Molecular Phylogenetic Studies Of Oedogoniales (Chlorophyceae, Chlorophyta)

The Oedogoniales, has only the Oedogoniaceae, comprised of three genera Oedogonium, Oedocladium and Bulbochaete. Their fascinating and distinctive features such as the appearance ring formation during cell division, the extraordinarily conplex flagellar apparatus on their large zoospores and the various types of sexual production, are well known to phycologists set this order apart into a very unusual order of green algae.In this study, more species of Oedogoniales had been introduced by our wide range of sample collection and culture. The species analysed in this investigation had covered all the three genera of the Oedogoniales, and the numbers of species in each genus were over two to guarantee the feasibility of monophyletic analysis of the genus.The two nuclear genome noncoding sequences, 18S rDNA and 28S rDNA, have been analyzed respectively or united and phylogeny trees were constructed based on them using NJ, MP, ML and Bayesian methods. Results showed that the monophyletic clade Oeodgoniales was situated in a comparatively divergent position in the Chlorophyceae, but it was not robust and needed to be reassessed; the genus Oedocladium, as a separated clade, was clustered within the clade of Oedogonium; whereas the genus Bulbochaete was in a comparatively divergent position to the other two genera with a location basally in the Oeodgoniales; in addition, some strongly supported clades suggested that the relationships between Oedogonium taxa might be attributable to their sexual differentiation.In present investigation, we firstly obtained the chloroplast-encoded large subunit of the ribulose-1,5-bisphosphate carboxylase / oxygenase (rbcL) gene sequences. The results of the analyses based on these sequences make us believe that the Oedogoniales is better to be regarded as an unique order of the Chlorophyceae, and this order may considered to be a member of the earliest group of the class with some other filiform green algae. And within the Oedogoniales, the Bulbochaete is more complex than the other two genera, and the two branched genera (Bulbochaete and Oedocladium) are suggested to have been derived from an Oedogonium or Oedogonium-like ancestor.The relationship among the species of Oedogonium was discussed, focusing on ITS2 phylogeny analyzed combining with some morphological characteristics, and the CBC analyse was also performed. The results supported the Jao's hypothesis that the type of sexual differentiation should be the criterion for classification below the rank of genus Oedogonium from the view of molecular phylogeny. And furthermore, the evolution nexus from the monoecious to the dioecious nannandrous and then to the dioecious macrandrous taxa was supposed by this analyse.