运用nrDNAITS数据研究角叉菜属(Chondrus)在红藻门中的系统进化地位

PHYLOGENETIC STATUS OF CHONDRUS STACKHOUSE IN RHODOPHYTA BASED ON nrDNA ITS DATA

测定了角叉菜属(Chondrus)5个代表种的核糖体DNA内转录间隔区(ITS)及5.8SrDNA基因序列。结果表明,角叉菜属ITS区(含ITS1、5.8SrDNA和ITS2)序列长度范围为704—714bp,G+C含量为44.6%—45.7%,变异位点69个,信息位点16个;其中,ITS1和ITS2的长度范围分别为147—149bp和398—404bp。5.8SrDNA长度为158bp,没有变异和信息位点。由MEGA3构建的系统进化树(ME和MP)显示:在进化尺度上,真红藻纲的松节藻科(Rhodomelaceae)与红毛菜纲(Bangiophyceae)亲缘关系较近。在真红藻纲内,杉藻目(Gigartinales)的进化地位相对较高,其次是海膜科(Halymeniaceae)、石花菜科(Gelidiaceae)、红叶藻科(Delesseriaceae)和粉枝藻科(Liagoraceae)等,而松节藻科进化地位相对较低。在杉藻目内,杉藻科(Gigartinaceae)和胶黏藻科(Dumontiaceae)进化关系密切,而形态学特征相似的角叉菜和马泽藻(Mazzaella)亲缘关系非常近。

Chondrus Stackhouse is a perennial red seaweed with alternate phases of gametophyte and tetrasporophyte; over-harvesting and environmental pollution have hugely reduced the population resource and resulted in shortage of a constant and reliable supply. For this genus the classification and systematics are puzzled for variable forms, habitats and phenotypic plasticity. Meanwhile, as a representative family in Rhodophyta, Gigartinaceae are one of the important taxa for understanding the origin and evolution of red algae because of its lower position in cladograms of Rhodophyta phylogeny based on molecular data. However, both the phylogenetic affinity within Gigartinales and the evolution status of Gigartinaceae in Rhodophyta remain uncertain. In this study, the internal transcribed spacer （ITS） region of nuclear ribosomal DNA and 5.8S rDNA gene were sequenced for five representative species of Chondrus, C. ocellatus, C. armatus, C. yendoi, C. pinnulatus and C. crispus, for assessing the phylogenetic relationships in Rhodophyta on molecular level, in addition to reevaluation of the evolutionary status of Chondrus. The results indicate that the ITS region ranges from 704 to 714bp and G＋C content varies from 44.6% to 45.7%, including 69 variable sites and 16 informative sites; and the length variation is 1.4%. ITS1 （147—149bp） with 16 variable sites and four informative sites is shorter than ITS2 （398—404bp） with 53 variable sites and 12 informative sites; and 5.8S rDNA gene has conservative 158bp, with no variable and informative sites. Phylogenetic analyses using minimum-evolution and maximum-parsimony methods with MEGA3 show that Rhodomelaceae in Florideophyceae is closely related to Bangiophyceae at evolutional level. In Florideophyceae, Gigartinales has the relatively highest evolutional level, then Halymeniaceae, Gelidiaceae, Delesseriaceae and Liagoraceae, and Rhodomelaceae the lowest. In Gigartinales, Gigartinaceae and Dumontiaceae have a close relationship, while Chondrus and Mazzaella, which are difficult to discriminate in morphology, formed a fairly compact clade. The low divergence among Chondrus species is justified considering its more recent origin, and also suggests that ITS sequence would provide a promising method for molecular phylogenetic analysis, and to reconstruct the phylogeny within Rhodophyta on order and family levels.