基于RAD-seq技术的中国柳属皱纹柳亚属和黄花柳亚属的系统发育

Salix is a taxonomically difficult genus, due to dioecious and different time of development for flowers and leaves which prevents the observer from seeing all relevant characters on a single plant, and comparatively high frequency of natural interspecific hybrids. The genus has two major clades, subgenus Salix clade and Vetrix-Chamaetia clade. The relationships under two clades remained unresolved, especially the Vetrix-Chamaetia clade. The subgenera and sections of this clade are based on morphological characters, their boundaries are unclear. To elucidate the internal relationship of Vetrix-Chamaetia clade and evaluate present sectional classification, we will employ RAD-seq (restriction-site-associated DNA sequencing) conduct phylogenetic analysis covering 31 Chinese sections 65 species and 2 European sections 2 species of Vetrix-Chamaetia clade and 3 species as outgroup based on our previous work. Then we will reconstruct the evolutionary history of each chosen character according to the phylogeny. This study will provide more convincing bioinformatics evidence to understanding the Vetrix-Chamaetia clade. The work also will lay a foundation for the taxonomic revision of Salix in China.

柳属植物雌雄异株、通常先花后叶，很难在同一时间观察到同一种的雌花、雄花和成熟叶片的完整形态，加之种间存在广泛的自然杂交，分类研究极为困难。分子证据显示该属为一单系，属内分两支，一支为柳亚属，另一支主要由皱纹柳亚属和黄花柳亚属构成，但各分支内系统发育关系尚不明确，尤其是皱纹柳亚属和黄花柳亚属构成的次级分支。这一分支内的亚属和组完全基于宏观形态划分，亚属间界限模糊，组间界限也不清晰，是分类学研究中急需解决的问题。因此本课题在大量前期研究基础上，选用中国皱纹柳亚属和黄花柳亚属31组65种、欧洲的2组2种和外类群3种，利用限制性酶切位点关联DNA测序（RAD-seq）技术进行系统发育研究；并联合形态特征进行性状演化分析，对用于亚属和组划分的主要形态性状的系统学和分类学价值进行评价。通过本项目的研究，揭示中国皱纹柳亚属和黄花柳亚属内部系统发育关系，为中国柳属的全面修订提供科学依据证据。

柳属属内主要分两支，一支为柳亚属，另一支主要由皱纹柳亚属和黄花柳亚属构成，但各分支内系统发育关系尚不明确，尤其是皱纹柳亚属和黄花柳亚属构成的次级分支。本项目利用流式细胞技术和限制性酶切位点关联DNA测序（RAD-seq）等基因组测序技术，开展倍性测定、系统基因组学、分化时间估算、形态性状演化、生态位模型分析等研究探讨皱纹柳亚属和黄花柳亚属分支的演化历史。揭示了柳属在横断山及邻近地区的适应性辐射，厘清了欧亚大陆一些重要的多倍体柳的起源及亲本，对环纹矮柳进行了后选模式指定、描述进行了订正，对郝景盛发表的柳属新类群的进行了后选模式指定，对多枝柳的模式标本问题进行了修订，并发现了多枝柳是一个二倍体-四倍体的复合体。这为柳属的分类修订和多倍体物种形成的研究奠定了基础。