Sheltered load in fungal mating-type chromosomes revealed by fitness experiments

bioRxiv (Cold Spring Harbor Laboratory), Journal Year: 2024, Volume and Issue: unknown

Published: Sept. 11, 2024

Abstract Sex chromosomes and mating-type can carry large regions with suppressed recombination. In these non-recombining regions, recessive deleterious mutations are expected to occur, as i) they predicted accumulate a result of lower efficacy selection, ii) may even pre-exist drive the evolution recombination suppression. Multiple genomic analyses have indirectly inferred presence in sex chromosomes, but direct experimental evidence remains scarce. Here, we performed fitness assays fungi megabase-large young around locus, using Schizothecium tetrasporum Podospora anserina species complexes, test whether heterokaryons (diploid-like, heterozygous at locus) exhibited advantage over homokaryons (haploid-like, single allele), terms spore germination dynamics or mycelium growth speed, under different conditions light temperature. We found faster compared one for P. 18°C, S. tritetrasporum 22°C light, also dark . These findings suggest sheltered load, i.e. state near highly homozygous otherwise. Leveraging on assets fungi, allowing cultivating separately haploid-like diploid-like life stages, our experiments provided rare load mating-compatibility loci, which is crucial understanding sex-related chromosome evolution.

Language: Английский

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Genetic differentiation in the MAT-proximal region is not sufficient for suppressing recombination in Podospora anserina

bioRxiv (Cold Spring Harbor Laboratory), Journal Year: 2024, Volume and Issue: unknown

Published: Dec. 7, 2024

ABSTRACT Recombination is advantageous over the long-term, as it allows efficient selection and purging deleterious mutations. Nevertheless, recombination suppression has repeatedly evolved in sex chromosomes mating-type chromosomes. The evolutionary causes for proximal mechanisms preventing crossing overs are still poorly understood. Several hypotheses have recently been suggested based on theoretical models, particular, that divergence could accumulate neutrally around a sex-determining region reduce rates, self-reinforcing process foster progressive extension of suppression. ascomycete fungus Podospora anserina an excellent model investigating these questions. A 0.8 Mb locus non-recombining, despite being collinear between two mating types. This mostly selfing, so strains highly homozygous, except non-recombining displays differentiation Here, we generated mutant to test hypothesis sequence alone responsible cessation. We replaced mat- idiomorph by mat+ idiomorph, obtain strain sexually compatible with reference isogenic this MAT -proximal region. Crosses showed was suppressed strains, indicating other than inversions or mere fungus. finding suggests selective likely acted suppressing recombination, neutral does not seem hold, at least ARTICLE SUMMARY In many organisms, observed locus. , within 800kb natural genome mating-types, displaying heterozygosity. To determine if heterozygosity can be lack were engineered isogenic, including inhibition persisted, cause Our study provides interesting insight molecular inhibition.

Language: Английский

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Million years old recombination suppression and balancing selection in a region linked to the mating-type locus in the invasive chestnut blight fungal pathogen Cryphonectria parasitica

bioRxiv (Cold Spring Harbor Laboratory), Journal Year: 2024, Volume and Issue: unknown

Published: March 30, 2024

Abstract Recombination suppression often evolves in sex chromosomes and around mating-type loci. In the invasive chestnut blight fungus Cryphonectria parasitica (Ascomycota), a genomic region was previously suggested to lack recombination be partially linked (MAT) locus based on analysis of few progenies. Using hundreds available C. genomes generating several new high-quality genome assemblies from native introduced range pathogen, we show that ca. 1.2 Mb proximal lacks worldwide. populations, this MAT-proximal displayed two highly differentiated haplotypes, were strongly associated mating types, but not completely. High-quality revealed an inversion one haplotypes footprints degeneration worldwide, being enriched gene disruptions, non-synonymous substitutions transposable elements both haplotypes. The divergence between estimated have occurred at least 1.5 million years ago segregate all continents, including range. High differentiation their occurrence different balanced frequencies within rearrangements altogether suggest ancient maintained by selection. MAT-Proximal carries multiple genes upregulated under virus infection or vegetative incompatibility reaction. This study sheds light case large non-recombining compatibility locus, balancing selection maintaining possibly involving deleterious mutations and/or host adaptation devastating tree pathogen.

Language: Английский

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