Chloroplast genomes and phylogenetic analysis of two species of Oedocladium (Oedogoniales, Chlorophyta)

Abstract

ABSTRACT The Oedogoniales comprises the genera Oedogonium, Oedocladium and Bulbochaete which include more than 600 described species. However, only two chloroplast genome sequences have been reported to date, and little is known about the evolutionary relationships between these genera or their infrageneric classification. This group is economically important in astaxanthin production and the energy sector. We examined four Oedocladium strains from different locations in China. One was identified as O. prescottii, and the morphology and molecular data for the other three strains suggested that they were O. carolinianum. Our chloroplast (cp) genome sequences of O. prescottii (FACHB-2452) and O. carolinianum (FACHB-2453) were compared with previously reported Oedogoniales cp genomes. The cp genome of O. carolinianum FACHB-2453 was of similar size, structure and composition to that of O. carolinianum UTEX LB 1686, apart from two missing group I introns in the genes psbA and psbD. O. prescottii showed more differences with regard to genome size, structure, number of genes and introns, and repeats than the other Oedogoniales cp genomes. The inverted repeats (IRs) region of the O. prescottii cp genome had a 10-kb contraction. Synteny analysis of the four cp genomes showed a high degree of syntenic conservation in general; however, some structural variation at genus level was observed in Oedocladium. In phylogenetic analyses of Oedocladium using sequences of 18S rDNA, ITS and 59 cp protein-coding genes, species were placed on two separate branches within the Oedogonium clade, indicating that Oedocladium is a paraphyletic group.