Molecular Analysis of Meiotic Recombination in Maize

在前一个奖项的任期内，BZ及其周围的重组事件的分子特征表明：(1)BZ内的重组率非常高，是玉米平均DNA片段的100倍。(2)在以重复DNA为主的BZ近端，至少低50倍。(3)BZ基因内的重组是均匀的，不像在酵母中那样表现出极性。(4)插入和聚集单个碱基异源抑制重组，并使重组在整个基因中不均匀。(5)基因内序列多态影响重组中间产物的拆分，导致亲本标记的IGRs几乎完全恢复。(6)基因转换在植物中被认为比在酵母中更罕见，但似乎经常发生在非多态杂合子中。(7)减数分裂重组高保真，无致突变性。结合BZ基因座遗传学的力量和现代分子技术的力量，将继续进行玉米减数分裂重组的分析。具体目标如下：(1)在不存在插入杂合性的情况下，检测单个BP多态对重组连接点分布的影响。(2)将BZ的重组分析扩展到5‘上游区域。(3)分析存在和不存在异质性的基因转换区。(4)检验BZ与邻近标记Tac2094之间的所有“基因间”重组是否都发生在基因组中。同源减数分裂重组对有性生殖生物是必不可少的：它创造了新的基因类型，并确保了第一次减数分裂时适当的染色体分离。从实用的角度来看，它允许植物遗传学家构建具有多种应用的遗传图谱，从标记辅助选择所需的基因类型到基于图谱的有价值基因的克隆。然而，尽管它很重要，我们对高等植物中的这一过程的了解仍然很初级。玉米的青铜基因是一个独特的优势系统，将被用来阐明植物减数分裂重组的过程。

During the tenure of the previous award, molecular characterization of recombination events at and around bz has revealed the following: (1) Recombination within bz is very high, 100 times higher than in the average DNA segment in maize. (2) In the immediate proximal side of bz, consisting mostly of repetitive DNA, it is at least 50-fold lower. (3) Recombination within the bz gene is uniform and does not show polarity as it does in yeast. (4) Insertions and clustered single bp heterologies suppress recombination and have the effect of making recombination nonuniform across the gene. (5) Intragenic sequence polymorphisms affect resolution of the recombination intermediates, leading to an almost exclusive recovery of parentally marked IGRs. (6) Gene conversion, thought to be rarer in plants than in yeast, appears to occur frequently in nonpolymorphic heterozygotes. (7) Meiotic recombination exhibits high fidelity and is not mutagenic. The analysis of meiotic recombination in maize will be continued by combining the power of the genetics of the bz locus with that of modern molecular techniques. Specific aims are as follows:(1) Examine the effect of single bp polymorphisms on the distribution of recombination junctions in the absence of insertion heterozygosity.(2) Extend the analysis of recombination at bz to the 5' upstream region.(3) Analyze gene conversion tracts in the presence and absence of heterologies.(4) Test whether all "intergenic" recombination between bz and the closely proximal marker tac2094 occurs in genes.Homologous meiotic recombination is essential to sexually reproducing organisms: it creates novel genotypes and ensures proper chromosome segregation at the first meiotic division. From a practical standpoint, it allows plant geneticists to construct genetic maps that have multiple applications, from marker-assisted selection of desirable genotypes to the map-based cloning of valuable genes. Yet in spite of its importance, our knowledge of the process in higher plants remains rudimentary. The bronze locus of maize, a uniquely advantageous system, will be used to elucidate the process of meiotic recombination in plants.