Data from: Single locus sex determination and female heterogamety in the basket willow (Salix viminalis L.)

Most eukaryotes reproduce sexually and a wealth of different sex determination mechanisms have evolved in this lineage. Dioecy or separate sexes are rare among flowering plants but have repeatedly evolved from hermaphroditic ancestors possibly involving male or female sterility mutations. Willows (Salix spp.) and poplars (Populus spp.) are predominantly dioecious and are members of the Salicaceae family. All studied poplars have sex determination loci on chromosome XIX, however, the position differs among species and both male and female heterogametic system exists. In contrast to the situation in poplars, knowledge of sex determination mechanisms in willows is sparse. In the present study, we have for the first time positioned the sex determination locus on chromosome XV in S. viminalis using quantitative trait locus mapping. All female offspring carried a maternally inherited haplotype, suggesting a system of female heterogamety or ZW. We used a comparative mapping approach and compared the positions of the markers between the S. viminalis linkage map and the physical maps of S. purpurea, S. suchowensis and P. trichocarpa. As we found no evidence for chromosomal rearrangements between chromosome XV and XIX between S. viminalis and P. trichocarpa, it shows that the sex determination loci in the willow and the poplar most likely do not share a common origin and has thus evolved separately. This demonstrates that sex determination mechanisms in the Salicaceae family have a high turnover rate and as such it is excellent for studies of evolutionary processes involved in sex chromosome turnover.

绝大多数真核生物以有性生殖方式繁衍，该演化支中演化出了丰富多样的性别决定机制。雌雄异株（dioecy）在被子植物中较为罕见，但该类群已多次从雌雄同株的祖先类群演化而来，此过程可能涉及雄性或雌性育性丧失的突变。柳属（Salix spp.）植物与杨属（Populus spp.）均以雌雄异株为主要生殖方式，同属于杨柳科（Salicaceae）。目前已研究的所有杨树的性别决定位点均位于19号染色体（chromosome XIX）上，但不同物种的位点位置存在差异，且同时存在雄性异配与雌性异配两种性别决定系统。与杨树的研究基础相比，学界对柳属植物性别决定机制的认知仍较为匮乏。本研究首次通过数量性状位点（quantitative trait locus, QTL）定位技术，将旱柳（S. viminalis）的性别决定位点定位于15号染色体（chromosome XV）上。所有雌性后代均携带母本遗传的单倍型，这提示该物种的性别决定系统为雌性异配型（ZW型）。本研究采用比较定位策略，对比了旱柳连锁图谱（linkage map）与紫柳（S. purpurea）、簸箕柳（S. suchowensis）以及毛果杨（P. trichocarpa）的物理图谱（physical map）中分子标记的位置。通过比对发现，旱柳的15号染色体与毛果杨的19号染色体之间未检测到染色体重排（chromosomal rearrangements）现象，这表明柳属与杨属的性别决定位点很可能并非起源于共同的祖先，而是各自独立演化而来。该研究结果证实，杨柳科植物的性别决定机制具有极高的演化更替速率，因此是研究性染色体演化更替相关进化过程的理想模型。