Mitochondrial group II introns in the raphidophycean flagellate Chattonella spp. suggest a diatom-to-Chattonella lateral group II intron transfer.
In the cytochrome c oxidase subunit I (cox1) gene of four raphidophycean flagellates Chattonella antiqua, C. marina, C. ovata, and C. minima we found two group II introns described here as Chattonella cox1-i1 and Chattonella cox1-i2 encoding an open reading frame (ORF) comprised of three domains: reverse transcriptase (RT), RNA maturase (Ma) and zinc finger (H-N-H) endonuclease domains. The secondary structures show both Chattonella cox1-i1 and Chattonella cox1-i2 belong to group IIA1, albeit the former possesses a group IIB-like secondary structural character in the epsilon' region of arm I. Our phylogenetic analysis inferred from RT domain sequences of the intronic ORF, comparison of the insertion sites, and the secondary structures of the introns suggests that Chattonella cox1-i1 likely shares an evolutionary origin with the group II introns inserted in cox1 genes of five phylogenetically diverged eukaryotes. In contrast, Chattonella cox1-i2 was suggested to bear a close evolutionary affinity to the group II introns found in diatom cox1 genes. The RT domain-based phylogeny shows a tree topology in which Chattonella cox1-i2 is nested in the diatom sequences suggesting that a diatom-to-Chattonella intron transfer has taken place. Finally, we found no intron in cox1 genes from deeper-branching raphidophyceans. Based on parsimonious discussion, Chattonella cox1-i1 and Chattonella cox1-i2 have invaded into the cox1 gene of an ancestral Chattonella cell after diverging from C. subsalsa.
Laboratory of Marine Microbiology, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan. ryoma.kamikawa@gmail.com
Ryoma
R
Kamikawa
Isao
I
Masuda
Mikihide
M
Demura
Kenichi
K
Oyama
Sadaaki
S
Yoshimatsu
Masanobu
M
Kawachi
Yoshihiko
Y
Sako
D000818:Animals; D004272:DNA, Mitochondrial / Q000737:chemistry / Q000235:genetics*; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics; D017377:Diatoms / Q000235:genetics*; D003576:Electron Transport Complex IV / Q000235:genetics*; D056890:Eukaryota / Q000235:genetics*; D019143:Evolution, Molecular; D022761:Gene Transfer, Horizontal; D007438:Introns; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000235:genetics; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid
D004272:DNA, Mitochondrial; D016054:DNA, Protozoan; D015800:Protozoan Proteins; D003576:Electron Transport Complex IV