Originally published as Genetics Published Articles Ahead of Print on February 3, 2006.

Genetics, Vol. 172, 1877-1891, March 2006, Copyright © 2006
doi:10.1534/genetics.105.051128

Evolution of the Bipolar Mating System of the Mushroom Coprinellus disseminatus From Its Tetrapolar Ancestors Involves Loss of Mating-Type-Specific Pheromone Receptor Function

Timothy Y. James^*,1, Prayook Srivilai, Ursula Kües and Rytas Vilgalys^*

^* Department of Biology, Duke University, Durham, North Carolina 27708 and Institute for Forest Botany, Georg-August-University, D-37077 Göttingen, Germany

¹ Corresponding author: Department of Biology, Duke University, Science Dr., Box 90338, Durham, NC 27708.
E-mail: tyj2{at}duke.edu

Mating incompatibility in mushroom fungi is controlled by the mating-type loci. In tetrapolar species, two unlinked mating-type loci exist (A and B), whereas in bipolar species there is only one locus. The A and B mating-type loci encode homeodomain transcription factors and pheromones and pheromone receptors, respectively. Most mushroom species have a tetrapolar mating system, but numerous transitions to bipolar mating systems have occurred. Here we determined the genes controlling mating type in the bipolar mushroom Coprinellus disseminatus. Through positional cloning and degenerate PCR, we sequenced both the transcription factor and pheromone receptor mating-type gene homologs from C. disseminatus. Only the transcription factor genes segregate with mating type, discounting the hypothesis of genetic linkage between the A and B mating-type loci as the causal origin of bipolar mating behavior. The mating-type locus of C. disseminatus is similar to the A mating-type locus of the model species Coprinopsis cinerea and encodes two tightly linked pairs of homeodomain transcription factor genes. When transformed into C. cinerea, the C. disseminatus A and B homologs elicited sexual reactions like native mating-type genes. Although mating type in C. disseminatus is controlled by only the transcription factor genes, cellular functions appear to be conserved for both groups of genes.

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