Mating-Type Locus Characterization and Allelic Diversity in Biosynthetic Genes for Putative Mycotoxins in the Fungal Pathogen 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 monocot weed in the Intermountain Western United States (Meyer et al., 2008). Since cheatgrass is an annual brome, successful control of it lies in the destruction of its seed bank.  In order to breed strains of P. semeniperda that are exceptionally effective at inhibiting cheatgrass seed germination, a selective breeding program must be developed based on an understanding of P. semeniperda polyketide domain and mating locus structures and reproductive strategies. Twelve genomes to date have been sequenced in order to reconstruct the multiple polyketide synthase domains which contain genes that underlie mycotoxin production and to characterize the mating type (MAT) locus. MAT locus characterization is particularly important in isolates that possess both mating-type genes, as characterization will determine whether the MAT genes are located within one nucleus or two genetically distinct nuclei. In regards to reproductive strategies, ascomycete fungi have developed diverse approaches to reproduction, including clonal, heterothallic, homothallic, and multinucleate systems. The heterothallic mating system consists of two self-infertile strains, each possessing either MAT1 or MAT2 at the mating-type locus and the homothallic mating system consists of self-fertile strains which possess both MAT1 and MAT2.  While P. semeniperda is an ascomycete haploid that predominantly reproduces asexually, it appears to have developed a unique mating system that involves both unikaryotic heterothallic individuals and dikaryotic (two genetically distinct nuclei within one organism) pseudohomothallic  individuals.