Widespread recombination suppression facilitates plant sex chromosome evolution

Classical models suggest that recombination rates on sex chromosomes evolve in a stepwise manner to localize sexually antagonistic variants in the sex in which they are beneficial, thereby lowering rates of recombination between X and Y chromosomes. However, it is also possible that sex chromosome formation occurs in regions with pre-existing recombination suppression. To evaluate these possibilities, we constructed linkage maps and a chromosome-scale genome assembly for the dioecious plant Rumex hastatulus. This species has a polymorphic karyotype with a young neo-sex chromosome, resulting from a Robertsonian fusion between the X chromosome and an autosome, in part of its geographical range. We identified the shared and neo-sex chromosome using comparative genetic maps of the two cytotypes. We found that sex-linked regions of both the ancestral and the neo-sex chromosome are embedded in large regions of low recombination. Furthermore, our comparison of the recombination landscape of th...

经典模型表明，性染色体（sex chromosome）上的重组率（recombination rate）会以逐步方式演化，以便将性拮抗变异（sexually antagonistic variant）定位在其发挥有益作用的性别中，从而降低X与Y染色体之间的重组率。然而，性染色体的形成也可能发生在预先存在重组抑制（recombination suppression）的区域。为评估这两种可能性，我们构建了雌雄异株植物戟叶酸模（Rumex hastatulus）的连锁图谱（linkage map）与染色体级基因组组装（chromosome-scale genome assembly）。该物种在其部分地理分布范围内具有多态核型，拥有由X染色体与常染色体发生罗伯逊融合（Robertsonian fusion）形成的年轻新性染色体（neo-sex chromosome）。我们通过两种细胞型的比较遗传图谱，鉴定出了祖先性染色体与新性染色体。我们发现，祖先性染色体与新性染色体的性连锁区域均嵌入在大片低重组区域中。此外，我们对该物种重组景观（recombination landscape）的比较分析显示