A Comparative Study on Pheromone Communication between Schizophyllum species

Many fungal species are studied to understand pheromone and receptor interaction associated with mating behavior. An established genetic model for mating in higher fungi is heterothallic Schizophyllum commune . This fungus uses its pheromones to communicate compatibility among mates, typically leading to the production of haploid meiotic basidiospores. S. commune has thousands of mating types, as part of its tetrapolar mating system in which mating is determined by two unlinked complex genetic loci, one of which codes for both mating pheromones and receptors ( matB). Schizophyllum umbrinum is a fungal species which was described by Raper (1959) as a homothallic species but has not been studied in depth. S. umbrinum produces viable basidiospores, but has the means to bypass outcrossing. The studies described in this thesis were designed to examine components of a putative S. umbrinum matB locus and possible pheromone communication between the two Schizophyllum species. Two ways we explored S. umbrinum’s reproductive behavior was to look for evidence of functional pheromone genes and pheromones, and to search for variation among progeny and strains collected from different locations that might be indicative of more than one matB type and outcrossing. S. umbrinum matB noncoding regions were examined with PCR for variation among progeny of a wild-collected mushroom. There were no DNA length differences detected among 11 siblings for PCR covering 1.9 kb of amplified DNA and spaced over 11kb in the genome. Using Southern blot analysis, the whole matB coding and noncoding regions between putative pheromone genes suph1 and suph9 were examined. These results verified and expanded beyond the PCR assay. The results suggest that the mushroom that produced the 11 sibling strains was not produced by outcrossing that involved two different matB idiomorphs but was likely produced from a homothallic mating where no matB mating type idiomorphs exist. The conservation and similarities in amino acid sequences between the predicted mature pheromones of S. commune and S. umbrinum suggested possible function of the S. umbrinum pheromone genes products. Heterologous expression and activity were tested in baker’s yeast, S. cerevisiae, and S. umbrinum genes were also introduced into mushroom S. commune. In the yeast mating assay, successful communication between S. umbrinum pheromone SuPh3 and suph9 was demonstrated. In the S. commune mating assay, successful communication of S. umbrinum pheromones SuPh6, SuPh7, and suph9 with S. commune receptors in vivo was demonstrated. The ability to elicit signal transduction in both heterologous assay was observed by successful mating indication pheromone response. In conclusion, S. commune can express some S. umbrinum pheromone genes and process some of those gene products that resemble S. commune matB pheromones from their precursor to facilitate a response from S. commune receptors. Factors other than molecular compatibility may keep these signaling molecules in nature from interacting in these two sympatric species. To date, no evidence of self-activation of pheromone signaling within S. umbrinum has been discovered to explain the role of the pheromones in this homothallic species