Molecular Analysis of Meiotic Recombination in Maize

在上一个奖项的任期内，在bz及其周围的重组事件的分子表征揭示了以下内容：（1）bz内的重组非常高，比玉米中的平均DNA片段高100倍。 (2)在bz的近端侧，主要由重复DNA组成，它至少低50倍。 (3)bz基因内的极性是均匀的，不像在酵母中那样显示极性。 (4)插入和成簇的单bp异源抑制重组，并具有使重组在基因间不均匀的作用。 (5)基因内序列多态性影响重组中间体的分辨率，导致几乎完全恢复亲本标记的IGR。 (6)基因转换，被认为是罕见的植物比酵母，似乎经常发生在非多态性杂合子。 (7)减数分裂重组表现出高保真性，并且没有致突变性。 玉米减数分裂重组的分析将通过结合bz基因座的遗传学和现代分子技术的力量而继续下去。 具体目标如下：（1）在不存在插入杂合性的情况下，检查单个bp多态性对重组连接分布的影响。(2)将bz处的重组分析扩展到5'上游区域。(3)分析存在和不存在异源性的基因转换带。(4)检测bz和最近的标记tac2094之间的所有“基因间”重组是否都发生在基因中同源减数分裂重组对于有性繁殖的生物体是必不可少的：它创造了新的基因型，并确保在第一次减数分裂时染色体正确分离。 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，从标记辅助选择理想的基因型到基于图位克隆有价值的基因。 然而，尽管它的重要性，我们的知识的过程中高等植物仍然是基本的。 玉米的青铜基因座是一个独特的优势系统，将用于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.