Genetic Diversity and Mating-Type Locus Characterization in Pyrenophora semeniperda

Pyrenophora semeniperda is a naturally-occurring generalist fungal pathogen that has shown promise as a potential bio-control agent in the fight against Bromus tectorum (cheatgrass), a highly invasive weedy grass in the Intermountain Western United States. Since cheatgrass is an annual brome, successful control of it lies in the destruction of its seed bank. In order to improve or better utilize existing strains that have the potential to be exceptionally effective at killing cheatgrass seeds, P. semeniperda mating locus identities and reproductive strategies were characterized. This was accomplished through SSR- and MAT-typing of hundreds of strains and whole genome sequencing of twelve P. semeniperda strains using Illumina sequencing. While P. semeniperda is an ascomycete haploid that predominantly reproduces asexually, our genetic studies revealed that many isolates possess two MAT idiomorphs or alleles and two alleles at SSR loci. These findings suggest that hyphal fusion followed by nuclear transfer has created P. semeniperda populations that include dikaryotic pseudohomothallic individuals and both dikaryotic and unikaryotic heterothallic individuals. This unique reproductive system contributes to the genetic diversity of these populations and potentially provides researchers with an array of alleles to choose from for genes pertaining to mating strategies and toxin production.