Algae or Protozoa: Phylogenetic Position of Euglenophytes and Dinoflagellates as Inferred from Mitochondrial Sequences |
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Authors: | Yuji Inagaki Yasuko Hayashi-Ishimaru Megumi Ehara Ikuo Igarashi Takeshi Ohama |
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Institution: | (1) Biohistory Research Hall, 1-1 Murasaki-cho, Takatsuki, Osaka 569-11, Japan, JP;(2) Department of Biology, Faculty of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560, Japan, JP;(3) The Research Center for Protozoan Molecular Immunology, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080, Japan, JP |
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Abstract: | The chloroplasts of euglenophytes and dinoflagellates have been suggested to be the vestiges of endosymbiotic algae acquired
during the process of evolution. However, the evolutionary positions of these organisms are still inconclusive, and they have
been tentatively classified as both algae and protozoa. A representative gene of the mitochondrial genome, cytochrome oxidase
subunit I (coxI), was chosen and sequenced to clarify the phylogenetic positions of four dinoflagellates, two euglenophytes and one apicomplexan
protist. This is the first report of mitochondrial DNA sequences for dinoflagellates and euglenophytes. Our COXI tree shows clearly that dinoflagellates are closely linked to apicomplexan parasites but not with algae. Euglenophytes and
algae appear to be only remotely related, with euglenophytes sharing a possible evolutionary link with kinetoplastids. The
COXI tree is in general agreement with the tree based on the nuclear encoded small subunit of ribosomal RNA (SSU rRNA) genes,
but conflicts with that based on plastid genes. These results support the interpretation that chloroplasts present in euglenophytes
and dinoflagellates were captured from algae through endosymbioses, while their mitochondria were inherited from the host
cell. We suggest that dinoflagellates and euglenophytes were originally heterotrophic protists and that their chloroplasts
are remnants of endosymbiotic algae.
Received: 24 March 1997 / Accepted: 21 April 1997 |
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Keywords: | : Mitochondrial COXI gene — Dinoflagellata — Apicomplexa — Kinetoplastida — Euglenophyta — Endosymbiosis — Genetic code — Malarian circle |
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