基于叶绿体rRNA ITS序列的兰科植物系统发育关系分析

叶绿体DNA(Chloroplast DNA,cpDNA)中的反向重复序列中的非编码区对于陆生植物的进化研究非常有指导意义,被越来越广泛的应用在不同的分类阶元的系统研究中.该研究在叶绿体rRNA ITS 序列的保守区设计引物,PCR扩增得到450 bp左右的叶绿体rRNA从4.5 S到5 S的片段,扩增产物直接测序,进而依据叶绿体rRNA ITS基因序列分析了兰科植物(Orchidaceae)的33个品种材料(12个兰属品种,14个兜兰属品种,7个石斛属品种)间的亲缘关系.通过最简约性分析产生的叶绿体rRNA ITS系统树表明,石斛属和兜兰属为两个自然类群,兰属可能为一多源组.兰属的碧玉兰位于系统树的基部,构成其余各种的姐妹支.兜兰属的白花兜兰、麻栗坡兜兰独立于属内其他种而自成一支.由于兰科植物叶绿体rRNA ITS序列变异率较低,最简约分析产生的分支得不到Bootstrap分析的高度支持,各亚属之间的关系也不明确.对兰科植物系统发育关系的研究尚需要更多的证据.

A Preliminary Analysis of Phylogenetic Relationships in Orchidaceae Based on cp rRNA ITS Sequence Data

Noncoding sequences from the inverted repeat region of chloroplast DNA appear suitable for phylogenetic study at different taxonomic levels.In this study,we developed PCR primers against highly conserved regions of the rRNA operon located and used these to amplify the region spanning from 4.5 S rRNA gene to 5 S rRNA gene,which is roughly 450 bp.The sequence of cp rRNA ITS regions of 33 orchidaceous(12 Cymbidiums,14 Paphiopedilums,and 7 Dendrobiums)were analyzed using PCR amplification and direct DNA sequencing.The phylogenetic trees generated from maximum parsimony analysis showed that Paphiopedilum and Dendrobium are monophyletic group while Cymbidium is polyphyletic with C.lowianum which is sister to the remainder species,P.emersonii and P.malipoense became the sister group to the remainder species within Paphiopedilum.However,because of the low substitution rate in the rRNA ITS region,some of the clades identified received relatively low support,subgenus delimitations were also not clear.Further study is needed for achieving a robust phylogeny of Orchidaceae.