不同地理种群瓦氏马尾藻ITS序列特征及其系统进化分析

为研究不同地理种群瓦氏马尾藻ITS的序列变异,实验采用PCR扩增和序列测定方法,获得了3个不同地理种群15株瓦氏马尾藻的ITS全长序列,并进行序列分析。结果显示,15个个体共出现4种不同的ITS序列,它们相应的ITS1、5.8S、ITS2长度相同,均为762、158和507 bp,共有3个位点发生碱基变异。结合从GenBank中下载的马尾藻科3个属24种马尾藻的ITS序列,以羊栖菜属的羊栖菜,喇叭藻属的拟小叶喇叭藻和下延喇叭藻作为3个外群,采用邻位相连法构建分子系统进化树,结果显示,瓦氏马尾藻的ITS序列优先聚在一起然后以较高的置信度与南海马尾藻和球囊马尾藻聚为一支,在系统发生上显示出更近的亲缘关系。在选取的马尾藻中瓦氏马尾藻与南海马尾藻遗传距离最近为0.004,与拟小叶喇叭藻遗传距离最远为0.422。

Characterization and phylogenetic analysis of ITS sequences in three geographic populations of Sargassum vachellianum(Fucales,Phaeophyceae)

Sargassum vachellianum C.Agardh is native to China and mainly distributed in coastal waters of Zhejiang,Fujian,Guangdong and Hong Kong,China.It is important in maintaining the structure and function of littoral ecosystems and has been chosen as the main candidate for seaweed bed reconstruction by artificial breeding in China.Thus,to conserve and sustainably use this species,we should make genetic studies on it.As the traditional classification and phylogenetic relationships in Sargassum have been challenged by DNA phylogenies and the status of numerous species have been re-assessed,it is necessary to know whether the traditional taxonomy of S.vachellianum needs to be revised.However,there was no DNA markers have been reported in this important species.In this study,we cloned and sequenced ITS sequences of 15 S.vachellianum individuals from 3 different geographic populations.As a result,4 different ITS sequences were obtained.Sequence analysis revealed that the lengths of the four ITSs were all the same and their ITS1,5.8S and ITS2 were 762,158,and 507 bp,respectively.There were 3 mutations among the four ITS sequences,but no geographic population specific sites were found.The phylogenetic relationships among the four S.vachellianum ITSs and 24 GenBank ITS sequences from three genera of Sargassaceae were studied with sequences from Hizikia fusiformis,Turbinaria conoides and T.decurrens as three outgroups.The Neighbor-Joining phylogenetic tree constructed by MEGA 4.0 showed the four ITSs of S.vachellianum were clustered together first and then clustered with S.sp. and S.piluliferum,indicating a close genetic relationship corresponding to the smallest genetic distance(0.004)between S.vachellianum and S.sp.The greatest pairwise genetic distance(0.422)existed between S.vachellianum and T.conoides.