ITS2 and 18S rDNA sequence-structure phylogeny of Chlorella and allies (Chlorophyta, Trebouxiophyceae, Chlorellaceae)

Abstract

In the last decade, the evolutionary diversity of Chlorella and allies has been discussed in a huge number of publications using internal transcribed spacer 2 (ITS2) and/or 18S ribosomal RNA gene sequences to infer the phylogenies. However, sister-group relations between different genera classified within the Chlorellaceae remained provisional, due to a lack of bootstrap support. In this study, using more than four hundred sequences, a comprehensive phylogenetic portrait of Chlorella and allies is presented and discussed; sixty key taxa are reconsidered by an analysis using primary sequences and their individual secondary structures simultaneously in inferring neighbor-joining, maximum parsimony and maximum likelihood trees, an approach most recently reviewed, with increasing robustness and accuracy of reconstructed phylogenies. While neighbor-joining and maximum parsimony analyses failed in inferring a robust phylogenetic tree, the maximum likelihood tree (in particular on a concatenated data set) provides a supported phylogeny preceding any taxonomic discussion.