title: A multigene phylogeny of Olpidium and its implications for early fungal evolution.
abstract: BACKGROUND
  From a common ancestor with animals, the earliest fungi inherited flagellated zoospores for dispersal in water. Terrestrial fungi lost all flagellated stages and reproduce instead with nonmotile spores. Olpidium virulentus (= Olpidium brassicae), a unicellular fungus parasitizing vascular plant root cells, seemed anomalous. Although Olpidium produces zoospores, in previous phylogenetic studies it appeared nested among the terrestrial fungi. Its position was based mainly on ribosomal gene sequences and was not strongly supported. Our goal in this study was to use amino acid sequences from four genes to reconstruct the branching order of the early-diverging fungi with particular emphasis on the position of Olpidium.
  
  
  RESULTS
  We concatenated sequences from the Ef-2, RPB1, RPB2 and actin loci for maximum likelihood and Bayesian analyses. In the resulting trees, Olpidium virulentus, O. bornovanus and non-flagellated terrestrial fungi formed a strongly supported clade. Topology tests rejected monophyly of the Olpidium species with any other clades of flagellated fungi. Placing Olpidium at the base of terrestrial fungi was also rejected. Within the terrestrial fungi, Olpidium formed a monophyletic group with the taxa traditionally classified in the phylum Zygomycota. Within Zygomycota, Mucoromycotina was robustly monophyletic. Although without bootstrap support, Monoblepharidomycetes, a small class of zoosporic fungi, diverged from the basal node in Fungi. The zoosporic phylum Blastocladiomycota appeared as the sister group to the terrestrial fungi plus Olpidium.
  
  
  CONCLUSIONS
  This study provides strong support for Olpidium as the closest living flagellated relative of the terrestrial fungi. Appearing nested among hyphal fungi, Olpidium's unicellular thallus may have been derived from ancestral hyphae. Early in their evolution, terrestrial hyphal fungi may have reproduced with zoospores.
authors.affiliation: Department of Botany, 3529-6270 University Boulevard, University of British Columbia, Vancouver, British Columbia, V6T 1Z4 Canada. ssekimoto@bama.ua.edu
authors.forename: Satoshi
authors.initials: S
authors.lastname: Sekimoto
authors.forename: D'Ann
authors.initials: D
authors.lastname: Rochon
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Long
authors.forename: Jaclyn M
authors.initials: JM
authors.lastname: Dee
authors.forename: Mary L
authors.initials: ML
authors.lastname: Berbee
mesh_terms: D008411:Chytridiomycota / Q000166:cytology / Q000235:genetics*; D004271:DNA, Fungal / Q000235:genetics / Q000302:isolation & purification; D019143:Evolution, Molecular; D005658:Fungi / Q000166:cytology / Q000235:genetics*; D010802:Phylogeny; D012331:RNA, Fungal / Q000235:genetics / Q000302:isolation & purification
chemical_list: D004271:DNA, Fungal; D012331:RNA, Fungal
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