A LARGE PHEROMONE AND RECEPTOR GENE-COMPLEX DETERMINES MULTIPLE B-MATING-TYPE SPECIFICITIES IN COPRINUS-CINEREUS

Pheromone signaling plays an essential role in the mating and sexual d evelopment of mushroom fungi. Multiallelic genes encoding the peptide pheromones and their cognate 7-transmembrane helix (7-TM) receptors ar e sequestered in the B mating type locus. Here we describe the isolati on of the BG mating type locus of Coprinus cinereus. DNA sequencing an d transformation analysis identified nine genes encoding three 7-TM re ceptors and six peptide pheromone precursors embedded within 17 kb of mating type-specific sequence. The arrangement of the nine genes sugge sts that there may be three functionally independent subfamilies of ge nes each comprising two pheromone genes and one receptor gene. None of the nine BG genes showed detectable homology to corresponding B gene sequences in the genomic DNA from a B3 strain, and each of the B6 gene s independently alter B mating specificity when introduced into a B3 h ost str ain. However, only genes in two of the B6 groups were able to activate B-regulated development in a B42 host. Southern blot analysis showed that these genes failed to cross-hybridize to corresponding ge nes in the B42 host, whereas he three genes of the third subfamily, wh ich could not activate development in the B42 host, diet cross-hybridi ze. We conclude that cross-hybridization identifies the same alleles o f a particular subfamily of genes in different B loci and that B6 and B42 share alleles of one subfamily. There are an estimated 79 B mating specificities: we suggest that it is the different allele combination s of gene subfamilies that generate these large numbers.