From two to one: Unipolar sexual reproduction

Abstract

While sexual reproduction is universal in eukaryotes, and shares conserved core features, the specific aspects of sexual reproduction can differ dramatically from species to species. This is also true in Fungi. Among fungal species, mating determination can vary from tetrapolar with more than a thousand different mating types, to bipolar with only two opposite mating types, and finally to unipolar without the need of a compatible mating partner for sexual reproduction. Cryptococcus neoformans is a human pathogenic fungus that belongs to the Basidiomycota. While C. neoformans has a well-defined bipolar mating system with two opposite mating types, MATa and MATα, it can also undergo homothallic unisexual reproduction from one single cell or between two cells of the same mating type. Recently, it was shown that, as in a-α bisexual reproduction, meiosis is also involved in α-α unisexual reproduction in C. neoformans. Briefly, recombination frequencies, the number of crossovers along chromosomes, as well as frequencies at which aneuploid and diploid progeny are produced, are all comparable between a-α bisexual and α-α unisexual reproduction. The plasticity observed in C. neoformans sexual reproduction highlights the extensive diversity in mating type determination, mating recognition, as well as modes of sexual reproduction across fungal species.

Heterothallism and potential hybridization events inferred for twenty-two yellow morel species

“…Reproductive modes of fungi are assumed to have a great influence on the evolutionary trajectory of their genomes (Burt 2000). In recent years, MAT genes have gained significant attention in evolutionary biology: on the one hand because of the general relationship between the evolution of reproductive genes and the reproductive modes of individuals (Paoletti et al 2006;Walters and Harrison 2008;Wik et al 2008), and on the other hand because MAT genes are known to be evolutionarily dynamic with high evolutionary rates (Gioti et al 2012;Martin et al 2013;Sun and Heitman 2015). Therefore, MAT gene sequences have often been used to study evolutionary trends of mating systems (Fraser et al 2007;Wik et al 2008) and population genetics (Zhan et al 2007;Groenewald et al 2007).…”

From dikaryon to diploid

“…a/a diploids of hybrid AD serotype are found in some geographical locations, whereas a/a diploids are not (Lin et al, 2009). The finding that aA/aD and aA/aA diploids are found in nature in diverse geographical locations, and that the majority are aA/aA lends support to the notion that same sex mating is widespread in nature (see Sun and Heitman, 2015, for in depth discussion of same sex mating in fungi). It was postulated that same sex mating may be an adaptation to the preponderance of a haploid isolates in the environment, or may be the source of the abundance of a cells (Lin et al, 2007).…”

Cryptococcus neoformans Mating and Genetic Crosses

“…Thus, Cryptococcus mating bears all of the hallmarks of sexual development in Basidiomycetes, making it an excellent model organism to study fungal sexual reproduction. In addition to mating between cells of opposite mating types, unisexual reproduction can also occur between MATα strains of C. deneoformans (Feretzaki & Heitman, 2013;Lin, Hull, & Heitman, 2005;Roth et al, 2018;Sun & Heitman, 2015;Sun et al, 2014).…”