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。 在多细胞生物体中，发育参数赋予了额外的一层 关于细胞器生物发生的遗传控制的复杂性； 尤其是，叶绿体的特性在不同物种之间差异很大 不同的细胞类型。不同叶绿体的生物化学和结构 对类型进行了详细描述。突变的表型现在可以指导我们 以其他方式隐藏的函数来确定 叶绿体的发育，并调节它们的组装。这个 玉米的复杂遗传学，其特征良好的转座子，大型 种子和叶片发育模式共同使其特别适合于 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 含有缺乏叶绿体各亚群的转座子Mu 蛋白质。这项建议关注的是其中六个突变体，它们的表型 提示在翻译后过程中涉及类囊体的损伤 膜组装，如蛋白质靶向或多亚基组装 复合体。将进一步研究它们的遗传特性，以确定 那些表现令人信服的，如Mu诱导的损伤。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 由这些突变定义的。将进行遗传杂交以定位 突变到染色体臂，以识别独立的等位基因，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，以及是否 基因专一作用于叶绿体，也可作用于非绿体。 几个最有趣的Mu诱发突变的分子克隆 将通过利用转座子标签进行分离。这些克隆人 将被用于获得相应的正常等位基因，然后将被 用作更详细的功能研究的工具。

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.