NUCLEAR GENES THAT MEDIATE CHLOROPLAST ASSEMBLY

线粒体和叶绿体的生物发生在遗传上是复杂的， 涉及分布在细胞核和细胞器之间的数百个基因。 在多细胞生物中，发育参数赋予了一个额外的层 复杂性的遗传控制的细胞器生物发生; 特别是质体的性质， 不同的细胞类型 不同质体的生物化学和结构 已经详细描述了类型。 突变的表型现在可以指导我们 否则隐藏的功能，确定的时间和定位， 叶绿体发育，并介导其组装。 的 复杂的玉米遗传学，其良好的转座子，大 种子，和叶片发育的模式，一起使它独特地适合于 对细胞器生物发生的发育方面的研究。 从一个玉米品系中分离出28个核突变体 携带转座子Mu，缺乏叶绿体的各种子集 proteins. 这项建议的重点是六个这些突变体，其表型 提示类囊体中涉及翻译后过程的损伤 膜组装，如蛋白质靶向或多亚基组装 配合物 它们的遗传特性将被进一步研究， 那些令人信服的表现就像是μ引起的损伤。 详细分析 在分子、生化和结构上的突变表型 水平将提供有关基因直接功能的线索 由这些突变所决定。 将进行遗传杂交以绘制 突变的染色体臂，以确定独立的等位基因，并 评估基因剂量对表型的影响。 发展研究将 解决叶片发育过程中基因作用的时间问题， 该基因特异性地作用于叶绿体，或者也作用于非绿色质体。 几个最有趣的Mu诱导突变的分子克隆 将通过利用转座子标签来分离。 这些克隆 将用于获得相应的正常等位基因，然后将其 用作更详细功能研究的工具。

The biogenesis of mitochondria and chloroplasts is genetically complex, involving hundreds of genes distributed between the nucleus and organelle. In multicellular organisms, developmental parameters confer an added layer of complexity upon the genetic control of organelle biogenesis; the properties of plastids, in particular, differ dramatically between different cell types. The biochemistry and structure of different plastid types have been described in detail. Mutant phenotypes can now direct us to otherwise hidden functions that determine the timing and localization of chloroplast development, and that mediate their assembly. The sophisticated genetics of maize, its well characterized transposons, large seed, and mode of leaf development, together make it uniquely suited for the study of developmental aspects of organelle biogenesis. Twenty-eight nuclear mutants have been isolated from a line of maize harboring the transposon Mu, that lack various subsets of chloroplast proteins. This proposal focuses on six of these mutants whose phenotypes suggest lesions in a post-translational process involved in thylakoid membrane assembly, such as protein targeting or assembly of multisubunit complexes. Their genetic properties will be further studied to identify those that behave convincingly like Mu-induced lesions. Detailed analyses of the mutant phenotypes at the molecular, biochemical, and structural levels will provide clues concerning the immediate function of genes defined by these mutations. Genetic crosses will be performed to map the mutations to a chromosome arm, to identify independent alleles, and to assess the effect of gene dosage on phenotype. Developmental studies will address the timing of gene action during leaf development and whether the gene acts specifically on chloroplasts, or on non-green plastids as well. Molecular clones of several of the most interesting Mu-induced mutations will be isolated by taking advantage of the transposon tag. These clones will be used to obtain the corresponding normal alleles, which will then be used as tools for more detailed functional studies.