MOLECULAR-GENETICS OF MATING RECOGNITION IN BASIDIOMYCETE FUNGI

The recognition of compatible mating partners in the basidiomycete fun gi requires the coordinated activities of two gene complexes defined a s the mating-type genes. One complex encodes members of the homeobox f amily of transcription factors, which heterodimerize on mating to gene rate an active transcription regulator. The other complex encodes pept ide pheromones and 7-transmembrane receptors that permit intercellular signalling. Remarkably, a single species may have many thousands of c ross-compatible mating types because the mating-type genes are multial lelic. Different alleles of both sets of genes are necessary for matin g compatibility, and they trigger the initial stages of sexual develop ment-the formation of a specialized filamentous mycelium termed the di karyon, in which the haploid nuclei remain closely associated in each cell but do not fuse. Three species have been taken as models to descr ibe the molecular structure and organization of the mating-type loci a nd the genes sequestered within them: the pathogenic smut fungus Ustil ago maydis and the mushrooms Coprinus cinereus and Schizophyllum commu ne. Topics addressed in this review are the roles of the mating-type g ene products in regulating sexual development, the molecular basis for multiple mating types, and the molecular interactions that permit dif ferent allelic products of the mating type genes to be discriminated. Attention is drawn to the remarkable conservation in the mechanisms th at regulate sexual development in basidiomycetes and unicellular ascom ycete yeasts, Saccharomyces cerevisiae and Schizosaccharomyces pombe, a theme which is developed in the general conclusion to include the fi lamentous ascomycetes Neurospora crassa and Podospora anserina.