Crossovers create genetic diversity and are required for equal chromosome segregation during meiosis. Crossover number and distribution are highly regulated by different mechanisms that are not yet fully understood, including crossover interference. The chromosome axis is crucial for crossover formation. Here, we explore the function of the axis protein ASYNAPSIS3. To this end, we use the allotetraploid species Brassica napus; due to its polyploid nature, this system allows a fine-grained dissection of the dosage of meiotic regulators. The simultaneous mutation of all four ASY3 alleles results in defective synapsis and drastic reduction of crossovers, which is largely rescued by the presence of only one functional ASY3 allele. Crucially, while the number of class I crossovers in mutants with two functional ASY3 alleles is comparable to that in wild type, this number is significantly increased in mutants with only one functional ASY3 allele, indicating that reducing ASY3 dosage increases crossover formation. Moreover, the class I crossovers on each bivalent in mutants with one functional ASY3 allele follow a random distribution, indicating compromised crossover interference. These results reveal the distinct dosage-dependent effects of ASY3 on crossover formation, and provide insights into the role of the chromosome axis in patterning recombination.

中文翻译：

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ASYNAPSIS3 对甘蓝型油菜减数分裂交叉形成具有多种剂量依赖性影响


交叉创造了遗传多样性，是减数分裂过程中染色体平等分离所必需的。交叉数量和分布受到尚未完全理解的不同机制的高度调控，包括交叉干扰。染色体轴对于交叉形成至关重要。在这里，我们探讨轴蛋白 ASYNAPSIS3 的功能。为此，我们使用异源四倍体物种甘蓝型油菜；由于其多倍体性质，该系统可以对减数分裂调节剂的剂量进行细粒度的剖析。所有四个 ASY3 等位基因的同时突变导致突触缺陷和交叉的急剧减少，这在很大程度上是通过仅存在一个功能性 ASY3 等位基因来挽救的。至关重要的是，虽然具有两个功能性 ASY3 等位基因的突变体中 I 类交换的数量与野生型相当，但在仅具有一个功能性 ASY3 等位基因的突变体中，该数量显着增加，表明减少 ASY3 剂量会增加交换形成。此外，具有一个功能性 ASY3 等位基因的突变体中每个二价的 I 类交叉遵循随机分布，表明交叉干扰受损。这些结果揭示了 ASY3 对交叉形成的独特剂量依赖性影响，并提供了对染色体轴在模式重组中的作用的见解。