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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 multicellular organisms such as fungi.

Definition

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Mating types are the microorganism equivalent to sex in higher organisms[1] and occur in isogamous 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.

Mating types are extensively studied in fungi. Among fungi, mating type is determined by chromosomal regions called mating-type loci. Furthermore, it is not as simple as "two different mating types can mate", but rather, a matter of combinatorics. As a simple example, most basidiomycete have a "tetrapolar heterothallism" mating system: there are two loci, and mating between two individuals is possible if the alleles on both loci are different. For example, if there are 3 alleles per locus, then there would be 9 mating types, each of which can mate with 4 other mating types.[3] By multiplicative combination, it generates a vast number of mating types.

Mechanism

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As an illustration, the model organism Coprinus cinereus has two mating-type loci called A and B. Both loci have 3 groups of genes. At the A locus are 6 homeodomain proteins arranged in 3 groups of 2 (HD1 and HD2), which arose by gene duplication. At the B locus, each of the 3 groups contain one pheromone G-protein-coupled receptor and usually two genes for pheromones.

The A locus ensures heterothallism through a specific interaction between HD1 and HD2 proteins. Within each group, a HD1 protein can only form a functional heterodimer with a HD2 protein from a different group, not with the HD2 protein from its own group. Functional heterodimers are necessary for a dikaryon-specific transcription factor, and its lack arrests the development process. They function redundantly, so it is only necessary for one of the three groups to be heterozygotic for the A locus to work.[4]

Similarly, the B locus ensures heterothallism through a specific interaction between pheromone receptors and pheromones. Each pheromone receptor is activated by pheromones from other groups, but not by the pheromone encoded by the same group. This means that a pheromone receptor can only trigger a signaling cascade when it binds to a pheromone from a different group, not when it binds to the pheromone from its own group. They also function redundantly.[4]

In both cases, the mechanism is based on a "self-incompatibility" principle, where the proteins or pheromones from the same group are incompatible with each other, but compatible with those from different groups.[5][6]

Similarly, the Schizophyllum commune has 2 gene groups (Aα, Aβ) for homeodomain proteins on the A locus, and 2 gene groups (Bα, Bβ) for pheromones and receptors on the B locus. Aα has 9 alleles, Aβ has 32, Bα has 9, and Bβ has 9. The two gene groups at the A locus function independently but redundantly, so only one group out of the two needs to be heterozygotic for it to work. Similarly for the two gene groups at the B locus. Thus, mating between two individuals succeeds if

 

Thus there are   mating types, each of which can mate with   other mating types.[7]

Occurrence

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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).[8] 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.[9] The corresponding mating types in yeast, a non-filamentous ascomycete, are referred to as MATa and MATα.[10]

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.[11]

Basidiomycetes can have thousands of different mating types.[12]

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.[13]

Evolution

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Main article: Evolution of sexual reproduction

Mating types likely predate anisogamy,[14] and sexes evolved directly from mating types or independently in some lineages.[15]

Studies on green algae have provided evidence for the evolutionary link between sexes and mating types.[16] In 2006 Japanese researchers found a gene in males of Pleodorina starrii that is an orthologue to a gene for a mating type in the Chlamydomonas reinhardtii.[17] In Volvocales, the plus mating type is the ancestor to female.[18]

In ciliates, multiple mating types evolved from binary mating types in several lineages.[19]: 75  As of 2019, genomic conflict has been considered the leading explanation for the evolution of two mating types.[20]

Secondary mating types evolved alongside simultaneous hermaphrodites in several lineages.[19]: 71 [clarification needed]

See also

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References

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  1. ^ a b "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. ^ Idnurm, Alexander; Hood, Michael E.; Johannesson, Hanna; Giraud, Tatiana (2015-12-01). "Contrasted patterns in mating-type chromosomes in fungi: Hotspots versus coldspots of recombination". Fungal Biology Reviews. Special Issue: Fungal sex and mushrooms – A credit to Lorna Casselton. 29 (3): 220–229. doi:10.1016/j.fbr.2015.06.001. ISSN 1749-4613. PMC 4680991.
  4. ^ a b Kamada, Takashi (May 2002). "Molecular genetics of sexual development in the mushroom Coprinus cinereus". BioEssays. 24 (5): 449–459. doi:10.1002/bies.10083. ISSN 0265-9247.
  5. ^ Riquelme, Meritxell; Challen, Michael P; Casselton, Lorna A; Brown, Andrew J (2005-07-01). "The Origin of Multiple B Mating Specificities in Coprinus cinereus". Genetics. 170 (3): 1105–1119. doi:10.1534/genetics.105.040774. ISSN 1943-2631. PMC 1451185. PMID 15879506.
  6. ^ Brown, Andrew J.; Casselton, Lorna A. (2001-07-01). "Mating in mushrooms: increasing the chances but prolonging the affair". Trends in Genetics. 17 (7): 393–400. doi:10.1016/S0168-9525(01)02343-5. ISSN 0168-9525.
  7. ^ Kothe, Erika (1996). "Tetrapolar fungal mating types: Sexes by the thousands". FEMS Microbiology Reviews. 18 (1): 65–87. doi:10.1016/0168-6445(96)00003-4. PMID 8672296.
  8. ^ 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.
  9. ^ 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.
  10. ^ Hanson, Sara J; Wolfe, Kenneth H (2017-05-01). "An Evolutionary Perspective on Yeast Mating-Type Switching". Genetics. 206 (1): 9–32. doi:10.1534/genetics.117.202036. ISSN 1943-2631. PMC 5419495. PMID 28476860.
  11. ^ 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.
  12. ^ Casselton LA (2002). "Mate recognition in fungi". Heredity. 88 (2): 142–147. doi:10.1038/sj.hdy.6800035. PMID 11932772.
  13. ^ 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
  14. ^ Andersson, Malte (1994-06-16). Sexual Selection. Princeton University Press. p. 4. ISBN 978-0-691-00057-2.
  15. ^ 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.
  16. ^ Sawada, Hitoshi; Inoue, Naokazu; Iwano, Megumi (2014). Sexual Reproduction in Animals and Plants. Springer. pp. 215–227. ISBN 978-4-431-54589-7.
  17. ^ 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. Bibcode:2006CBio...16R1018N. doi:10.1016/j.cub.2006.11.019. ISSN 0960-9822. PMID 17174904. S2CID 15748275.
  18. ^ 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.
  19. ^ a b Beukeboom, Leo W.; Perrin, Nicolas (2014). The Evolution of Sex Determination. Oxford University Press. ISBN 978-0-19-965714-8.
  20. ^ Hill, Geoffrey E. (2019-04-30). Mitonuclear Ecology. Oxford University Press. p. 115. ISBN 978-0-19-881825-0.
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