Molecular Genetics of Mating Recognition in Basidiomycete Fungi

Abstract

SUMMARY The recognition of compatible mating partners in the basidiomycete fungi requires the coordinated activities of two gene complexes defined as the mating-type genes. One complex encodes members of the homeobox family of transcription factors, which heterodimerize on mating to generate an active transcription regulator. The other complex encodes peptide pheromones and 7-transmembrane receptors that permit intercellular signalling. Remarkably, a single species may have many thousands of cross-compatible mating types because the mating-type genes are multiallelic. Different alleles of both sets of genes are necessary for mating compatibility, and they trigger the initial stages of sexual development—the formation of a specialized filamentous mycelium termed the dikaryon, in which the haploid nuclei remain closely associated in each cell but do not fuse. Three species have been taken as models to describe the molecular structure and organization of the mating-type loci and the genes sequestered within them: the pathogenic smut fungus Ustilago maydis and the mushrooms Coprinus cinereus and Schizophyllum commune. Topics addressed in this review are the roles of the mating-type gene products in regulating sexual development, the molecular basis for multiple mating types, and the molecular interactions that permit different allelic products of the mating type genes to be discriminated. Attention is drawn to the remarkable conservation in the mechanisms that regulate sexual development in basidiomycetes and unicellular ascomycete yeasts, Saccharomyces cerevisiae and Schizosaccharomyces pombe, a theme which is developed in the general conclusion to include the filamentous ascomycetes Neurospora crassa and Podospora anserina.

Septins enforce morphogenetic events during sexual reproduction and contribute to virulence of Cryptococcus neoformans

“…The mechanisms underlying clamp cell formation and subsequent fusion are largely unknown (Badalyan et al, 2004). Clamp cell formation and co-ordinated nuclear divisions are controlled by homeodomain transcription factors, whereas clamp cell fusion is dependent on pheromone and pheromone receptor genes (Casselton and Olesnicky, 1998), and the involvement of the clampless 1 protein (Clp1) has been decribed (Inada et al, 2001;Scherer et al, 2006;Ekena et al, 2008). We find that septins localize to the base of the clamp cell and close to the point of fusion between the clamp cell and the hypha,…”

“…4B). One of the landmark features of basidiomycetes is the clamp cell, which is essential for the proper segregation of nuclei in the dikaryotic hyphae (Casselton and Olesnicky, 1998). The clamp cell emerges from the hypha and grows as a bent protrusion that subsequently fuses with the same hypha following septum formation.…”

Profiling a killer, the development ofCryptococcus neoformans

“…Similar to other basidiomycetes, C. neoformans clamp cells are formed during each hyphal cell division and facilitate proper nuclear distribution and maintenance of the dikaryotic state (Casselton & Olesnicky, 1998) (Fig. 1).…”

“…The nucleus that is closer to the apex of the hypha divides, with the two resulting nuclei moving to the hyphal cell and the clamp cell, whereas the subapical nucleus divides within the hyphal cell, maintaining the dikaryotic state. In basidiomycetes, clamp cell formation and coordinated nuclear divisions are controlled by homeodomain transcription factors, but clamp cell fusion is dependent on pheromone and pheromone receptor genes (Casselton & Olesnicky, 1998). Coprinopsis cinerea clampless 1 protein (Clp1) participates in clamp formation (Inada et al, 2001) and U. maydis Clp1 is required for the formation of clamp-like structures (Scherer et al, 2006); however, further investigations are required to establish whether C. neoformans Clp1 acts during clamp cell formation (Ekena et al, 2008).…”

Cloning of the mating type loci from Pyrenopeziza brassicae reveals the presence of a novel mating type gene within a discomycete MAT 1‐2 locus encoding a putative metallothionein‐like protein

“…vegetative incompatibility (Beadle and Coonradt, 1944) and spore size dimorphism (Mathieson, 1952;Uhm and Fujii, 1983). Mating type loci have been studied in a number of fungi including members of both the ascomycetes and the basidiomycetes (Coppin et al, 1997;Casselton and Olesnicky, 1998). Molecular analysis of mating type organization within the ascomycetes has focused on three subgroups: the hemiascomycetes (Saccharomyces cerevisiae and Schizosaccharomyces pombe); the pyrenomycetes (Neurospora crassa, Podospora anserina and Magnaporthe grisea); and the loculoascomycetes (Cochliobolus heterostrophus) (Nelson, 1996;Coppin et al, 1997).…”