Multiple Genes Encoding Pheromones and a Pheromone Receptor Define the Bβ1 Mating-Type Specificity in Schizophyllum commune

The genes defining multiple B mating types in the wood-rotting mushroom Schizophyllum commune are predicted to encode multiple pheromones and pheromone receptors. These genes are clustered in each of two recombinable and independently functioning loci, B alpha and B beta. A difference in specificity at either locus between a mated pair of individuals initiates an identical series of events in sexual morphogenesis. The B alpha 1 locus was recently found to contain genes predicted to encode three lipopeptide pheromones and a pheromone receptor with a seven-transmembrane domain. These gene products interact in hetero-specific pairs, the pheromone of one B alpha specificity with the receptor of any one of the other eight B alpha specificities, and are likely to activate a signaling cascade similar to that known for mating in Saccharomyces cerevisiae. We report here that the B beta 1 locus also contains at least three pheromone genes and one pheromone receptor gene, which function similarly to the genes in the B alpha 1 locus, but only within the series of B beta specificities. A comparison of the DNA sequences of the B alpha 1 and B beta 1 loci suggests that each arose from a common ancestral sequence, allowing us to speculate about the evolution of this unique series of regulatory genes.