title: Divergence of the mitochondrial genome structure in the apicomplexan parasites, Babesia and Theileria.
abstract: Mitochondrial (mt) genomes from diverse phylogenetic groups vary considerably in size, structure, and organization. The genus Plasmodium, causative agent of malaria, of the phylum Apicomplexa, has the smallest mt genome in the form of a circular and/or tandemly repeated linear element of 6 kb, encoding only three protein genes (cox1, cox3, and cob). The closely related genera Babesia and Theileria also have small mt genomes (6.6 kb) that are monomeric linear with an organization distinct from Plasmodium. To elucidate the structural divergence and evolution of mt genomes between Babesia/Theileria and Plasmodium, we determined five new sequences from Babesia bigemina, B. caballi, B. gibsoni, Theileria orientalis, and T. equi. Together with previously reported sequences of B. bovis, T. annulata, and T. parva, all eight Babesia and Theileria mt genomes are linear molecules with terminal inverted repeats (TIRs) on both ends containing three protein-coding genes (cox1, cox3, and cob) and six large subunit (LSU) ribosomal RNA (rRNA) gene fragments. The organization and transcriptional direction of protein-coding genes and the rRNA gene fragments were completely conserved in the four Babesia species. In contrast, notable variation occurred in the four Theileria species. Although the genome structures of T. annulata and T. parva were nearly identical to those of Babesia, an inversion in the 3-kb central region was found in T. orientalis. Moreover, the T. equi mt genome is the largest (8.2 kb) and most divergent with unusually long TIR sequences, in which cox3 and two LSU rRNA gene fragments are located. The T. equi mt genome showed little synteny to the other species. These results suggest that the Theileria mt genome is highly diverse with lineage-specific evolution in two Theileria species: genome inversion in T. orientalis and gene-embedded long TIR in T. equi.
authors.affiliation: Laboratory of Malariology, International Research Center of Infectious Diseases, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Hikosaka
authors.forename: Yoh-Ichi
authors.initials: Y
authors.lastname: Watanabe
authors.forename: Naotoshi
authors.initials: N
authors.lastname: Tsuji
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Kita
authors.forename: Hiroe
authors.initials: H
authors.lastname: Kishine
authors.forename: Nobuko
authors.initials: N
authors.lastname: Arisue
authors.forename: Nirianne Marie Q
authors.initials: NM
authors.lastname: Palacpac
authors.forename: Shin-Ichiro
authors.initials: S
authors.lastname: Kawazu
authors.forename: Hiromi
authors.initials: H
authors.lastname: Sawai
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Horii
authors.forename: Ikuo
authors.initials: I
authors.lastname: Igarashi
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Tanabe
mesh_terms: D000818:Animals; D001403:Babesia / Q000235:genetics*; D001483:Base Sequence; D017124:Conserved Sequence; D021901:DNA, Intergenic / Q000235:genetics; D014644:Genetic Variation; D054629:Genome, Mitochondrial / Q000235:genetics*; D018503:Genome, Protozoan / Q000235:genetics*; D016013:Likelihood Functions; D016366:Open Reading Frames / Q000235:genetics; D010271:Parasites / Q000235:genetics*; D010802:Phylogeny; D012689:Sequence Homology, Nucleic Acid; D016794:Theileria / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D021901:DNA, Intergenic