鼠李科的系统发育研究

The reconstruction of phylogenetic trees of angiosperms families is one of key problems of plant phylogenetics. The family of Rhamnaceae contains 57 genera and c. 900 species, worldwide, particularly abundant in temperate and tropical regions. The phylogenetic tree of this family has not been reconstructed clearly. In this project, the molecular phylogenetic relationships of Rhamnaceae will be inferred using all the genera and multiple sequence segments from three genomes. The materials of 57 genera represented by 15% taxa of Rhamnaceae were collected across worldwide. A total of seven sequence segments with two from nuclear, four from plastid and one from mitochondrion will be used to reconstruct the phylogentic tree by different methods (Maximum parsimony, Maximum likelihood, and Bayesian inference). The monophyly of each genus and the evolutionary relationship among genera will be determined using this phylogenetic tree. Furthermore, the taxonomic data from literature, herbaria and field investigation will be examined systematically, and the synapomorphy for every genus will be mined. In addition, the tribal classification of Rhamnaceae will be revised under the phylogenetic framework. Finally, the ancestral status of each taxonomic character will be derived, and the character differences between lineages will be underlined on the view of evolution. Combining with multiple data, this project will resolve the problems including phylogenetic reconstruction, tribal classification as well as character evolution of Rhamnaceae. Also this project will greatly contribute to the further refined classification revision and other scientific studies on Rhamnaceae, giving direction for the optimal use and conservation plant resources of this family, and improving the scientific level on plant classification and molecular phylogenetics in our country.

被子植物科下属间系统发育关系重建是植物系统学研究的难点之一。本项目拟以被子植物重要类群鼠李科Rhamnaceae为研究对象重建该科的系统发育关系,解决其系统分类学残留问题。鼠李科包括58属约900种，世界广布，尤以温带和热带地区分布最为集中。本项目将在良好的前期工作基础上，基于合理的类群取样（涵盖全部现存57属和15%以上种类）和三个基因组的多个基因片段，用最大简约法、最大似然法和贝叶斯分析重建该科系统发育树，确认各属的单系性和演化关系；同时综合文献研究、标本查阅、野外调查，全面挖掘检测该科植物的分类学性状，确认各分支的共衍征，修订完善该科的分类系统；并追踪和推导分类性状的祖先状态，对各谱系间的性状差异从进化角度加以解释。本项目的实施将为鼠李科世界性种级水平的分类修订和其它研究提供框架，并为合理利用和保护该科植物资源提供参考，对提高我国在植物分类学和分子系统学领域的科研能力亦具有重要意义。

鼠李科因其广泛的地理分布和可能经历的早期快速辐射分化，是被子植物系统学研究的难点之一。本项目以该科为研究对象，选择Dirachimaceae、Barbeyaceae和胡颓子科Elaeagnaceae作为外类群。以属为单位，开展形态学的比较研究，同时选取多个分子片段，开展分子系统学研究，以澄清该科各分类单元之间的关系。结合化石资料，探讨本科系统发育重建困难的可能成因。研究结果显示，鼠李科是一个很好的单系类群，并得到形态学证据的支持。鼠李科可进一步划分为3个分支和11个族，但绝大多数分支和族的单系性和系统发育关系并没有得到很好的支持。在扩大样品数量引入大量缺失数据的情况下，鼠李科系统发育关系并没有发生明显改变，但却揭示出鼠李科部分属并非单系。虽然鼠李科11个族得到了形态学证据的支持，但3各分支的共衍征并未完全揭示。基于少量基因片段构建的系统发育结果和物种多样化速率分析显示鼠李科可能在40-50百万年前经历了快速辐射分化的过程，因此本项目在以上研究的基础上，利用最新的系统基因组学的方法，以族为单位选择代表类群，开展了叶绿体系统基因组学研究，并对拐枣Hovenia acerba开展了转录组学的比较研究，初步探讨了基因组数据在解析鼠李科系统发育关系中的价值。研究结果显示，选择的鼠李科代表类群的叶绿体基因组数据（全基因组数据或编码区数据）能够很好的解析类群之间的系统发育关系，转录组数据显示有大量的同源基因可供选择作为系统发育重建的数据来源。因此，后续工作应集中于组学数据的基础上开展相关的研究。