Out of western North America: Evolution of the Rhizopogon-Pseudotsuga symbiosis inferred by genome-scale sequence typing

Abstract

Abstract Mutual dependence and shared geographic distributions of ectomycorrhizal fungi and their hosts suggest that comigration has had an influential role in the evolution of the ectomycorrhizal symbiosis. To test the hypothesis of comigration of ectomycorrhizal symbionts we conducted a phylogeographic analysis of host specific ectomycorrhizal fungi in genus Rhizopogon sampled throughout the natural range of their Pseudotsuga (Douglas fir) hosts. Low coverage genome assemblies were sequenced for all Rhizopogon species-level clades and a novel data mining method, genome-scale sequence typing, was developed to produce a genome-scale phylogenetic dataset. Phylogenetic and phylogeographic analyses support a single evolutionary origin of the Rhizopogon-Pseudotsuga ectomycorrhizal symbiosis in coastal western North America with a single migration into Asia and two independent migrations east into the North American Intermountain West. Our results suggest that the Rhizopogon-Pseudotsuga ectomycorrhizal symbiosis predates species radiation in Pseudotsuga and that these genera have undergone processes of comigration and codiversification.