The Origin of Multiple Mating Types in the Model MushroomsCoprinopsis cinereaandSchizophyllum commune

Historically, Coprinopsis cinerea (C. lagopus sensu Buller, C. macrorhizus) and Schizophyllum commune were the first hymenomycete species shown to be heterothallic, and it is not surprising that studies on mating type have, until recently, focused on these two species. It was Hans Kniep who recognized that the matingtype genes were multiallelic and many different mating types existed in the population. Kniep's remarkably thorough studies, involving analyzing progeny from many generations of crosses, led him to note that some 1 to 2% of the progeny of sexual crosses in S. commune had new mating types, and he naturally attributed this to mutation. Haploid basidiospores germinate to give a self-sterile mycelium that is generally called a monokaryon because it has predominantly uninucleate cells. Mushrooms appear to be unique among fungi in having evolved multiple versions of their pheromones and receptors, and this has been driven by the need to increase the numbers of mating types. The genome sequence of C. cinerea reveals several clusters of genes of related function, suggesting that gene amplification has contributed to many aspects of the biology of this fungus. The majority of hymenomycetes are heterothallic, and it seems likely that as in ascomycetes, homothallic species were derived from heterothallic species. With the molecular and genomic tools we now have, exploring deeper into the study of the MAT loci enhances one's understanding of the importance of sex and its involvement in genome evolution.