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I would have some related questions about the mating types of fungi.

  1. Does a single spore generate a mycelium possessing only one mating type? If it does not in general, do Ascomycota and Basidiomycota possess only one mating type per individual mycelium?

  2. Are homothallism and heterothallism properties of the individual mycelium or of the species? The definitions that I find in my book and on line confuse me. I understand that homothallism is the property of a mycelium (possessing only one mating type or can it possess many mating types in a similar way to hermaphrodite animals? cfr. question 1) that can mate with itself (if it can possess many mating types and it can mate with itself only by using gametes of different mating types, is it still homothallic?) and heterothallism is the property of a mycelium that is not homothallic, but I am not sure I understand, because I read of homothallic and heterothallic species too: is a homothallic species a species where at least some individual is homothallic, where all individuals are homothallic or something else?

  3. I am sure that mating type is a property characterising at least gametes, but is it a property of indiviual cells too? As an example, I know that it is necessary, among many species of fungi, for two gametes to belong to two different mating types in order to produce a zygote. Some fungi, as it is the rule among Basidiomycota, reproduce by somatogamy, i.e. the nuclei generating the zygote are from somatic cells, other than gametes. In such cases, are there species where it is necessary for the somatic cells of a homothallic mycelium to belong to a different type than the type with which they are undergoing plasmogamy? Thank you very much for any answer!

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Background:

Most fungi can reproduce sexually and asexually, and some even parasexually. Fungal reproduction is complicated!

Idiomorphs are at the exact same locus (like alleles) but produce a completely different protein rather than a variant of the protein.

Heterothalic - also called outbreeding: male and female reproductive structures are in different individuals. Partners have opposite mating-types with compatible MAT idiomorphs

Homothalic - also called inbreeding: male and female reproductive structures in the same individual. Partners have the same mating type but both MAT idiomorphs are present in the same genome and used in mating-type switching.

Heterothallic species are said to be homogenic incompatible, heterogenic incompatibility occurs when the offspring of a heterothallic cross between different strainss shows negative heterosis. There are forms of heterogenic incompatibility that appear to act only in the sexual phase.

Note that mating type and sex are not the same as sex is determined by mating structure and mating type may have no effect on sexual structure only on the nucleic content.

Answers:

1. I am not certain, but my understanding is that a haploid spore will generate a haploid mycelium of the same mating type. Note that things can get more complicated because you can have bifactorial incompatible mating types (e.g. two unlinked mating loci)

2. Homothallism and heterothallism are properties of the of the species

3. I am not entirely sure I understand the question here. In Basidiomycota (Club Fungi) Mycelia of + or - mating type will fuse to form a dikaryotic (two nuclei) mycelium for the majority of the life cycle. Only under unfavorable conditions will karyogamy (the fusing of the haploid nuclei) occur to form diploid hyphae and fruiting bodies where meiosis will take place to create haploid spores with mating types which will generate the new mycelia. Part of what makes the lifecycle here difficult is remembering that diploid somatic cells will have both mating types. (Life Cycle)

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