Molecular Mechanisms of Chloroplast Division in Higher Plants

小行星9604412 技术摘要：细胞器复制对所有真核生物的生长和发育至关重要。 然而，关于细胞器分裂的分子机制或它们的数量是如何控制的知之甚少。 Osteryoung博士已经从拟南芥中鉴定出一个cDNA，命名为cpFtsZ，它可能在叶绿体分裂中起着核心作用。 该核基因编码细菌蛋白FtsZ的叶绿体定位同源物。 FtsZ是细菌细胞分裂机制的关键结构组分，其在细菌胞质分裂期间在分裂位点组装以形成环状结构。 真核生物cpFtsZ的发现表明，细胞器和原核生物的分裂机制是相似的，并首次打开了真核生物细胞器分裂过程的分子解剖的大门。 本项目的目标是开始详细分析cpFtsZ在叶绿体分裂中的作用，使用拟南芥作为模型系统。 为了检验cpFtsZ对于叶绿体分裂是重要的这一假设，将产生具有增强或降低的cpFtsZ表达的转基因植物，并且将评估这种遗传操作对叶绿体数目的影响。 cpFtsZ基因是否映射到和/或补充拟南芥中影响叶绿体分裂的任何已知突变的问题将得到解决。 叶绿体内的cpFtsZ蛋白的定位将在分裂和非分裂叶绿体中进行研究。 cpFtsZ表达和叶绿体分裂之间的关系将通过分析cpFtsZ表达与叶绿体分裂模式的空间和时间模式来检查。 由于初步的数据表明，有多个FtsZ同源拟南芥中，额外的FtsZ相关基因将被分离和亚细胞定位的基因产物将被建立。 另外的质体定位FtsZ同源物，如果现存的话，将表明在不同的细胞类型或相关蛋白质之间的功能异质性的差异调节的可能性。 这个项目的长期目标是建立一个全面的模型，描述高等植物叶绿体分裂的生化和分子过程。 通俗语言摘要： 在植物中，叶绿体是负责光合作用的关键亚细胞器，光合作用是将太阳能转化为化学能的过程，即， 通过二氧化碳和水的光化学转化为糖。 这一基本的生命过程使我们所知的许多生命（植物和动物）能够在地球上存在。叶绿体通常被认为是从自由生活的细菌进化而来的，这些细菌与其他细胞形成了密切的共生（内共生）关系。 虽然叶绿体的大部分成分是由植物细胞核基因编码的基因产物组成的，但叶绿体仍然是半自主的，因为它们有自己的基因和蛋白质合成机制，并且它们通过分裂过程增加数量，就像细胞分裂一样。 当植物细胞分裂时，因为它们必须随着植物的生长和发育而分裂，所以叶绿体也分裂，以便它们可以分布在后代细胞中，这是至关重要的。 这是如何发生的，至今仍是一个谜。 Osteryoung博士在植物中发现了一个基因，该基因与在细菌细胞分裂中起关键作用的基因同源。 她假设这种蛋白质在叶绿体分裂中的功能与它在细菌细胞分裂中的功能相似。 这个项目的目的就是检验这个假设。 这项研究的结果有望促进我们对叶绿体如何分裂的理解，以便在生长和发育的植物的各种细胞中正确分布。 ***

9604412 Osteryoung Technical abstract: Organelle replication is critical for growth and development in all eukaryotes. However, very little is known about the molecular mechanisms by which organelles divide or how their numbers are controlled. Dr. Osteryoung has identified a cDNA from Arabidopsis thaliana, designated cpFtsZ, that may play a central role in the division of chloroplasts. This nuclear gene encodes a chloroplast-localized homologue of the bacterial protein FtsZ. FtsZ is a key structural component of the bacterial cell division machinery that assembles to form a ring-like structure at the division site during bacterial cytokinesis. Discovery of eukaryotic cpFtsZ suggests that division mechanisms in organelles and prokaryotes are similar, and for the first time opens the door to a molecular dissection of the organelle division process in eukaryotes. The goal of this project is to begin a detailed analysis of the role of cpFtsZ in chloroplast division, using Arabidopsis thaliana as a model system. To test the hypothesis that cpFtsZ is important for chloroplast division, transgenic plants will be generated with enhanced or reduced expression of cpFtsZ, and the effect of such genetic manipulations on chloroplast number will be assessed. The question of whether the cpFtsZ gene maps to and/or complements any of the known mutations in Arabidopsis that affect chloroplast division will be addressed. The localization of the cpFtsZ protein within the chloroplast will be investigated in dividing and non-dividing chloroplasts. The relationship between cpFtsZ expression and chloroplast division will be examined by analyzing the spatial and temporal patterns of cpFtsZ expression in relation to patterns of chloroplast division. Because preliminary data suggest that there are multiple FtsZ homologues in Arabidopsis, additional FtsZ related genes will be isolated and the subcellular localization of their gene products will be established. Additional plastid-localized FtsZ homologues , if extant, would suggest the possibility of differential regulation in different cell types or of functional heterogeneity among related proteins. The longer-term goal of this project is to develop a comprehensive model describing the biochemical and molecular processes that govern chloroplast division in higher plants. Lay-language abstract: In plants, the chloroplast is the key subcellular organelle that is responsible for photosynthesis, the process that converts sunlight energy to a form of chemical energy, i.e., through photochemical conversion of carbon dioxide plus water to sugar. This fundamental life process is what enables much of life (plants and animals) as we know it to exist on earth. Chloroplasts are generally regarded as having evolved from free-living bacteria that entered into a close symbiotic (endosymbiotic) relationship with other cells. Although most of the components of the chloroplasts are made of gene products encoded by the plant cell's nuclear genes, chloroplasts are nonetheless semi-autonomous, in that they have their own genes and protein synthetic machinery, and they increase in number by a process of division much like cell division. When plant cells divide, as they must as the plant grows and develops, it is critical that the chloroplasts also divide so that they can be distributed among the progeny cells. How this occurs is as yet a mystery. Dr. Osteryoung has discovered a gene in plants that is homologous to a gene that plays a key role in bacterial cell division. She hypothesizes that this protein functions in chloroplast division in a manner similar to how it functions in bacterial cell division. The goal of this project is to test this hypothesis. The results of this research are expected to advance our understanding of how chloroplasts divide in order to be properly distributed among the various cells of a growing and developing plant. ***