ITS 假基因对栎属系统学研究的影响及其对分子系统学研究的启示*

核糖体rDNA ITS 是被子植物系统发育研究中应用最广泛的分子标记之一。以前人们认为同一物种
中的ITS 序列因致同进化而使不同拷贝高度一致, 在分子系统学研究中常以ITS1- 518S- ITS2 序列作为构建
系统进化树的基础。近年来, 在对一些被子植物的研究中发现这段序列在同一物种中具有多态性, 有些拷
贝中的518S 区不具编码功能, 人们把含有不具编码功能518S 区的ITS1-51 8S- ITS2 序列定义为ITS 假基因序
列, 它对同源基因致同进化的假设形成了新的挑战。在诸多应用ITS 序列重建系统进化关系的研究中, 栎
属系统学研究因ITS 假基因的发现而倍受关注。本文以栎属为例回顾了ITS 假基因的发现过程, 分析了其
对该属系统学研究的影响, 为分子生物学在植物系统进化研究中的应用提供一些新的参考。

Effect of ITS Pseudogene on the Phylogenetic Study of Quercus ( Fagaceae) and Its Revelation on the Plant Molecular Phylogenetics

Sequences of ITS in nrDNA is one of the widely used markers in angiosperm systematics. Many early reports of
ITS reg ion ( ITS 1, 518S and ITS 2) variation in flowering plants indicated that nrDNA arrays within individuals are homogeneous.
However, recent studies have discovered that individuals often contain potentially non-functional nrDNA copies
( pseudogenes) . These findings suggest that complete concerted evolution should not be assumed when embarking on phylogenetic
studies using nrDNA sequences. ITS pseudogene has been detected in the genus of Quercus L. and misled the
phylogenetic reconstruction, which made this genus frequently focused in the related studies. The authors take this genus
as an example to discuss the influence of the pseudogene on the phylogenetic study, conclude that combining application of
molecular evolution and classic taxonomy knowledge in plant systematics study may lead to more convincible results.