科研之友
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摘要
The phylogeny of phagotrophic euglenids is widely based on nuclear small subunit ribosomal DNA (18S rDNA) sequence data, but most analyses suffer from weakness in statistical support regarding the "connecting backbone" between monophyletic clades. Moreover, the position of Entosiphon has remained unclear. Testing the 18S rDNA capability for a phylogeny of phagotrophic euglenids, we isolated sequences of Peranema sp. and Ploeotia edaphica and utilized secondary structure data as a prerequisite for recognition of homologous positions. We found a unique, clade-specific nucleotide substitution in the deduced 18S rDNA helix 44. Since our 18S rDNA phylogenies could only in part resolve positions of phagotrophic lineages, but did not verify that of Entosiphon, we investigated the phagotrophic key taxa Peranema trichophorum, Petalomonas cantuscygni, Ploeotia costata, and Entosiphon sulcatum ultrastructurally. Additionally, we explored the presence or absence of the euglenid reserve carbohydrate paramylon by specific staining with monoclonal anti-beta-1,3-glucan antibodies. Paramylon was found to be clearly present in P. trichophorum and E. sulcatum, but was absent in Pt. cantuscygni and Pl. costata. Combined results of our molecular, ultrastructural, and immunocytochemical investigations suggest that Entosiphon sulcatum is the sister taxon of a monophyletic euglenid crown clade, characterized by a helical pellicle, which we propose to rename. This phylogenetic affiliation is confirmed by a clade-specific primary absence of the unique nucleotide substitution in helix 44 and by the common presence of paramylon.
- 出版日期2017-9
