Long-term balancing selection in a white-rot fungi
Talk at VIII Biennial Conference of Society of Spanish Evolutionary Biology (SESBE). MATB. Previous studies have revealed that species of the genus Trichaptum (Hymenochaetales, Basidiomycota) possess a tetrapolar mating system, with multiple inferred alleles for MATA and MATB. We characterized the chromosomal location of MAT loci, the molecular structure of MAT regions and their allelic richness. We found multiple MAT alleles segregating in both multiple Trichaptum specimens and non-Trichaptum species. Phylogenetic analyses and various nucleotide statistics suggested that long-term balancing selection have generated trans-species polymorphisms. Mating sequences were classified in different allelic classes based on an identity threshold of higher than 86%. The observed alleles could potentially generate 14,560 different mating types. The inferred allelic information mirrored the outcome of in vitro crosses, thus allowing us to estimate the degree of allelic divergence needed for successful mating. Even with the high amount of divergence, key amino acids in functional domains are conserved. We conclude that the genetic diversity of mating in Trichaptum loci is due to long-term balancing selection that likely promote sexual outcrossing, with limited recombination and duplication activity. Our large number of sequenced specimens highlighted the importance of sequencing multiple individuals from different species to clarify the mechanisms generating diversity and the evolutionary forces maintaining them.
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Long-term balancing selection in a white-rot fungi
- 1. Long-term balancing selection in a white-rot fungi David Peris Department of Biosciences, UiO Department of Health, VIU VIII Biennial Conference SESBE 2nd February 2022 @DPerisN @FungiaLab
- 2. Trichaptum species belong to the Basidiomycota phyla Gaya et al 2018
- 3. Northern distribution of the white-rot fungi, Trichaptum
- 4. Trichaptum has a tetrapolar system Burnett 1965 Raper 1966 Macrae 1967 Ryvarden 1972 Magasi 1976
- 5. In Trichaptum multiple alleles define multiple mating types Burnett 1965 Raper 1966 Macrae 1967 Ryvarden 1972 Magasi 1976
- 7. Running hypotheses (H1): The tetrapolar character of Trichaptum must be determined by two unlinked loci.
- 8. Running hypotheses (H1): The tetrapolar character of Trichaptum must be determined by two unlinked loci. (H2): The high number of alleles is maintained by balancing selection
- 9. Main questions: Q1 How are the mating loci structured in three Trichaptum species?
- 10. How are the mating loci structured in three Trichaptum species? Peris et al 2021 Under review Main questions: Q1
- 11. How are the mating loci structured in three Trichaptum species? n=1 n=1 Main questions: Q1
- 12. Diversity of mating alleles complicates the search
- 13. MATA contains two pairs of homeodomain genes (two complexes)
- 14. MATB contains 4 pheromone receptor and 2 pheromone precursor genes
- 15. Main questions: Q2 What are the levels of molecular diversity at Trichaptum MAT regions?
- 16. Low nucleotide conservation in mating related genes
- 17. Low nucleotide conservation in two pheromone receptors and pheromone precursors
- 18. A pair of the complex interacts with the other pair from a different allele Trichaptum spp. aHD2.9 aHD1.22 aHD.4 Homeodomain 1 (HD1) Homeodomain 2 (HD2) Casselton and Olesnicky 1998 Chr 2 Basidiomycetes MATA-122 aHD2.12 aHD1.5 bHD2.7 bHD.8 aHD.30 bHD.5 bHD2.5 bHD1.7 Chr 2 MATA-21 MATA alpha beta Tetrapolar
- 19. Pairs from the same chromosome cannot interact Trichaptum spp. aHD2.9 aHD1.22 aHD.4 Homeodomain 1 (HD1) Homeodomain 2 (HD2) Casselton and Olesnicky 1998 Chr 2 Basidiomycetes MATA-122 aHD2.12 aHD1.5 bHD2.7 bHD.8 aHD.30 bHD.5 bHD2.5 bHD1.7 Chr 2 MATA-21 alpha beta MATA Tetrapolar
- 20. Pairs from different complexes does not interact Trichaptum spp. aHD2.9 aHD1.22 aHD.4 Homeodomain 1 (HD1) Homeodomain 2 (HD2) Casselton and Olesnicky 1998 Chr 2 Basidiomycetes MATA-122 aHD2.12 aHD1.5 bHD2.7 bHD.8 aHD.30 bHD.5 bHD2.5 bHD1.7 Chr 2 MATA-21 alpha beta MATA Tetrapolar
- 21. Trichaptum spp. Casselton and Olesnicky 1998 Basidiomycetes A pheromone interacts with the pheromone receptor from a different allele Pheromone receptor (STE3) Pheromone precursor (Ph) Chr 9 MATB-7 P/R3.2.1 Chr 9 MATB-11 STE3.2.1 STE3.4.12 STE3.2.1 STE3.4.8 P/R3.2.1 P/R3.4.12 P/R3.4.8 Ph3.2.1 Ph3.2.1 Ph3.4.12 Ph3.4.8 P/R 3.2 P/R 3.4 MATB Tetrapolar
- 22. Main questions: Q3 Are Trichaptum mating-related genes under balancing selection?
- 23. Most flanking genes agree with the species tree
- 24. Mating related genes show evidence of trans-species polymorphisms
- 25. Nucleotide statistics supports balancing selection MATB Region
- 26. Main questions: Q4 How long have Trichaptum mating-related genes been segregating?
- 27. bHD proteins are older than aHD and were segregating for long time
- 29. Trichaptum life cycle: inbreeding reduced to 25% Monokaryons (n) Dikaryons (n+n) Diploid (2n) < karyogamy Haploid spores < meiosis (n) Haploid spores (n) Mating type 12 MATA-21 MATB-7 Mating type 26 MATA-122 MATB-11 Plasmogamy A21B7 A21B21 A27B21 A27B7
- 30. 50% chance of inbreeding Homeodomain 1 Homeodomain 2 HMG-domain transcription activator Hsueh & Heitman 2008 Jackson et al 2013 MAT/MATa Diploid (2n) a a Tetrad Spore Saccharomyces cerevisiae 2 1 a1 Chr III MAT MATa Bipolar
- 31. Take home messages Trichaptum species are tetrapolar due to the presence of unlinked MATA and MATB loci.
- 32. Take home messages Trichaptum species are tetrapolar due to the presence of unlinked MATA and MATB loci. Trichaptum mating genes is an example of long-term balancing selection generating trans- species polymorphisms.
- 33. Take home messages Trichaptum species are tetrapolar due to the presence of unlinked MATA and MATB loci. Trichaptum mating genes is an example of long-term balancing selection generating trans- species polymorphisms. We inferred 17,550 Trichaptum mating types that reduced inbreeding and facilitate outbreeding
- 34. Take home messages Trichaptum species are tetrapolar due to the presence of unlinked MATA and MATB loci. Trichaptum mating genes is an example of long-term balancing selection generating trans- species polymorphisms. We inferred 17,550 Trichaptum mating types that reduced inbreeding and facilitate outbreeding A new fantastic organism to study the evolution of sex in fungi
- 35. Inger Skrede Dabao Sun Lu Vilde Bruhn Kinneberg Ine-Susanne Methlie Malin Dahl Ingvild Myhre Ekeberg Håvard Kauserud UiO@Speciomics Thank you Timothy James Collaborations Acknowledgements Sebastián Ramos Onsins (CRAG) Georgina May