初探低拷贝核基因在低等分类阶元系统发育重建中的适用性——以十字花科为例

分子系统学已被广泛用于解决物种之间的亲缘关系。迄今为止，被子植物分子系统学大都采用叶绿体和线粒体基因。但叶绿体和线粒体多数采用单亲遗传方式，不能完全记录物种的进化历史。而且叶绿体和线粒体基因相对保守，可用于系统发育重建的信息有限，很难用来解决科以下类群之间的亲缘关系。相反，核基因遵守双亲遗传方式并能提供大量信息位点，但却没有得到广泛运用。本文以十字花科为例，从17种十字花科植物中得到了5个编码蛋白的单拷贝核基因序列，采用最大简约法、最大似然法和贝叶斯法重建它们之间的亲缘关系。结果表明，和目前常用的基因相比，这些基因能提供更多的信息位点，由此得到的系统发育树具有很高的支持，利用最大简约法得到的5个核基因的系统树中各分支均得到了100%的自展支持率。结果表明，我们选取的核基因可以用来进行科、属及种间的系统发育重建。因此，这5个基因可以用来解决被子植物其它科内的亲缘关系，而且也可以作为DNA条形码研究的有效分子标记。

The Use of Low-copy Nuclear Genes for Reconstructing thePhylogeny of Low-level Taxonomic Hierarchies: Evidence from Brassicaceae

Molecular systematics is widely used to determine organismal relationships. However, until now, systematics of angiosperms has mostly employed organellar genes, but these genes are generally inherited uniparentally, only partially reflecting the evolutionary history. In addition, chloroplast and mitochondrial genes are highly conserved, with limited numbers of phylogenetically informative characters. In contrast, nuclear genes are inherited biparentally and have relatively large numbers of informative sites, but only few nuclear genes have been utilized. In this work, sequences of five low-copy nuclear genes were obtained in 17 species from Brassicaceae and used for phylogenetic analyses with the Maximum-Parsimony, Maximum-Likelihood and Bayesian methods. Highly similar topologies were obtained using the five genes; in addition, compared with organellar genes, the nuclear genes had more phylogenetically informative sites and provided stronger supports. Specifically, the supporting values of all the nodes were 100% in MP trees using the five nuclear genes.Therefore,these five genes are excellent candidate marker genes for plant taxonomists who aim to resolve the relationships among low-level taxonomic hierarchies and might also be useful for DNA barcoding.