title: A plastid of probable green algal origin in Apicomplexan parasites.
abstract: Protozoan parasites of the phylum Apicomplexa contain three genetic elements: the nuclear and mitochondrial genomes characteristic of virtually all eukaryotic cells and a 35-kilobase circular extrachromosomal DNA. In situ hybridization techniques were used to localize the 35-kilobase DNA of Toxoplasma gondii to a discrete organelle surrounded by four membranes. Phylogenetic analysis of the tufA gene encoded by the 35-kilobase genomes of coccidians T. gondii and Eimeria tenella and the malaria parasite Plasmodium falciparum grouped this organellar genome with cyanobacteria and plastids, showing consistent clustering with green algal plastids. Taken together, these observations indicate that the Apicomplexa acquired a plastid by secondary endosymbiosis, probably from a green alga.
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: S
authors.initials: S
authors.lastname: Köhler
authors.forename: C F
authors.initials: CF
authors.lastname: Delwiche
authors.forename: P W
authors.initials: PW
authors.lastname: Denny
authors.forename: L G
authors.initials: LG
authors.lastname: Tilney
authors.forename: P
authors.initials: P
authors.lastname: Webster
authors.forename: R J
authors.initials: RJ
authors.lastname: Wilson
authors.forename: J D
authors.initials: JD
authors.lastname: Palmer
authors.forename: D S
authors.initials: DS
authors.lastname: Roos
mesh_terms: D000818:Animals; D016782:Apicomplexa / Q000235:genetics / Q000648:ultrastructure*; D000460:Chlorophyta / Q000235:genetics / Q000502:physiology / Q000648:ultrastructure*; D004270:DNA, Circular / Q000032:analysis*; D016054:DNA, Protozoan / Q000032:analysis*; D016786:Eimeria tenella / Q000235:genetics; D017403:In Situ Hybridization; D007425:Intracellular Membranes / Q000648:ultrastructure; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D010444:Peptide Elongation Factor Tu / Q000235:genetics; D010802:Phylogeny; D010963:Plasmodium falciparum / Q000235:genetics; D018087:Plastids / Q000235:genetics / Q000648:ultrastructure*; D013559:Symbiosis; D014122:Toxoplasma / Q000235:genetics / Q000502:physiology / Q000648:ultrastructure*
chemical_list: D004270:DNA, Circular; D016054:DNA, Protozoan; D010444:Peptide Elongation Factor Tu