Mercier Raphaël, Jolivet Sylvie, Vezon Daniel, Huppe Emelyne, Chelysheva Liudmila, Giovanni Maité, Nogué Fabien, Doutriaux Marie-Pascale, Horlow Christine, Grelon Mathilde, Mézard Christine
Station de Génétique et d'Amélioration des Plantes, Institut National de la Recherche Agronomique, Versailles, France.
Curr Biol. 2005 Apr 26;15(8):692-701. doi: 10.1016/j.cub.2005.02.056.
Crossovers are essential for the completion of meiosis. Recently, two pathways of crossover formation have been identified on the basis of distinct genetic controls. In one pathway, crossover inhibits the occurrence of another such event in a distance-dependent manner. This phenomenon is known as interference. The second kind of crossover is insensitive to interference. The two pathways function independently in budding yeast. Only interference-insensitive crossovers occur in Schizosaccharomyces pombe. In contrast, only interference-sensitive crossovers occur in Caenorabditis elegans. The situation in mammals and plants remains unclear. Mer3 is one of the genes shown to be required for the formation of interference-sensitive crossovers in Saccharomyces cerevisiae.
To unravel the crossover status in the plant Arabidopsis thaliana, we investigated the role of the A. thaliana MER3 gene through the characterization of a series of allelic mutants. All mer3 mutants showed low levels of fertility and a significant decrease (about 75%) but not a total disappearance of meiotic crossovers, with the number of recombination events initiated in the mutants being similar to that in the wild-type. Genetic analyses showed that the residual crossovers in mer3 mutants did not display interference in one set of adjacent intervals.
Mutation in MER3 in Arabidopsis appeared to be specific to recombination events resulting in interference-sensitive crossovers. Thus, MER3 function is conserved from yeast to plants and may exist in other metazoans. Arabidopsis therefore has at least two pathways for crossover formation, one giving rise to interference-sensitive crossover and the other to independently distributed crossovers.
交叉互换对于减数分裂的完成至关重要。最近，基于不同的遗传控制，已鉴定出两种交叉互换形成途径。在一种途径中，交叉互换以距离依赖的方式抑制另一个此类事件的发生。这种现象被称为干涉。第二种交叉互换对干涉不敏感。这两种途径在芽殖酵母中独立发挥作用。在粟酒裂殖酵母中仅发生对干涉不敏感的交叉互换。相比之下，在秀丽隐杆线虫中仅发生对干涉敏感的交叉互换。哺乳动物和植物中的情况仍不清楚。Mer3是酿酒酵母中显示对形成干涉敏感的交叉互换所必需的基因之一。
为了阐明植物拟南芥中的交叉互换状态，我们通过对一系列等位基因突变体的表征研究了拟南芥MER3基因的作用。所有mer3突变体均表现出低育性水平，减数分裂交叉互换显著减少（约75%）但并未完全消失，突变体中起始的重组事件数量与野生型相似。遗传分析表明，mer3突变体中的残留交叉互换在一组相邻区间中未表现出干涉。
拟南芥中MER3的突变似乎特定于导致干涉敏感交叉互换的重组事件。因此，MER3的功能从酵母到植物都是保守的，并且可能存在于其他后生动物中。拟南芥因此至少有两种交叉互换形成途径，一种产生干涉敏感的交叉互换，另一种产生独立分布的交叉互换。
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