Genomic Analysis and Characterization of the Mating-Type Locus in the Fungal Pathogen Pyrenophora semeniperda

Pyrenophora semeniperda, is a generalist fungal pathogen that has shown promise as a potential biocontrol agent in the fight against cheatgrass (Bromus tectorum), a highly invasive monocot weed in the Intermountain Western United States.  In order to breed strains of P. semeniperda that are exceptionally effective at inhibiting B. tectorum seed germination, identification of isolate mating-type is necessary.  The P. semeniperda mating-type genes, MAT1 and MAT2, have been identified and sequenced for over 50 isolates to date. The P. semeniperda MAT1 and MAT2 genes are highly similar to the mating-type genes found in other Pyrenophora species. Our results indicate that while some isolates are heteromorphic and carry either MAT1 or MAT2, others are homomorphic and carry both genes.  Representation of each mating type varies from population to population. We developed a PCR protocol and used it to identify the mating type of 550 isolates across 15 populations. Populations are composed of variable ratios of mating types. Some have nearly equal ratios of all three possibilities- MAT1, MAT2, or MAT1 and MAT2, whereas other populations are dominated by one or two of the mating types. Structural analysis of the MAT locus has begun with the full genome sequencing of two P. semeniperda isolates (estimated genome size approx. 40 Mb) and will continue with the resequencing of 12 more full genomes representing all three heteromorphic and homomorphic mating types.