Abstract Detail

Mycological Section

Rehner, Stephen Austin [1], Kepler, Ryan M. [2].

Variation in ploidy in the ascomycete entomopathogens Metarhizium majus and M. guizhouense.

Understanding of ploidal variation in fungi lags behind that for plants and animals because cytogenetic tools are often unable to accurately resolve and size the typically small genomes of fungi. Variation in ploidal status is frequently associated with changes in phenotype, and sudden changes in chromosome number may promote rapid speciation and alter adaptive potential. With the advent of whole genome sequences for a broad diversity of fungal species it is now possible to develop taxon-specific genotyping tools that enable comprehensive assessment of ploidy across previously uncharacterized genomes. Here we present evidence based on nuclear DNA sequence, microsatellite polymorphisms and the configuration of the mating type locus to demonstrate independent origins of diploidy in Metarhizium majus and M. guizhouense, a sister species pair of soil-borne entomopathogens. A multilocus phylogeny revealed that each species lineage is phylogenetically complex and contains two or more distinct subclades. The majority of isolates in both species possess only a single sequence type or microsatellite allele at the 16 loci queried, indicating most individuals are haploid. However, the multilocus phylogeny also revealed single subclades within each species lineage whose members display more than one allele at multiple loci. After establishing single spore isolations to rule out mixed or heterokaryotic cultures, these same individuals displayed the same pattern of polymorphism as the parental cultures from which they originated, a finding consistent with a stable diploid genome structure. A PCR assay for diagnosis of mating type showed that haploid individuals were of a single mating type whereas presumed diploid isolates contained both MAT1-1 and MAT1-2 idiomorphs. Sequences spanning the intergenic spacer between APN2, which flanks the MAT locus, and the adjacent MAT1-1-3 and MAT1-2-1 idiomorphs differed in sequence, demonstrating that the different MAT loci in diploid strains are distinct from one another. Taken together, these data suggest that both diploid lineages are autopolyploids that likely arose by crosses between two closely related individuals of opposite mating type. The effect of this unique genomic arrangement on sexual reproduction remains to be determined.

1 - USDA-ARS, Systematic Mycology and Microbiology Laboratory, 10300 Baltimore Ave., Rm 213, Bldg 010A, BARC-W, Beltsville, MD, 20705, USA
2 - USDA-ARS, Systematic Mycology and Microbiology Laboratory, 10300 Baltimore Ave., Rm 213, Bldg 010A, BARC-W, Beltsville, MD, 20705, u

Keywords:
autopolyploidy
mating system
microsatellite
ascomycete.

Presentation Type: Oral Paper:Papers for Sections
Session: 12
Location: Salon 1/The Shaw Conference Centre
Date: Monday, July 27th, 2015
Time: 2:45 PM
Number: 12006
Abstract ID:1110
Candidate for Awards:None