿体是进行光合作用的一种特殊的质体类型，它含有一种称为类囊体的内部膜，这种膜是光合作用所必需的。不进行光合作用的非绿色植物组织含有其他特有的质体类型，包括深色生长的被子植物幼苗胚叶中的黄质体。成熟的病变体的标志是一个功能未知的被称为前层体的准晶内膜。当在地下发芽的暗色幼苗从土壤中出来时，光会使腐质体分化成叶绿体。这些幼苗开始变绿并形成具有光合活性的类囊体，这是由于叶绿素的合成严格依赖于光，由集中在原板层体中的nadph -原叶绿素内酯氧化还原酶催化。成熟的叶绿体被认为含有超过3000种不同的蛋白质。超过95%的这些蛋白质是由细胞核中DNA指定的基因编码的，其余的是由更小的质体基因组的基因编码的。因为核编码的质体蛋白是在细胞质溶胶中而不是在质体中合成的，所以它们必须被输入到细胞隔间中。多种机制已经进化，以帮助协调基因表达和蛋白质生产之间的细胞核和叶绿体。例如，几种不同的叶绿体到细胞核的信号通路已经被确定并部分表征，这些信号通路主要调节光合作用所需的核基因。相比之下，在绿化开始之前，在黑暗中，病质体到细胞核的信号传导调节核基因表达的潜力实际上尚未被探索。计划中的研究包括三个主要目标：(1)利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，这些基因的表达在黑暗生长的幼苗中受到黄质发育的强烈调控；(2)通过独立的测定来确认黄质分化与这些靶核基因的调控之间的联系；(3)确定靶基因的表达模式；以及暗生和绿化幼苗中相应蛋白产物的亚细胞定位和功能。该研究将为探索植物细胞内黄质与细胞核之间的通讯提供基础。深入了解这一过程是必要的，因为在发芽幼苗中需要光依赖的叶绿体成熟来建立光合能量代谢。该项目的一个重要方面是为培养研究生、本科生和博士后水平的科研人员提供机会。研究的不同方面将提供适用于高等植物的现代分子遗传和生化方法的机会。将鼓励参与的研究人员通过公开演讲和外联活动传播他们的发现，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.