Abstract：
BACKGROUND: Salicaceae species have diverse sex determination systems and frequent sex chromosome turnovers. However, compared with poplars, the diversity of sex determination in willows is poorly understood, and little is known about the evolutionary forces driving their turnover. Here, we characterized the sex determination in two Salix species, S. chaenomeloides and S. arbutifolia, which have an XY system on chromosome 7 and 15, respectively.
RESULTS: Based on the assemblies of their sex determination regions, we found that the sex determination mechanism of willows may have underlying similarities with poplars, both involving intact and/or partial homologs of a type A cytokinin response regulator (RR) gene. Comparative analyses suggested that at least two sex turnover events have occurred in Salix, one preserving the ancestral pattern of male heterogamety, and the other changing heterogametic sex from XY to ZW, which could be partly explained by the \"deleterious mutation load\" and \"sexually antagonistic selection\" theoretical models. We hypothesize that these repeated turnovers keep sex chromosomes of willow species in a perpetually young state, leading to limited degeneration.
CONCLUSIONS: Our findings further improve the evolutionary trajectory of sex chromosomes in Salicaceae species, explore the evolutionary forces driving the repeated turnovers of their sex chromosomes, and provide a valuable reference for the study of sex chromosomes in other species.
RESULTS: Based on the assemblies of their sex determination regions, we found that the sex determination mechanism of willows may have underlying similarities with poplars, both involving intact and/or partial homologs of a type A cytokinin response regulator (RR) gene. Comparative analyses suggested that at least two sex turnover events have occurred in Salix, one preserving the ancestral pattern of male heterogamety, and the other changing heterogametic sex from XY to ZW, which could be partly explained by the \"deleterious mutation load\" and \"sexually antagonistic selection\" theoretical models. We hypothesize that these repeated turnovers keep sex chromosomes of willow species in a perpetually young state, leading to limited degeneration.
CONCLUSIONS: Our findings further improve the evolutionary trajectory of sex chromosomes in Salicaceae species, explore the evolutionary forces driving the repeated turnovers of their sex chromosomes, and provide a valuable reference for the study of sex chromosomes in other species.
摘要：
背景：杨柳科物种具有不同的性别决定系统和频繁的性染色体周转。然而,与杨树相比，人们对柳树性别决定的多样性知之甚少，对推动他们更替的进化力量知之甚少。这里,我们描述了两种柳柳的性别决定，S.chaenomelides和S.arbutifolia，它们分别在染色体7和15上具有XY系统。
结果：根据其性别决定区域的集合，我们发现柳树的性别决定机制可能与杨树有潜在的相似之处，均涉及A型细胞分裂素反应调节因子（RR）基因的完整和/或部分同源物。比较分析表明，至少有两个性别更替事件发生在沙柳，一个保留了男性异性恋的祖先模式，另一个从XY到ZW的异性恋改变，这可以部分解释为“有害突变负荷”和“性拮抗选择”理论模型。我们假设这些反复的失误使柳树物种的性染色体保持在永远年轻的状态，导致有限的退化。
结论：我们的发现进一步改善了杨柳科物种性染色体的进化轨迹，探索推动其性染色体反复翻转的进化力量，为其他物种性染色体的研究提供有价值的参考。
结果：根据其性别决定区域的集合，我们发现柳树的性别决定机制可能与杨树有潜在的相似之处，均涉及A型细胞分裂素反应调节因子（RR）基因的完整和/或部分同源物。比较分析表明，至少有两个性别更替事件发生在沙柳，一个保留了男性异性恋的祖先模式，另一个从XY到ZW的异性恋改变，这可以部分解释为“有害突变负荷”和“性拮抗选择”理论模型。我们假设这些反复的失误使柳树物种的性染色体保持在永远年轻的状态，导致有限的退化。
结论：我们的发现进一步改善了杨柳科物种性染色体的进化轨迹，探索推动其性染色体反复翻转的进化力量，为其他物种性染色体的研究提供有价值的参考。
