Characterization of Euglenaformis gen. nov. and the chloroplast genome of Euglenaformis [Euglena] proxima (Euglenophyta)

Abstract

:Euglena proxima is a common, globally dispersed, and easily identified photosynthetic euglenoid. Previous phylogenetic analyses using nuclear-encoded small subunit (SSU) and large subunit (LSU) rRNA genes revealed that this taxon was paraphyletic with other Euglena species and was positioned as sister to all Euglenaceae. Despite this, authors were reluctant to remove this taxon from Euglena until additional data, or taxa pairing with E. proxima, were obtained because it created a monotypic genus. To clarify the taxonomy, the chloroplast genome of E. proxima was sequenced and compared with those of other photosynthetic euglenoids. Phylogenomic analyses were performed comparing 79 chloroplast-encoded genes from E. proxima with those found in seven photosynthetic euglenoids and three prasinophytes, the group from which the euglenoid chloroplast was probably derived. These analyses resulted in highly supported phylogenomic trees with topologies that were consistent with all previous phylogenetic analyses, i.e. they positioned E. proxima as sister to all of the Euglenaceae. In addition, a syntenic comparison was conducted between E. proxima and the chloroplast genomes of two Euglena taxa in order to determine their similarities. This analysis showed that the construction of the E. proxima chloroplast genome was very different from that of the two Euglena chloroplast genomes, which were extremely similar to each other. Based on these data, E. proxima was removed from Euglena, and a new genus, Euglenaformis, was erected to clarify the true relationship of this taxon to the rest of the photosynthetic euglenoids.