Mating-type genes, pheromones and regulators of sexual development

In fungi, sexual reproduction takes place between partners that are morphologically indistinguishable and not differentiated into male and female. Compatible partners differ only in their mating type (MAT), and sexual reproduction is controlled by genes located in the mating-type locus. Mating-type genes encode transcription factors that act as master regulators of fertilization and sexual development and often control the genes for pheromones and pheromone receptors.
S. macrospora is self-fertile and needs no mating partner. We compared its mating-type locus with that of the heterothallic relative Neurospora crassa and showed that its mating-type genes are functional in a heterothallic ascomycete. Mating-type proteins of S. macrospora interact with each other, and gene expression in this homothallic fungus depends on the mating-type genes. A functional analysis of the MAT1-1-specific genes showed which of these regulators are essential for sexual development and which are not.
Although it is self-fertile, S. macrospora expresses two pheromone precursor genes and pheromone receptor genes. Pheromones and their receptors are required for proper sexual development, and an a-factor-like peptide pheromone and its interaction with its receptor were characterized in yeast. Further downstream, the MADS-box protein MCM1 interacts with a mating-type protein and is required for fruiting-body development; the STE12 homolog interacts with MCM1 and is required for ascosporogenesis; and the STE12-interacting protein SIP2 is involved in ascospore germination.
Knowledge of mating-type genes also uncovers hidden sexuality in fungi that were believed to be asexual. We found genomic evidence for mating abilities in the pathogen Aspergillus fumigatus and, together with collaboration partners, studied mating-type genes in the antibiotic producers Penicillium chrysogenum and Acremonium chrysogenum. On this basis a sexual cycle was induced in the penicillin producer P. chrysogenum and used for strain development, generating offspring with new combinations of traits relevant to penicillin production.
This topic connects directly to our current work. The pheromone response MAP kinase pathway is linked to the STRIPAK complex through the proteins DOC1 and DOC2, and the mating-type loci are the starting point of our project on genome evolution in homothallic and heterothallic Sordaria species.