10th Meeting of the International Society for Evolutionary Protistology (ISEP-10)
AUG 1994 Orsay, France. Invited presentation.
THE DIVERSIFICATION OF
MITOCHONDRIA IN PROTISTS: MEGASEQUENCING OF MICROGENOMES.
G.Burger*, C.J. O'Kelly, M.W. Gray, R.C. Cedergren,
M. Turmel, C. Lemieux, D. Sankoff, B. Golding, B.F. Lang.
(Presented by *.)
Organelle Genome Megasequencing Program, Canadian Institute for
Advanced Research, Departement de Biochimie, Universite de
Montreal, Montreal, Quebec H3C 3J7, Canada.
The principal objective of the Organelle Genome Megasequencing Program (OGMP) is
to reconstruct the phylogeny of protists, and the eukaryotes decended from them, by
analyzing complete sequences of mitochondrial (mt) genomes. The rationale for
sequencing complete genomes is that the historical record of one gene does not
necessarily reflect that of the entire genome. Moreover, complete mtDNA sequences
provide information about gene content and genome organization, and help to identify
new genes or genetic elements which may aid phylogenetic reconstructions. We use
ultrastructural indicators to select candidate protists for genome sequencing. The
candidates are then screened by phylogenetic analysis of their cox1 sequences that are
obtained via PCR. Protists are chosen for genome sequencing depending on a variety of
criteria such as the ease of bulk mtDNA purification, the size of the mt genome, the
tentative phylogenetic position as revealed by the cox1 sequences and the extent of
sequence derivation.
A number of mtDNAs have already been completely sequenced, including those of the
green alga Prototheca wickerhamii, the amoeba Acanthamoeba castellanii, the
chytridiomycetes Allomyces macrogynus and Spizellomyces punctatus, the oomycete
Phytophtora infestans, and the ciliate Tetrahymena pyriformis. The mtDNA sequences of
the rhodophyte Porphyra purpurea, the chrysophyte Ochromonas danica, the cryptomonad
Rhodomonas salina, the basidiomycete Schizophyllum commune, the zygomycete Rhizopus
stolonifer, and the bicosoecid Cafeteria roenbergensis, are nearly completed. Projects in
progress include the histionid Reclinomonas americana and the choanoflagellate Monosiga
sp.
Phylogenetic analyses based on deduced mt protein sequences parallel in general those
inferred from nuclear rRNA sequences. This is in agreement with (i) a monophyletic
origin of mitochondria; (ii) the view that mitochondria, unlike plastids, have not
participated in secondary endosymbioses, and (iii) an early divergence into major lineages
as reflected in the different shape of mt cristae (flattened, tubular, discoidal). Our analysis
also shows that the jakobid flagellates, whose nucleocytoplasmic features are ancient, are
likewise ancestral at the level of the mt genome.
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