An Overview of the Function and Maintenance of Sexual Reproduction in Dikaryotic Fungi

Abstract

Sexual reproduction likely evolved as protection from environmental stresses, specifically, to repair DNA damage, often via homologous recombination. In higher eukaryotes, meiosis and the production of gametes with allelic combinations different from parental type provides the side effect of increased genetic variation. In fungi it appears that while the maintenance of meiosis is paramount for success, outcrossing is not a driving force. In the subkingdom Dikarya, fungal members are characterized by existence of a dikaryon for extended stages within the life cycle. Such fungi possess functional or, in some cases, relictual, loci that govern sexual reproduction between members of their own species. All mating systems identified so far in the Dikarya employ a pheromone/receptor system for haploid organisms to recognize a compatible mating partner, although the paradigm in the Ascomycota, e.g., Saccharomyces cerevisiae, is that genes for the pheromone precursor and receptor are not found in the matingtype locus but rather are regulated by its products. Similarly, the mating systems in the Ascomycota are bipolar, with two non-allelic idiomorphs expressed in cells of opposite mating type. In contrast, for the Basidiomycota, both bipolar and tetrapolar mating systems have been well characterized; further, at least one locus directly encodes the pheromone precursor and the receptor for the pheromone of a different mating type, while a separate locus encodes proteins that may regulate the first locus and/or additional genes required for downstream events. Heterozygosity at both of two unlinked loci is required for cells to productively mate in tetrapolar systems, whereas in bipolar systems the two loci are tightly linked. Finally, a trade-off exists in wild fungal populations between sexual reproduction and the associated costs, with adverse conditions leading to mating. For fungal mammal pathogens, the products of sexual reproduction can be targets for the host immune system. The opposite appears true for phytopathogenic fungi, where mating and pathogenicity are inextricably linked. Here, we explore, compare, and contrast different strategies used among the Dikarya, both saprophytic and pathogenic fungi, and highlight differences between pathogens of mammals and pathogens of plants, providing context for selective pressures acting on this interesting group of fungi.

Dissecting the first phased dikaryotic genomes of the wheat rust pathogenPuccinia triticinareveals the mechanisms of somatic exchange in nature

“…Recently it has been suggested that the maintenance of mating type genes in dikaryotic fungi could have more profound meaning in multiple aspects of life style than just regulating sexual reproduction (33). Given the crucial functions and lack of understanding of these mating type genes in wheat rust fungi, we investigated the mating type genes across the phased genomes of the three Pt isolates.…”

“…One possible explanation could be that such a high diversity may be necessary for the successful heterodimerization of the HD genes in the SH process, which generates active transcription factors leading to a new developmental pathway (37). This pathway may involve biological processes crucial for a successful SH, such as DNA damage repair via homologous recombination, which has been suggested as the most plausible reason for maintaining the mating type genes in dikaryotic fungi without sexual reproduction (33).…”

Sexual Processes in Microbial Eukaryotes

“…The dikaryotic fungi (Ascomycetes and Basidiomycetes) include some of the most well-studied microbial eukaryotic species with respect to sexual reproduction. Wallen and Perlin [76] concluded in a 2018 review of the function and maintenance of sexual reproduction in the dikaryotic fungi that sexual reproduction, including its central feature of homologous recombination, evolved to repair DNA damages that arise particularly from environmental stresses. In the ascomycete yeast S. cerevisiae, DNA repair by homologous recombination during mitosis is well established.…”

Molecular Variation of the Phytopathogenic Fungus Sporisorium reilianum in Valle del Mezquital, Hidalgo

“…Likewise, in their respective hosts, each variety is able to resist the plants' attempts to eliminate infection, while, in the other species, the fungus succumbs to the plant's defense mechanisms. This selection phenomenon, probably does not favor variation within the mating type locus to reduce promiscuity between different species, though some studies sustain that it favors the maintenance of other specific genes that allow proliferation within the host, despite the plants' attempts to eliminate infection (Wallen and Perlin, 2018).…”