Data from: Recombination changes at the boundaries of fully and partially sex-linked regions between closely related Silene species pairs

The establishment of a region of suppressed recombination is a critical change during sex chromosome evolution, leading to such properties as Y (and W) chromosome genetic degeneration, accumulation of repetitive sequences and heteromorphism. Although chromosome inversions can cause large regions to have suppressed recombination, and inversions are sometimes involved in sex chromosome evolution, gradual expansion of the non-recombining region could potentially sometimes occur. We here test whether closer linkage has recently evolved between the sex-determining region and several genes that are partially sex-linked in Silene latifolia, using Silene dioica, a closely related dioecious plants whose XY sex chromosome system is inherited from a common ancestor. The S. latifolia pseudoautosomal region (PAR) includes several genes extremely closely linked to the fully Y-linked region. These genes were added to an ancestral PAR of the sex chromosome pair in two distinct events probably involving translocations of autosomal genome regions causing multiple genes to become partially sex-linked. Close linkage with the PAR boundary must have evolved since these additions, because some genes added in both events now show almost complete sex linkage in S. latifolia. We compared diversity patterns of five such S. latifolia PAR boundary genes with their orthologues in S. dioica, including all three regions of the PAR (one gene that was in the ancestral PAR and two from each of the added regions). The results suggest recent recombination suppression in S. latifolia, since its split from S. dioica.

重组抑制区域的建立是性染色体进化过程中的关键变革，由此催生了Y（及W）染色体的遗传退化、重复序列积累以及染色体异型性等特征。尽管染色体倒位可引发大范围区域的重组抑制，且倒位有时参与性染色体进化，但非重组区域的逐步扩张也可能在部分情况下发生。本研究以近缘雌雄异株植物异株蝇子草（Silene dioica）为实验材料——该物种的XY性染色体系统与白玉草（Silene latifolia）源自共同祖先——旨在检验白玉草的性别决定区域与若干部分性连锁基因之间，是否新近演化出了更为紧密的连锁关系。白玉草的假常染色体区域（pseudoautosomal region, PAR）包含数个与完全Y连锁区域紧密连锁的基因；这些基因通过两次独立事件被整合至性染色体对的祖先假常染色体区域中，这两次事件大概率涉及常染色体基因组区域的易位，使得多个基因成为部分性连锁基因。自这些基因整合事件发生以来，假常染色体区域边界与这些基因之间必然已演化出紧密的连锁关系，因为在两次事件中被添加的部分基因，如今在白玉草中已呈现出近乎完全的性连锁特征。我们将5个此类白玉草假常染色体区域边界基因的多样性模式，与其在异株蝇子草中的同源基因（orthologues）进行了比较，涵盖了假常染色体区域的全部三个区域：1个源自祖先假常染色体区域的基因，以及两个分别来自两个易位添加区域的基因。研究结果表明，自白玉草与异株蝇子草分化以来，白玉草中已新近出现了重组抑制现象。