title: Phylogenomics demonstrates that breviate flagellates are related to opisthokonts and apusomonads.
abstract: Most eukaryotic lineages belong to one of a few major groups. However, several protistan lineages have not yet been robustly placed in any of these groups. Both the breviates and apusomonads are two such lineages that appear to be related to the Amoebozoa and Opisthokonta (i.e. the 'unikonts' or Amorphea); however, their precise phylogenetic positions remain unclear. Here, we describe a novel microaerophilic breviate, Pygsuia biforma gen. nov. sp. nov., isolated from a hypoxic estuarine sediment. Ultrastructurally, this species resembles the breviate genera Breviata and Subulatomonas but has two cell morphologies, adherent and swimming. Phylogenetic analyses of the small sub-unit rRNA gene show that Pygsuia is the sister to the other breviates. We constructed a 159-protein supermatrix, including orthologues identified in RNA-seq data from Pygsuia. Phylogenomic analyses of this dataset show that breviates, apusomonads and Opisthokonta form a strongly supported major eukaryotic grouping we name the Obazoa. Although some phylogenetic methods disagree, the balance of evidence suggests that the breviate lineage forms the deepest branch within Obazoa. We also found transcripts encoding a nearly complete integrin adhesome from Pygsuia, indicating that this protein complex involved in metazoan multicellularity may have evolved earlier in eukaryote evolution than previously thought.
authors.affiliation: Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada. protist@live.com
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Brown
authors.forename: Susan C
authors.initials: SC
authors.lastname: Sharpe
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Silberman
authors.forename: Aaron A
authors.initials: AA
authors.lastname: Heiss
authors.forename: B Franz
authors.initials: BF
authors.lastname: Lang
authors.forename: Alastair G B
authors.initials: AG
authors.lastname: Simpson
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Roger
mesh_terms: D017753:Ecosystem; D063366:Estuaries; D056890:Eukaryota / Q000145:classification* / Q000235:genetics* / Q000648:ultrastructure; D019143:Evolution, Molecular; D020459:Genes, rRNA; D019015:Geologic Sediments; D008969:Molecular Sequence Data; D010802:Phylogeny; D016053:RNA, Protozoan / Q000235:genetics / Q000378:metabolism; D017423:Sequence Analysis, RNA
chemical_list: D016053:RNA, Protozoan
keywords: animal–fungal clade; eukaryote evolution; integrin; mitochondria; protist