Molecular Analysis of Meiotic Recombination and Genomic Organization in the Bronze Region of Maize

同源减数分裂重组是有性生殖生物的一个重要过程：它通过重组染色体片段来创造新的基因型，否则染色体片段将作为一个单位遗传，并通过确保染色体在减数分裂时正确分离来促进生育。近一个世纪以来，遗传学家一直使用重组作为构建遗传图谱的工具，现在已经找到了实际应用范围，从遗传有害等位基因的风险预测，到标记辅助选择农业中理想的基因型，以及基于图谱的植物和动物中有价值基因的克隆。然而，尽管它很重要，我们对高等植物中同源减数细胞重组过程的了解与其他生物（如酵母）相比还很初级。这个项目将增加我们对玉米这一基本生物过程的理解，玉米既是研究重组的优秀模式生物，也是美国农业和工业的重要经济作物。本项目使用的遗传系统是影响种子色素沉着的bz位点，对重组研究具有独特的优势。本项目将结合bz地区遗传学的力量和现代分子工具的力量，继续对玉米减数分裂重组进行分析。最近的研究发现，在不同的玉米品系中，bz基因组区域的基因和反转录转座子的组织是多态性的。该项目有五个具体目标：1。分析缺乏杂合子异型中bz基因岛内的转换束长度，并将分析扩展到邻近的反转录转座子块。为了确定bz的明显转换极性，在基因的5‘和3’端检测到小的插入突变，而不是更多的位于中心的点突变，是由于突变的性质或位置。检测高度甲基化的反转录转座子块是否会影响邻近基因的重组。确定由基因和反转录转座子组成的区间内的所有重组连接是否都落在基因上。为了测试被不同系中不同数量的基因分开的两个基因组位点之间的重组是否与中间片段中共同基因的数量有关。

Homologous meiotic recombination is an important process for sexuallyreproducing organisms: it creates new genotypes by shuffling chromosomalsegments that otherwise would be inherited as a unit and promotes fertility byensuring that chromosomes segregate properly at meiosis. For close to a century,geneticists have been using recombination as a tool to construct genetic maps,which now find practical applications ranging from risk prediction for inheriteddeleterious alleles to marker-assisted selection of desirable genotypes inagriculture and map-based cloning of valuable genes in plants and animals. Yet,in spite of its importance, our knowledge of the process of homologous meioticrecombination in higher plants is rudimentary compared to other organisms, likeyeast. This project will increase our understanding of this basic biologicalprocess in maize, a plant that is both an excellent model organismfor studies of recombination, and an economically important crop in American agriculture and industry.The genetic system being used in the project is the bz locus, which affects seedpigmentation and is uniquely advantageous for studies of recombination. Thisproject will continue the analysis of meiotic recombination in maize by combining the power of the genetics of the bz region with that of modern molecular tools. It is greatly influenced by the recent finding that the organization of genes and retrotransposons in the bz genomic region is polymorphic in different maize lines. There are five specific objectives of the project:1. To analyze conversion tract lengths within the bz gene island in heterozygoteslacking heterologies and extend the analysis to adjacent retrotransposon blocks.2. To determine if the apparent conversion polarity at bz, detected with smallinsertion mutations at the 5' and 3' ends of the gene, but not with more centrallylocated point mutations, is due to the nature or the position of the mutations.3. To test whether the presence of a highly methylated retrotransposon blockaffects recombination in adjacent genes.4. To determine if all recombination junctions in an interval made up of genesand retrotransposons fall in genes.5. To test if recombination between two sites in the genome separated by adifferent number of genes in different lines is a function of the number ofcommon genes in the intervening segment.