Mating type

Mating types are the microorganism equivalent to sexes in multicellular lifeforms and are thought to be the ancestor to distinct sexes. They also occur in macro-organisms such as fungi.

Definition

Mating types are the microorganism equivalent to sex in higher organisms^[1] and occur in isogamous and anisogamous species.^[2] Depending on the group, different mating types are often referred to by numbers, letters, or simply "+" and "−" instead of "male" and "female", which refer to "sexes" or differences in size between gametes.^[1] Syngamy can only take place between gametes carrying different mating types.^{[citation needed]}

Occurrence

Reproduction by mating types is especially prevalent in fungi. Filamentous ascomycetes usually have two mating types referred to as "MAT1-1" and "MAT1-2", following the yeast mating-type locus (MAT).^[3] Under standard nomenclature, MAT1-1 (which may informally be called MAT1) encodes for a regulatory protein with an alpha box motif, while MAT1-2 (informally called MAT2) encodes for a protein with a high motility-group (HMG) DNA-binding motif, as in the yeast mating type MATα1.^[4] The corresponding mating types in yeast, a non-filamentous ascomycete, are referred to as MATa and MATα.^{[citation needed]}

Mating type genes in ascomycetes are called idiomorphs rather than alleles due to the uncertainty of the origin by common descent. The proteins they encode are transcription factors which regulate both the early and late stages of the sexual cycle. Heterothallic ascomycetes produce gametes, which present a single Mat idiomorph, and syngamy will only be possible between gametes carrying complementary mating types. On the other hand, homothallic ascomycetes produce gametes that can fuse with every other gamete in the population (including its own mitotic descendants) most often because each haploid contains the two alternate forms of the Mat locus in its genome.^[5]

Basidiomycetes can have thousands of different mating types.^[6]

In the ascomycete Neurospora crassa matings are restricted to interaction of strains of opposite mating type. This promotes some degree of outcrossing. Outcrossing, through complementation, could provide the benefit of masking recessive deleterious mutations in genes which function in the dikaryon and/or diploid stage of the life cycle.^[7]

Evolution

Main article: Evolution of sexual reproduction

Mating types likely predate anisogamy,^[8] and sexes evolved directly from mating types or independently in some lineages.^[9]

In 2006 Japanese researchers found a gene in males of P. starrii that’s an orthologue to a gene for a mating type in C. reinhardtii. Thus providing evidence for an evolutionary link between sexes and mating types.^[10]

Secondary mating types evolved alongside simultaneous hermaphrodites in several lineages.^{[11]: 71 [clarification needed]}

In Volvocales, the plus mating type is the ancestor to female.^[12] In ciliates multiple mating types evolved from binary mating types in several lineages.^[11]: 75 As of 2019, genomic conflict has been considered the leading explanation for the evolution of two mating types.^[13]

See also

• Mating in fungi
• Mating of yeast
• Mating-type locus
• Saccharomyces cerevisiae (a and α mating types)
• Schizophyllum commune (23,328 mating types)
• Tetrahymena (7 mating types)

References

1. "mating type". Oxford Reference. Retrieved 2021-08-26.
2. From Mating Types to Sexes. Bachtrog D, Mank JE, Peichel CL, Kirkpatrick M, Otto SP, et al. (2014) Sex Determination: Why So Many Ways of Doing It? PLoS Biol 12(7): e1001899. doi:10.1371/journal.pbio.1001899
3. Yoder, O.C.; Valent, Barbara; Chumley, Forrest (1986). "Genetic Nomenclature and Practice for Plant Pathogenic Fungi" (PDF). Phytopathology. 76 (4): 383–385. doi:10.1094/phyto-76-383. Retrieved 11 November 2015.
4. Turgeon, B.G.; Yoder, O.C. (2000). "Proposed Nomenclature for Mating Type Genes of Filamentous Ascomycetes". Fungal Genetics and Biology. 31 (1): 1–5. doi:10.1006/fgbi.2000.1227. PMID 11118130.
5. Giraud, T.; et al. (2008). "Mating system of the anther smut fungus Microbotryum violaceum: Selfing under heterothallism". Eukaryotic Cell. 7 (5): 765–775. doi:10.1128/ec.00440-07. PMC 2394975. PMID 18281603.
6. Casselton LA (2002). "Mate recognition in fungi". Heredity. 88 (2): 142–147. doi:10.1038/sj.hdy.6800035. PMID 11932772.
7. Bernstein H, Byerly HC, Hopf FA, Michod RE. Genetic damage, mutation, and the evolution of sex. Science. 1985 Sep 20;229(4719):1277-81. doi: 10.1126/science.3898363. PMID 3898363
8. Andersson, Malte (1994-06-16). Sexual Selection. Princeton University Press. p. 4. ISBN 978-0-691-00057-2.
9. Perrin, Nicolas (2012-04-06). "What Uses Are Mating Types? The "Developmental Switch" Model". Evolution. 66 (4): 947–956. doi:10.1111/j.1558-5646.2011.01562.x. PMID 22486681. S2CID 5798638.
10. Nozaki, Hisayoshi; Mori, Toshiyuki; Misumi, Osami; Matsunaga, Sachihiro; Kuroiwa, Tsuneyoshi (2006-12-19). "Males evolved from the dominant isogametic mating type". Current Biology. 16 (24): R1018–1020. doi:10.1016/j.cub.2006.11.019. ISSN 0960-9822. PMID 17174904. S2CID 15748275.
11. Beukeboom, Leo W.; Perrin, Nicolas (2014). The Evolution of Sex Determination. Oxford University Press. ISBN 978-0-19-965714-8.
12. Togashi, Tatsuya; Cox, Paul Alan (2011-04-14). The Evolution of Anisogamy: A Fundamental Phenomenon Underlying Sexual Selection. Cambridge University Press. pp. 1–15. ISBN 978-1-139-50082-1.
13. Hill, Geoffrey E. (2019-04-30). Mitonuclear Ecology. Oxford University Press. p. 115. ISBN 978-0-19-881825-0.