title: Recent transfer of an iron-regulated gene from the plastid to the nuclear genome in an oceanic diatom adapted to chronic iron limitation.
abstract: BACKGROUND
  Although the importance and widespread occurrence of iron limitation in the contemporary ocean is well documented, we still know relatively little about genetic adaptation of phytoplankton to these environments. Compared to its coastal relative Thalassiosira pseudonana, the oceanic diatom Thalassiosira oceanica is highly tolerant to iron limitation. The adaptation to low-iron conditions in T. oceanica has been attributed to a decrease in the photosynthetic components that are rich in iron. Genomic information on T. oceanica may shed light on the genetic basis of the physiological differences between the two species.
  
  
  RESULTS
  The complete 141790 bp sequence of the T. oceanica chloroplast genome [GenBank: GU323224], assembled from massively parallel pyrosequencing (454) shotgun reads, revealed that the petF gene encoding for ferredoxin, which is localized in the chloroplast genome in T. pseudonana and other diatoms, has been transferred to the nucleus in T. oceanica. The iron-sulfur protein ferredoxin, a key element of the chloroplast electron transport chain, can be replaced by the iron-free flavodoxin under iron-limited growth conditions thereby contributing to a reduction in the cellular iron requirements. From a comparison to the genomic context of the T. pseudonana petF gene, the T. oceanica ortholog can be traced back to its chloroplast origin. The coding potential of the T. oceanica chloroplast genome is comparable to that of T. pseudonana and Phaeodactylum tricornutum, though a novel expressed ORF appears in the genomic region that has been subjected to rearrangements linked to the petF gene transfer event.
  
  
  CONCLUSIONS
  The transfer of the petF from the cp to the nuclear genome in T. oceanica represents a major difference between the two closely related species. The ability of T. oceanica to tolerate iron limitation suggests that the transfer of petF from the chloroplast to the nuclear genome might have contributed to the ecological success of this species.
authors.affiliation: Leibniz Institute of Marine Sciences at Kiel University IFM-GEOMAR, Kiel, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Lommer
authors.forename: Alexandra-Sophie
authors.initials: AS
authors.lastname: Roy
authors.forename: Markus
authors.initials: M
authors.lastname: Schilhabel
authors.forename: Stefan
authors.initials: S
authors.lastname: Schreiber
authors.forename: Philip
authors.initials: P
authors.lastname: Rosenstiel
authors.forename: Julie
authors.initials: J
authors.lastname: LaRoche
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects / Q000235:genetics*; D000595:Amino Acid Sequence; D001483:Base Sequence; D002467:Cell Nucleus / Q000187:drug effects / Q000235:genetics*; D002874:Chromosome Mapping; D017377:Diatoms / Q000187:drug effects / Q000235:genetics*; D005288:Ferredoxins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D005796:Genes / Q000235:genetics*; D016678:Genome / Q000235:genetics*; D007501:Iron / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009792:Oceans and Seas; D010802:Phylogeny; D018087:Plastids / Q000187:drug effects / Q000235:genetics*; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism
chemical_list: D005288:Ferredoxins; D007501:Iron