以rDNA之ITS序列探討蝴蝶蘭屬植物之親緣關係

Abstract

17?18S-5.8S?25?28S rDNA為聚集型的重複性序列，每個重複單位包含轉錄區，ITS及IGS。其中ITS序列長度短，在物種間差異很大，且其兩側具高度保留性的轉錄區很容易擴增，因此常用於物種間親緣關係的分析。本實驗以P.aphrodite之18S和26S基因轉錄區設計一對專一性的引子，利用聚合酵素連鎖反應擴增28種蝴蝶蘭及1種朵麗蘭植物之ITS序列，分析種間的親緣關係。由con-NJ樹可將植物區分成6群，其中第2群包括P.stobartiana和P.parishii，第3群包括P.lued-pulehra、P.pallens和P.fasciata，皆與5S rDNA之IGS序列分析結果一致。另外P.amboinensis、P.venosa和P.violacea屬於同一群，與核型觀察及5S rDNA之IGS序列分析結果一致。而P. equestris、P.amabilis、P.aphrodite、P.sanderiana、P.stuarttana和P.schilleriana具小型染色體的蝴蝶蘭區分為三群，與5S rDNA之IGS序列分析的結果並不一致，可能是同一種植株因種源不同，導致ITS序列呈多型性所致。

l7?l8S-5.8S-25S rDNA are organized into clusters of tandem repeat with each repeat consisting of transcribed regions, two small ITS, and an IGS. Because the small size and the presence of highly conserved sequences flanking each of the two ITS make this region easy to amplify. The ITS sequences are variable among species and useful for phylogenetic analyses. In this study, ITS of 28 Phalaenopsis species were amplified by the polymerase chain reaction, cloned, and sequenced. Phylogenetic analysis of ITS consensus sequences could be divided into six groups. Among them the second group containing P.stobartiana and P.parishii and the third group containing P. lued-pulchra, P. pallens, and P. fasciata were consistent with IGS of 5S rDNA analysis. Similarly, P. amboinensis, P. venosa and P. violacea were also grouped together. Whereas P. equestris, P. mabilis, P. aphrodite, P. sanderiana, P. stuartiana, and P. schilleriana were divided into three groups, it might be the result of polymorphism in ITS sequences from different source of plants.