Studies on somatic recombination in dikaryons of Schizophyllum commune

The impact of ploidy on adaptation is a central issue in evolutionary biology. While many eukaryotic organisms exist as diploids, with two sets of gametic genomes residing in the same nucleus, most basidiomycete fungi exist as dikaryons in which the two genomes exist in separate nuclei that are physically paired and that divide in a coordinated manner during hyphal extension. To determine if haploid monokaryotic and dikaryotic mycelia adapt to novel environments under natural selection, we serially transferred replicate populations of each ploidy state on minimal medium for 18 months ‫000,31ف(‬ generations). Dikaryotic mycelia responded to selection with increases in growth rate, while haploid monokaryotic mycelia did not. To determine if the haploid components of the dikaryon adapt reciprocally to one another's presence over time, we recovered the intact haploid components of dikaryotic mycelia at different time points (without meiosis) and mated them with nuclei of different evolutionary histories. We found evidence for coadaptation between nuclei in one dikaryotic line, in which a dominant deleterious mutation in one nucleus was followed by a compensatory mutation in the other nucleus; the mutant nuclei that evolved together had the best overall fitness. In other lines, nuclei had equal or higher fitness when paired with nuclei of other histories, indicating a heterozygote advantage. To determine if genetic exchange occurs between the two nuclei of a dikaryon, we developed a 24-locus genotyping system based on single nucleotide polymorphisms to monitor somatic exchange. We observed genetic exchange and recombination between the nuclei of several different dikaryons, resulting in genotypic variation in these mitotic cell lineages.

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“…Each culture was markers (Papazian 1954;Crowe 1960;Parag 1962; serially transferred to a new petri dish every 2 weeks. Two 1964;Frankel 1979).…”

Section: Dikaryon-monokaryon Matingsmentioning

confidence: 99%

Dikaryons of the Basidiomycete Fungus Schizophyllum commune

Clark

Anderson

2004

Genetics

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“…In the latter case, the nuclei may have the same or different genotype at the mating type loci (Hibbett et al, 1994;Raper, 1966). Cell fusion and karyogamy are temporally and spatially separated in the life cycle of the majority of basidiomycete fungi, exemplified by Coprinopsis cinerea and Schizophyllum commune, which have long been used as model organisms for studies, among others, on mating type determination, fruiting body development, and somatic recombination (Casselton and Olesnicky, 1998;K€ ues, 2000;Papazian, 1954;Parag, 1962;Raper, 1966;Raudaskoski and Kothe, 2010;Stankis and Specht, 2007).…”

Section: Introductionmentioning

confidence: 98%

From dikaryon to diploid

Banuett¹

2015

Fungal Biology Reviews

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Dikaryon Diploid Haploidization Heterokaryon a b s t r a c t The dikaryon is the persistent vegetative phase of most basidiomycetes and arises by cell fusion of two haploids carrying different mating type alleles. The diplophase is restricted to a single cell (the basidium) where meiosis takes place. Cell fusion and karyogamy are thus temporally and spatially separated. The dikaryon is characterized by the presence in each cell of two genetically distinct nuclei in a 1:1 ratio and by clamp connections, structures involved in partitioning of the nuclei during their synchronous division. In Coprinopsis cinerea and Schizophyllum commune, with two mating type loci (A and B), heterokaryons with identical A alleles exhibit nuclear migration but no clamps, and those with identical B alleles have unfused clamps (pseudoclamps) and no nuclear migration. Armillaria species are exceptional among basidiomycetes because of their persistent vegetative diploid phase with no clamp connections. Cell fusion is followed immediately by karyogamy. Haploidization of the diploid nucleus may occur in the fruiting body, resulting in a new dikaryophaseediplophase. Diploids in Ustilago maydis were the first to be synthesized in any basidiomycete. They played a critical role in pioneering studies on DNA recombinationand repair. Subsequently diploids were generated in C. cinerea, S. commune, Microbotryum violaceum, and Cryptococcus neoformans. Dikaryons (or heterokaryons) and diploids of the same genotype exhibit phenotypic differences. The reason is not known but evidence indicates that gene expression differs when the same genetic information resides in two nuclei versus one nucleus in the same cell. Diploids in basidiomycete fungi are very stable by themselves but become unstable in 2N þ N or 2N þ 2N dikaryons. Instability results in haploidization (gradual loss of chromosomes) of the diploid nucleus. The mechanism that triggers this instability is not known.

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“…the occurrence of hyphal fusion between the confronting hyphae. A great deal has been done to unravel the mystery of the incompatibility factors (Raper, Baxter & Middleton, 1958;Raper, Baxter & Ellingboe, 1960;and Parag, 1962) and models have been proposed to pinpoint the sites of action and the mode of operation for each factor (Raper, Genetics of Sexuality in Higher Fungi, 1966, p. 213). Raper has presented a pattern wherein A and B factors control and regulate events, taking place after hyphal fusion, leading up to the establishment of a dikaryon and clamp-connexion formation.…”

Section: Introductionmentioning

confidence: 98%

Hyphal fusions in the wood-rotting fungusSchizophyllum commune: I. The effects of incompatibility factors

Ahmad

Miles

1970

Genet. Res.

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Effects of the incompatibility factors in Schizophyllum communeFries on the process of hyphal fusion are described. A role for the A incompatibility factor in hyphal fusion is indicated. Matings between strains with different mating types have higher fusion frequencies than matings between strains with the same mating types. Evidence is presented that the differences in fusion frequencies are not due to genetical factors other than mating types. When two strains of different mating types are grown in the same culture plate, but separated by a cellophane membrane, the strains are altered in some unexplained manner in such a way that even matings between strains of the same mating type have a higher fusion frequency than occurs in matings between compatible strains not so treated. Matings leading to the formation of common-B and dikaryotic mycelia have comparable fusion frequencies while those leading to the formation of common-A mycelia have a far lower frequency of fusions. It has been demonstrated that high fusion frequency is associated with heterozygosity at the A locus. It is suggested that a repression-derepression mechanism involving a cell wall degrading enzyme or enzymes may be involved in the regulation of hyphal fusion.

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Studies on somatic recombination in dikaryons of Schizophyllum commune

Cited by 27 publications

References 18 publications

Dikaryons of the Basidiomycete Fungus Schizophyllum commune

Dikaryons of the Basidiomycete Fungus Schizophyllum commune

From dikaryon to diploid

Hyphal fusions in the wood-rotting fungusSchizophyllum commune: I. The effects of incompatibility factors

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