title: Origins of a cyanobacterial 6-phosphogluconate dehydrogenase in plastid-lacking eukaryotes.
abstract: BACKGROUND
  Plastids have inherited their own genomes from a single cyanobacterial ancestor, but the majority of cyanobacterial genes, once retained in the ancestral plastid genome, have been lost or transferred into the eukaryotic host nuclear genome via endosymbiotic gene transfer. Although previous studies showed that cyanobacterial gnd genes, which encode 6-phosphogluconate dehydrogenase, are present in several plastid-lacking protists as well as primary and secondary plastid-containing phototrophic eukaryotes, the evolutionary paths of these genes remain elusive.
  
  
  RESULTS
  Here we show an extended phylogenetic analysis including novel gnd gene sequences from Excavata and Glaucophyta. Our analysis demonstrated the patchy distribution of the excavate genes in the gnd gene phylogeny. The Diplonema gene was related to cytosol-type genes in red algae and Opisthokonta, while heterolobosean genes occupied basal phylogenetic positions with plastid-type red algal genes within the monophyletic eukaryotic group that is sister to cyanobacterial genes. Statistical tests based on exhaustive maximum likelihood analyses strongly rejected that heterolobosean gnd genes were derived from a secondary plastid of green lineage. In addition, the cyanobacterial gnd genes from phototrophic and phagotrophic species in Euglenida were robustly monophyletic with Stramenopiles, and this monophyletic clade was moderately separated from those of red algae. These data suggest that these secondary phototrophic groups might have acquired the cyanobacterial genes independently of secondary endosymbioses.
  
  
  CONCLUSIONS
  We propose an evolutionary scenario in which plastid-lacking Excavata acquired cyanobacterial gnd genes via eukaryote-to-eukaryote lateral gene transfer or primary endosymbiotic gene transfer early in eukaryotic evolution, and then lost either their pre-existing or cyanobacterial gene.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan. maruyama@biol.s.u-tokyo.ac.jp
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Maruyama
authors.forename: Kazuharu
authors.initials: K
authors.lastname: Misawa
authors.forename: Mineo
authors.initials: M
authors.lastname: Iseki
authors.forename: Masakatsu
authors.initials: M
authors.lastname: Watanabe
authors.forename: Hisayoshi
authors.initials: H
authors.lastname: Nozaki
mesh_terms: D001499:Bayes Theorem; D000460:Chlorophyta / Q000201:enzymology / Q000235:genetics; D000458:Cyanobacteria / Q000201:enzymology* / Q000235:genetics*; D018076:DNA, Complementary; D019143:Evolution, Molecular; D015723:Gene Library; D022761:Gene Transfer, Horizontal; D016680:Genome, Bacterial; D018745:Genome, Plant; D016013:Likelihood Functions; D010734:Phosphogluconate Dehydrogenase / Q000235:genetics*; D010802:Phylogeny; D010944:Plants / Q000201:enzymology / Q000235:genetics; D018087:Plastids / Q000201:enzymology* / Q000235:genetics*; D016133:Polymerase Chain Reaction; D000461:Rhodophyta / Q000201:enzymology / Q000235:genetics
chemical_list: D018076:DNA, Complementary; D010734:Phosphogluconate Dehydrogenase