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体的一个重要过程：它通过改组原本作为一个单位遗传的染色体片段来创造新的基因类型，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，现在已经发现了实际应用，从遗传有害等位基因的风险预测到农业中理想的基因类型的标记辅助选择，以及基于图谱的动植物有价值基因的克隆。然而，尽管它很重要，但与酵母等其他生物相比，我们对高等植物中同源减数分裂重组过程的了解是初级的。这个项目将增加我们对玉米这一基本生物过程的了解，玉米既是研究重组的优秀模式组织，也是美国农业和工业中重要的经济作物。该项目使用的遗传系统是BZ基因座，它影响种子着色，对重组研究具有独特的优势。该项目将结合BZ区遗传学的力量和现代分子工具的力量，继续分析玉米减数分裂重组。BZ基因组区域的基因和反转录转座子的组织在不同的玉米品系中是多态的，这一发现极大地影响了这一发现。该项目有五个具体目标：1.分析缺乏异质性的杂合子中BZ基因岛内的转换道长度，并将分析扩展到邻近的反转录转座子区块。确定基因5‘端和3’端的小插入突变而不是更中心的点突变检测到的BZ的表观转换极性是否与突变的性质或位置有关。测试高甲基化反转录转座子的存在是否会影响相邻基因的重组。以确定在由基因和反转录转座子组成的区间内是否所有重组连接都落在基因中。为了测试基因组中被不同品系中不同数量的基因隔开的两个位置之间的重组是否是中间片段中共同基因数量的函数。

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.