Systematic study of the photosynthetic heterokonts based on molecular phylogenetic analysis

Abstract

Heterokont algae currently include 16 recognized classes. Until recently, relationships among these classes remained only partially resolved, in part because few studies included representatives from all the classes. We used a seven-gene (nuclear encoded SSU rRNA plastid encoded atpB, psaA, psaB, psbA, psbC, rbcL) dataset to analyze the relationships between 132 taxa representing all 16 classes. The analysis was the first to include representatives from other major photosynthetic lineages (Glaucophyta, Viridiplanteae, Rhodophyta, Cryptophyta and Haptophyta) as outgroup taxa. The phylogenetic tree recovered a strong monophyly of heterokont algae that were divided into 3 (or possibly 4) major clades. The Bacillariophyceae, Bolidophyceae, Dictyochophyceae and Pelagophyceae formed one clade. The Chrysophyceae, Eustigmatophyceae, Synchromophyceae and Synurophyceae formed a third clade. The Aurearenophyceae, Chrysomerophyceae, Phaeophyceae, Phaeothamniophyceae, Raphidophyceae, Schizocladiophyceae and Xanthophyceae formed another clade. The Pinguiophyceae could be recognized as a distinct, fourth clade. At various taxonomic levels, new lineages were discovered. The genus Chrysowaernella formed an independent lineage, and a new lineage of Pleurochloridella botrydiopsis and Phaeobotrys solitaria was found. Based on phylogenetic, morphological and biochemical data, we suggest a revision of the classification system for the puclear encoded SSU rRNA plastid encoded atpB, psaA, psaB, psbA, psbC, rbcL) dataset to analyze the relationships between 132 taxa representing all 16 classes. The analysis was the first to include representatives from other major photosynthetic lineages (Glaucophyta, Viridiplanteae, Rhodophyta, Cryptophyta and Haptophyta) as outgroup taxa. The phylogenetic tree recovered a strong monophyly of heterokont algae that were divided into 3 (or possibly 4) major clades. The Bacillariophyceae, Bolidophyceae, Dictyochophyceae and Pelagophyceae formed one clade. The Chrysophyceae, Eustigmatophyceae, Synchromophyceae and Synurophyceae formed a third clade. The Aurearenophyceae, Chrysomerophyceae, Phaeophyceae, Phaeothamniophyceae, Raphidophyceae, Schizocladiophyceae and Xanthophyceae formed another clade. The Pinguiophyceae could be recognized as a distinct, fourth clade. At various taxonomic levels, new lineages were discovered. The genus Chrysowaernella formed an independent lineage, and a new lineage of Pleurochloridella botrydiopsis and Phaeobotrys solitaria was found.