title: Plastid genome sequences of Gymnochlora stellata, Lotharella vacuolata, and Partenskyella glossopodia reveal remarkable structural conservation among chlorarachniophyte species.
abstract: Chlorarachniophyte algae have complex plastids acquired by the uptake of a green algal endosymbiont, and this event is called secondary endosymbiosis. Interestingly, the plastids possess a relict endosymbiont nucleus, referred to as the nucleomorph, in the intermembrane space, and the nucleomorphs contain an extremely reduced and compacted genome in comparison with green algal nuclear genomes. Therefore, chlorarachniophyte plastids consist of two endosymbiotically derived genomes, i.e., the plastid and nucleomorph genomes. To date, complete nucleomorph genomes have been sequenced in four different species, whereas plastid genomes have been reported in only two species in chlorarachniophytes. To gain further insight into the evolution of endosymbiotic genomes in chlorarachniophytes, we newly sequenced the plastid genomes of three species, Gymnochlora stellata, Lotharella vacuolata, and Partenskyella glossopodia. Our findings reveal that chlorarachniophyte plastid genomes are highly conserved in size, gene content, and gene order among species, but their nucleomorph genomes are divergent in such features. Accordingly, the current architecture of the plastid genomes of chlorarachniophytes evolved in a common ancestor, and changed very little during their subsequent diversification. Furthermore, our phylogenetic analyses using multiple plastid genes suggest that chlorarachniophyte plastids are derived from a green algal lineage that is closely related to Bryopsidales in the Ulvophyceae group.
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Japan.
authors.forename: Shigekatsu
authors.initials: S
authors.lastname: Suzuki
authors.affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Japan.
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Hirakawa
authors.affiliation: Graduate School of Natural Science and Technology, Kanazawa University, Ishikawa, Japan.
authors.forename: Rumiko
authors.initials: R
authors.lastname: Kofuji
authors.affiliation: Center for Gene Research, Nagoya University, Aichi, Japan.
authors.forename: Mamoru
authors.initials: M
authors.lastname: Sugita
authors.affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Japan. ken@biol.tsukuba.ac.jp.
authors.forename: Ken-Ichiro
authors.initials: KI
authors.lastname: Ishida
mesh_terms: D001483:Base Sequence; D000460:Chlorophyta / Q000235:genetics*; D017124:Conserved Sequence / Q000235:genetics*; D054627:Genome, Plastid; D007438:Introns / Q000235:genetics; D016013:Likelihood Functions; D010802:Phylogeny; D013045:Species Specificity
keywords: Chlorarachniophyte; Endosymbiosis; Genome reduction; Nucleomorph; Plastid