Molecular Phylogeny Of Haptophyta Emphasis On Isochrysis, Phaeocystis And Pavlova

Haptophyte are paid great attention by academic and governmental departments since they have rich nutrition and enable to cause red tides. At present, the taxonomy of haptophyte in China was based mainly on morphological characteristics, according to taxonomic standard of 1970s to 1980s. As there are some problems in the morphological taxonomy methods, the taxonomic system of haptophyte is controversy. For these reasons, 18S rRNA gene sequences of 8 Haptophyte, which affiliation to Isochrysis, Phaeocystis, Pavlova respectively, were determined, and phylogenetic relationships among some interrelated Haptophyte were studied.Firstly, four methods used to isolate DNA from Phaeocystis and Pavlova viridis were glass bead-extraction, CTAB-extraction, PVP-extraction and high salt-extraction DNA. Comparative studies showed that for Phaeocystis, which cells were rich secondary substances, glass bead-extraction DNA was method in choice; For Pavlova viridis, which had no cell wall, high salt-extraction DNA were better methods.Secondly, 18S rRNA gene sequences of 48 strain haptophyte algae, which including Isochrysis, Phaeocystis and Pavlova species were used to construt the phylogenetic tree with Skeletonema menzelii SZN-B83 as outgroup. Three major clades within haptophyte were identified: one clade embraces Phaeocystis; the second include Pavlova; the third includes members of the genera Emiliania, Prymnesium and Isochrysis. Some species of Isochrysis, Emiliania and ST2 were failed in Clade 2, within which Tahitian I. off. galbana, 3011, 8701, zhanjiangensis; and Isochrysis galbana UIO 102 clustered and ST2 was relatively isolated. In the clade Pavlova, every species clustered into indepentent clades. J1 was placed within the cluster of Pa. gyrans. Pa. viridis, Pa. virescens and Pa. lutheri clustered into one clade. The Phaeocystis is composed of five species: P. pouchetii, P. antarctica, P. globosa, P. cordata, P. jahnii. P2 was classified as P. globosa. Conclusions: 1, Haptophyta were clearly separated into two groups at the class level: Prymnesiophyceae and Pavlovophyceae. In Prymnesiophyceae, the establishment of Phaeocystales was holded. 2, ST2 might be a new species independent of I. galbana, even a new genera. Tahitian I. off. galbana, 3011, 8701, and zhanjiangensis all belonged toIsochrysis with close phylogenetic relationships to /. galbana. 3, P2 was P. globosa. 4, Jl was Pa. gyrans. Pa. viridis was closely related to Pa. virescens and Pa. lutheri.At last, the RNA secondary structure and gene sequences of P2 and P. antarctica psaA and psbA gene were comparatively analyzed. The results showed that both the RNA secondary structure of psaA and psbA genes could reflect the interspecific difference of Phaeocystis at a certain extent, and could provide some references to species identification of Phaeocystis.