Abstract Detail

Phylogenomics

Spies, Christoffel F. J. [1], Morisson, Hannah [2], Rintoul, Tara L. [1], Lévesque, C. André [1].

Phylogenomic approach to resolve the genus Pythium and the order Pythiales.

Debates about the systematic boundaries of the genus Pythium have existed since the group was defined but sequence based phylogenies have highlighted some old and several new classification issues. Eleven Pythium clades (A-K) were defined in the first comprehensive phylogeny of the genus 10 years ago. The new genus Phytopythium has now been assigned to clade K. Further taxonomic revision of the genus has been proposed, namely, Elongisporangium (clade H), Globisporangium (clades E-G, I and J) and Pythium sensu stricto (clades A-D). However, support for some critical nodes in the phylogenies supporting these proposed changes is weak and genera such as Lagena or Pythiogeton, closely related to these clades, were not sampled. Moreover, the position of some clades in both Pythium and oomycete phylogenies have proven to be variable depending on the markers and models used. The relationship of Clade H within Pythium is unresolved and the order Pythiales is not well defined within the oomycetes. Alternative sets of single-copy genes are needed to generate more accurate phylogenies than what traditional markers provide. From the sequenced genomes currently available within the oomycetes and other closely related Stramenopiles, 888 single-copy orthologous gene sequences have been identified from published genomes. To resolve the variable position of the Clade H in relation to the other nine clades within the genus Pythium, the genomes of two representative species, Pythium helicandrum and Pythium undulatum, and the closely related taxon Halophythophthora epistomium were sequenced. The majority of the identified 888 single-copy orthologous genes from the published genomes of interest were extracted from the assembled contigs. Phylogenetic analyses on concatenated data sets of these genes and new markers developed from them generated phylogenetic trees that cast new light on the problematic placement of Clade H in relation to the other clades within Pythium and the order-level classification of Pythium within the peronosporalean galaxy of the oomycetes.

1 - Agriculture and Agri-Food Canada, Central Experimental Farm, 960 Carling Avenue, Ottawa, ON, K1A 0C6, Canada
2 - University of Ottawa, Biology, 30 Marie Curie, Ottawa, ON, K1N 6N5, Canada

Keywords:
Oomycetes
Pythium
taxonomy
phytopathology.

Presentation Type: Oral Paper:Papers for Topics
Session: 73
Location: Salon 9/The Shaw Conference Centre
Date: Wednesday, July 29th, 2015
Time: 2:30 PM
Number: 73005
Abstract ID:1050
Candidate for Awards:None