Basidiomycete Mating Type Genes and Pheromone Signaling

Abstract

2The genome sequences of the basidiomycete Agaricomycetes species Coprinopsis cinerea, Laccaria bicolor, Schizophyllum commune, Phanerochaete chrysosporium, and Postia placenta, as well as of Cryptococcus neoformans and Ustilago maydis, are now publicly available. Out of these fungi, C. cinerea, S. commune, and U. maydis, together with the budding yeast Saccharomyces cerevisiae, have been investigated for years genetically and molecularly for signaling in sexual reproduction. The comparison of the structure and organization of mating type genes in fungal genomes reveals an amazing conservation of genes regulating the sexual reproduction throughout the fungal kingdom. In agaricomycetes, two mating type loci, A, coding for homeodomain type transcription factors, and B, encoding a pheromone/receptor system, regulate the four typical mating interactions of tetrapolar species. Evidence for both A and B mating type genes can also be identified in basidiomycetes with bipolar systems, where only two mating interactions are seen. In some of these fungi, the B locus has lost its self/nonself discrimination ability and thus its specificity while retaining the other regulatory functions in development. In silico analyses now also permit the identification of putative components of the pheromone-dependent signaling pathways. Induction of these signaling cascades leads to development of dikaryotic mycelia, fruiting body formation, and meiotic spore production. In pheromone-dependent signaling, the role of heterotrimeric G proteins, components of a mitogen-activated protein kinase (MAPK) cascade, and cyclic AMP-dependent pathways can now be defined. Additionally, the pheromone-dependent signaling through monomeric, small GTPases potentially involved in creating the polarized cytoskeleton for reciprocal nuclear exchange and migration during mating is predicted. THE MATING SYSTEMS IN BASIDIOMYCETESThe typical life cycle of the higher basidiomycetes, presently classified as Agaricomycetes (Table 1) (34), consists of haploid, monokaryotic as well as dikaryotic stages, the latter of which prevails in nature. The monokaryotic mycelium contains nuclei of only one genetic type and is thus termed homokaryon. This mycelium, grown from haploid spores, in general contains one nucleus per cell (Fig. 1). The dikaryon is formed when genetically different homokaryons mate. In the saprotrophic agaricomycetes, the mushroom-forming species Schizophyllum commune and Coprinopsis cinerea (Table 1), mating is regulated by a tetrapolar system consisting of two unlinked genetic complexes, named A and B. The term tetrapolar reflects the fact that there are four possible mating interactions scored in matings between haploid strains derived from spores formed on the fruiting bodies of same parent dikaryon: a fully compatible interaction occurs when both A and B between the mates are of different specificities (Fig. 1), an incompatible interaction occurs when allelic specificities are all the same, and two semicompatible interactions occur when either A-o...

A Single Mating-Type Locus Composed of Homeodomain Genes Promotes Nuclear Migration and Heterokaryosis in the White-Rot Fungus Phanerochaete chrysosporium

“…More importantly, the very low levels of amino acid polymorphism among all of the pheromone receptors demonstrate that the population is essentially monomorphic for pheromone receptor proteins, suggesting that differences among strains are not due to allelism at these loci. Genome sequencing has likewise revealed that non-matingtype-specific pheromone receptors are common in Basidiomycetes (57,68,76), but it is also unclear what role they play in the sexual cycle, except in the case of C. neoformans receptor CPR2, where this non-mating-type-specific pheromone receptor plays a role in cell fusion and sporulation through the same G protein-coupled signaling cascade as the mating-type-specific pheromone receptors (32).…”

“…The MAT-B locus encodes small peptide pheromones and pheromone receptors that together control nuclear migration and the fusion of the clamp connections (11,65). As in the MAT-A proteins, only nonself interactions between pheromones and receptors stimulate nuclear migration through a G protein-coupled signaling pathway (21,27,58,68). Much less functional information is available for mating-type loci in bipolar species.…”

“…Genome sequencing has shown that the MAT gene homologues are found in every species examined (51)(52)(53), that most genomes have pheromone receptor-like genes that are not a part of MAT-B (56,68,76), and that there is conserved synteny near the MAT-A locus (35). The draft genome sequence of the P. chrysosporium homokaryotic strain RP-78 was no exception to these general findings, with a single genomic region encoding MAT-A homeodomain motif homologues and three additional genomic regions encoding putative pheromone receptors (53).…”

The Evolution of Sex: a Perspective from the Fungal Kingdom

“…There is a series of recent and classic reviews discussing the MAT locus in a wide variety of fungi from the fundamental model mating system Saccharomyces cerevisiae to the mating and virulence of human-pathogenic fungi and to the mushroom fungi (8,31,80,99,111,137,140,148,161,192,207,253).…”

Volatile sesquiterpenes from fungi: what are they good for?

“…These products are chemically very reactive, hence toxic on the one hand but instable on the other hand (Sterner et al 1985). Some of them are volatiles acting as repellents or kairomones (messengers for interspecies communication that just benefit the receiving organisms) (Raudaskoski and Kothe 2010;Bahn et al 2007 (Clericuzio et al 1999). The toxicity of this metabolite was tested against the brine shrimp Artemia salina.…”