Genetic suppressors of Arabidopsis chloroplast protein import mutations

叶绿体是植物细胞的正常组成部分（这种亚细胞组成部分称为细胞器），在许多方面类似于自由生活的细菌。它们含有绿色色素，叶绿素，并专门负责光合作用的反应（这一过程使太阳能的捕获和使用，使有机产品）。由于光合作用是能量输入到生命世界的唯一重要机制，叶绿体具有不可估量的重要性，不仅对植物，而且对地球上的所有生命。叶绿体在许多其他方面也很重要，因为它们在脂质、氨基酸和淀粉的生物合成中起重要作用。虽然叶绿体确实含有DNA（这是它们作为自由生活的光合细菌的古老进化历史的遗物），因此能够编码它们自己的一些蛋白质，但构建一个功能齐全的叶绿体所需的大约3000种蛋白质中，>90%是在细胞核内的DNA上编码的。因此，大多数叶绿体蛋白质在叶绿体外合成，在称为细胞质的细胞基质中合成。由于叶绿体都被双层膜或包膜包围，蛋白质的被动运动是不受影响的，这就提出了一个重要的问题。为了克服这个问题，叶绿体已经进化出一种复杂的蛋白质输入装置，它使用能量（以ATP的形式）来驱动蛋白质从胞质溶胶输入，穿过包膜，进入叶绿体内部。这种蛋白质输入装置包括两个分子机器：一个在被称为Toc的外被膜中（“叶绿体外被膜处的转位子”的缩写），一个在被称为Tic的内被膜中。在过去的十年里，我们对蛋白质输入装置如何工作的理解取得了很大进展。特别是，该机制的大部分主要组成部分现在似乎已经确定。然而，我们的知识仍有很大差距。例如，虽然人们知道，在整个植物发育过程中，输入过程受到调节，但对这种调节的机制知之甚少。为了填补我们知识中的这些空白，需要采用全新的实验方法。本实验为研究叶绿体蛋白质输入提供了一种全新的方法。在以前的工作中，我们确定了携带影响蛋白质输入效率的基因突变的植物;我们在这里要做的是确定受这些突变影响的基因。由于叶绿体执行基本功能，并且由于蛋白质输入对于叶绿体发育是必不可少的，因此了解到叶绿体蛋白质输入机制有缺陷的植物无法存活超过胚胎阶段就不足为奇了。因此，叶绿体蛋白质的输入是植物必需的过程。同样，由于我们最终都依赖植物产品生存，因此叶绿体蛋白质的输入在全球范围内是必不可少的。更重要的是，由于叶绿体在许多经济上重要的产品（如脂质和淀粉）的合成中起着重要的作用，更全面地了解这些细胞器如何发展可能使我们能够提高作物的生产力，或以其他方式操纵它们的产品。

Chloroplasts are normal components of plant cells (such sub-cellular components are called organelles) that in many ways resemble free-living bacteria. They contain the green pigment, chlorophyll, and are exclusively responsible for the reactions of photosynthesis (the process that enables the capture of sunlight energy and its use to make organic products). Since photosynthesis is the only significant mechanism of energy-input into the living world, chloroplasts are of inestimable importance, not just to plants but to all life on Earth. Chloroplasts are also important in many other ways, since they play important roles in the biosynthesis of lipids, amino acids and starch. Although chloroplasts do contain DNA (a relic from their ancient, evolutionary past as free-living photosynthetic bacteria), and are therefore able to encode some of their own proteins, >90% of the 3000 or so proteins required to build a fully functional chloroplast are encoded on DNA within the cell nucleus. The majority of chloroplast proteins are therefore synthesized outside of the chloroplast, in the cellular matrix known as the cytosol. Since chloroplasts are each surrounded by a double membrane, or envelope, that is impervious to the passive movement of proteins, this presents a significant problem. In order to overcome the problem, chloroplasts have evolved a sophisticated protein import apparatus, which uses energy (in the form of ATP) to drive the import of proteins from the cytosol, across the envelope, and into the chloroplast interior. This protein import apparatus comprises two molecular machines: one in the outer envelope membrane called Toc (an abbreviation of 'Translocon at the outer envelope membrane of chloroplasts'), and one in the inner envelope membrane called Tic. Over the last decade, a great deal of progress has been made in our understanding of how this protein import apparatus works. In particular, it seems likely that most of the main components of the machinery have now been identified. Nevertheless, substantial gaps remain in our knowledge. For example, while it is known that the import process is regulated throughout plant development, very little is known about the mechanisms that underlie this regulation. To fill in these gaps in our knowledge, completely new experimental approaches will need to be employed. The experiments described in this proposal are an entirely new way of studying chloroplast protein import. In previous work, we identified plants carrying genetic mutations that affect the efficiency of protein import; what we propose to do here is to identify the genes affected by these mutations. Because chloroplasts carry out essential functions, and because protein import is essential for chloroplast development, it should come as no surprise to learn that plants with defective chloroplast protein import machinery are unable to survive beyond the embryo stage. Thus, chloroplast protein import is an essential process for plants. Similarly, since we are all ultimately dependent upon plant products for survival, it follows that chloroplast protein import is essential on a global scale. What is more, since chloroplasts play an instrumental role in the synthesis of many economically important products (such as lipids and starch), a more complete understanding of how these organelles develop may enable us to enhance the productivity of crop plants, or otherwise manipulate their products.