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Meunier C, Darolti I, Reimegård J, Mank JE, Johannesson H. Nuclear-specific gene expression in heterokaryons of the filamentous ascomycete Neurospora tetrasperma. Proc Biol Sci 2022; 289:20220971. [PMID: 35946150 PMCID: PMC9363985 DOI: 10.1098/rspb.2022.0971] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Heterokaryosis is a system in which genetically distinct nuclei coexist within the same cytoplasm. While heterokaryosis dominates the life cycle of many fungal species, the transcriptomic changes associated with the transition from homokaryosis to heterokaryosis is not well understood. Here, we analyse gene expression profiles of homokaryons and heterokaryons from three phylogenetically and reproductively isolated lineages of the filamentous ascomycete Neurospora tetrasperma. We show that heterokaryons are transcriptionally distinct from homokaryons in the sexual stage of development, but not in the vegetative stage, suggesting that the phenotypic switch to fertility in heterokaryons is associated with major changes in gene expression. Heterokaryon expression is predominantly defined by additive effects of its two nuclear components. Furthermore, allele-specific expression analysis of heterokaryons with varying nuclear ratios show patterns of expression ratios strongly dependent on nuclear ratios in the vegetative stage. By contrast, in the sexual stage, strong deviations of expression ratios indicate a co-regulation of nuclear gene expression in all three lineages. Taken together, our results show two levels of expression control: additive effects suggest a nuclear level of expression, whereas co-regulation of gene expression indicate a heterokaryon level of control.
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Affiliation(s)
- Cécile Meunier
- Department ECOBIO, UMR CNRS 6553, Université Rennes 1, Rennes, France
| | - Iulia Darolti
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, Canada
| | - Johan Reimegård
- Department of Cell and Molecular Biology, National Bioinformatics Infrastructure Sweden, Science for Life Laboratory, Uppsala University, Uppsala, Sweden
| | - Judith E. Mank
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, Canada,Centre for Ecology and Conservation, University of Exeter, Penryn Campus, UK
| | - Hanna Johannesson
- Department of Organismal Biology, Uppsala University, Uppsala, Sweden,The Royal Swedish Academy of Sciences and Department of Ecology, Environment and Plant Sciences, Stockholm University, SE-106 91 Stockholm, Sweden
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Gladieux P, De Bellis F, Hann-Soden C, Svedberg J, Johannesson H, Taylor JW. Neurospora from Natural Populations: Population Genomics Insights into the Life History of a Model Microbial Eukaryote. Methods Mol Biol 2021; 2090:313-336. [PMID: 31975173 DOI: 10.1007/978-1-0716-0199-0_13] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
The ascomycete filamentous fungus Neurospora crassa played a historic role in experimental biology and became a model system for genetic research. Stimulated by a systematic effort to collect wild strains initiated by Stanford geneticist David Perkins, the genus Neurospora has also become a basic model for the study of evolutionary processes, speciation, and population biology. In this chapter, we will first trace the history that brought Neurospora into the era of population genomics. We will then cover the major contributions of population genomic investigations using Neurospora to our understanding of microbial biogeography and speciation, and review recent work using population genomics and genome-wide association mapping that illustrates the unique potential of Neurospora as a model for identifying the genetic basis of (potentially adaptive) phenotypes in filamentous fungi. The advent of population genomics has contributed to firmly establish Neurospora as a complete model system and we hope our review will entice biologists to include Neurospora in their research.
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Affiliation(s)
- Pierre Gladieux
- UMR BGPI, Univ Montpellier, CIRAD, INRA, Montpellier SupAgro, Montpellier, France.
| | - Fabien De Bellis
- UMR AGAP, Univ Montpellier, CIRAD, INRA, Montpellier SupAgro, Montpellier, France
| | - Christopher Hann-Soden
- Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, CA, USA
| | - Jesper Svedberg
- Department of Organismal Biology, Uppsala University, Uppsala, Sweden
| | - Hanna Johannesson
- Department of Organismal Biology, Uppsala University, Uppsala, Sweden
| | - John W Taylor
- Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, CA, USA
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Meunier C, Hosseini S, Heidari N, Maryush Z, Johannesson H. Multilevel Selection in the Filamentous Ascomycete Neurospora tetrasperma. Am Nat 2018. [DOI: 10.1086/695803] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Corcoran P, Anderson JL, Jacobson DJ, Sun Y, Ni P, Lascoux M, Johannesson H. Introgression maintains the genetic integrity of the mating-type determining chromosome of the fungus Neurospora tetrasperma. Genome Res 2016; 26:486-98. [PMID: 26893460 PMCID: PMC4817772 DOI: 10.1101/gr.197244.115] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2015] [Accepted: 02/16/2016] [Indexed: 01/01/2023]
Abstract
Genome evolution is driven by a complex interplay of factors, including selection, recombination, and introgression. The regions determining sexual identity are particularly dynamic parts of eukaryotic genomes that are prone to molecular degeneration associated with suppressed recombination. In the fungus Neurospora tetrasperma, it has been proposed that this molecular degeneration is counteracted by the introgression of nondegenerated DNA from closely related species. In this study, we used comparative and population genomic analyses of 92 genomes from eight phylogenetically and reproductively isolated lineages of N. tetrasperma, and its three closest relatives, to investigate the factors shaping the evolutionary history of the genomes.We found that suppressed recombination extends across at least 6 Mbp (∼ 63%) of the mating-type (mat) chromosome in N. tetrasperma and is associated with decreased genetic diversity, which is likely the result primarily of selection at linked sites. Furthermore, analyses of molecular evolution revealed an increased mutational load in this region, relative to recombining regions. However, comparative genomic and phylogenetic analyses indicate that the mat chromosomes are temporarily regenerated via introgression from sister species; six of eight lineages show introgression into one of their mat chromosomes, with multiple Neurospora species acting as donors. The introgressed tracts have been fixed within lineages, suggesting that they confer an adaptive advantage in natural populations, and our analyses support the presence of selective sweeps in at least one lineage. Thus, these data strongly support the previously hypothesized role of introgression as a mechanism for the maintenance of mating-type determining chromosomal regions.
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Affiliation(s)
- Pádraic Corcoran
- Department of Organismal Biology, Uppsala University, 752 36 Uppsala, Sweden; Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, United Kingdom
| | - Jennifer L Anderson
- Department of Organismal Biology, Uppsala University, 752 36 Uppsala, Sweden
| | - David J Jacobson
- Department of Organismal Biology, Uppsala University, 752 36 Uppsala, Sweden
| | - Yu Sun
- Department of Cell and Molecular Biology, Uppsala University, 752 36 Uppsala, Sweden
| | | | - Martin Lascoux
- Department of Ecology and Genetics, Science for Life Laboratory, Uppsala University, 752 36 Uppsala, Sweden
| | - Hanna Johannesson
- Department of Organismal Biology, Uppsala University, 752 36 Uppsala, Sweden
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Grognet P, Silar P. Maintaining heterokaryosis in pseudo-homothallic fungi. Commun Integr Biol 2015; 8:e994382. [PMID: 26479494 PMCID: PMC4594319 DOI: 10.4161/19420889.2014.994382] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2014] [Accepted: 11/06/2014] [Indexed: 01/09/2023] Open
Abstract
Among all the strategies displayed by fungi to reproduce and propagate, some species have adopted a peculiar behavior called pseudo-homothallism. Pseudo-homothallic fungi are true heterothallics, i.e., they need 2 genetically-compatible partners to mate, but they produce self-fertile mycelium in which the 2 different nuclei carrying the compatible mating types are present. This lifestyle not only enables the fungus to reproduce without finding a compatible partner, but also to cross with any mate it may encounter. However, to be fully functional, pseudo-homothallism requires maintaining heterokaryosis at every stage of the life cycle. We recently showed that neither the structure of the mating-type locus nor hybrid-enhancing effect due to the presence of the 2 mating types accounts for the maintenance of heterokaryosis in the pseudo-homothallic fungus P. anserina. In this addendum, we summarize the mechanisms creating heterokaryosis in P. anserina and 2 other well-known pseudo-homothallic fungi, Neurospora tetrasperma and Agaricus bisporus. We also discuss mechanisms potentially involved in maintaining heterokaryosis in these 3 species.
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Affiliation(s)
- Pierre Grognet
- Univ Paris Diderot; Sorbonne Paris Cité; Institut des Energies de Demain ; Paris, France
| | - Philippe Silar
- Univ Paris Diderot; Sorbonne Paris Cité; Institut des Energies de Demain ; Paris, France
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Neurospora Heterokaryons with Complementary Duplications and Deficiencies in Their Constituent Nuclei Provide an Approach to Identify Nucleus-Limited Genes. G3-GENES GENOMES GENETICS 2015; 5:1263-72. [PMID: 25897010 PMCID: PMC4478554 DOI: 10.1534/g3.115.017616] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Introgression is the transfer of genes or genomic regions from one species into another via hybridization and back-crosses. We have introgressed four translocations (EB4, IBj5, UK14-1, and B362i) from Neurospora crassa into N. tetrasperma. This enabled us to construct two general types of heterokaryons with mat-A and mat-a nuclei of different genotypes: one type is [T + N] (with one translocation nucleus and one normal sequence nucleus), and the other is [Dp + Df] (with one nucleus carrying a duplication of the translocation region and the other being deleted for the translocation region). Self-crossing these heterokaryons again produced [T + N] and [Dp + Df] progeny. From conidia (vegetative spores) produced by the heterokaryotic mycelia, we obtained self-fertile (heterokaryotic) and self-sterile (homokaryotic) derivative strains. [T + N] heterokaryons produced homokaryotic conidial derivatives of both mating types, but [Dp + Df] heterokaryons produced viable conidial homokaryons of only the mating type of the Dp nucleus. All four [T + N] heterokaryons and three [Dp + Df] heterokaryons produced both self-sterile and self-fertile conidial derivatives, but the [Dp(B362i) + Df(B362i)] heterokaryons produced only self-sterile ones. Conceivably, the Df(B362i) nuclei may be deleted for a nucleus-limited gene required for efficient mitosis or nuclear division, and whose deficit is not complemented by the neighboring Dp(B362i) nuclei. A cross involving Dp(EB4) showed repeat-induced point mutation (RIP). Because RIP can occur in self-crosses of [Dp + Df] but not [T + N] heterokaryons, RIP alteration of a translocated segment would depend on the relative numbers of [Dp + Df] vs. [T + N] ancestors.
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Samils N, Oliva J, Johannesson H. Nuclear interactions in a heterokaryon: insight from the model Neurospora tetrasperma. Proc Biol Sci 2015; 281:rspb.2014.0084. [PMID: 24850920 DOI: 10.1098/rspb.2014.0084] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A heterokaryon is a tissue type composed of cells containing genetically different nuclei. Although heterokaryosis is commonly found in nature, an understanding of the evolutionary implications of this phenomenon is largely lacking. Here, we use the filamentous ascomycete Neurospora tetrasperma to study the interplay between nuclei in heterokaryons across vegetative and sexual developmental stages. This fungus harbours nuclei of two opposite mating types (mat A and mat a) in the same cell and is thereby self-fertile. We used pyrosequencing of mat-linked SNPs of three heterokaryons to demonstrate that the nuclear ratio is consistently biased for mat A-nuclei during mycelial growth (mean mat A/mat a ratio 87%), but evens out during sexual development (ratio ranging from 40 to 57%). Furthermore, we investigated the association between nuclear ratio and expression of alleles of mat-linked genes and found that expression is coregulated to obtain a tissue-specific bias in expression ratio: during mycelial extension, we found a strong bias in expression for mat A-linked genes, that was independent of nuclear ratio, whereas at the sexual stage we found an expression bias for genes of the mat a nuclei. Taken together, our data indicate that nuclei cooperate to optimize the fitness of the heterokaryon, via both altering their nuclear ratios and coregulation genes expressed in the different nuclei.
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Affiliation(s)
- Nicklas Samils
- Uppsala BioCenter, Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, Uppsala, Sweden
| | - Jonàs Oliva
- Uppsala BioCenter, Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, Uppsala, Sweden
| | - Hanna Johannesson
- Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden
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Corcoran P, Dettman JR, Sun Y, Luque EM, Corrochano LM, Taylor JW, Lascoux M, Johannesson H. A global multilocus analysis of the model fungus Neurospora reveals a single recent origin of a novel genetic system. Mol Phylogenet Evol 2014; 78:136-47. [PMID: 24845789 DOI: 10.1016/j.ympev.2014.05.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2013] [Revised: 02/13/2014] [Accepted: 05/06/2014] [Indexed: 10/25/2022]
Abstract
The large diversity of mating systems observed in the fungal kingdom underlines the importance of mating system change in fungal evolution. The selfing species Neurospora tetrasperma has evolved a novel method of achieving self-fertility by a mating system referred to as pseudohomothallism. However, little is known about the origin of N. tetrasperma and its relationship to the self-sterile, heterothallic, Neurospora species. In this study, we used a combination of phylogenetic and population genetic analyses to reconstruct the evolutionary history of N. tetrasperma and its heterothallic relatives. We sequenced 9 unlinked nuclear loci from 106 strains of N. tetrasperma sampled from across the globe, and a sample of 28 heterothallic strains of Neurospora. Our analyses provide strong support for monophyly of N. tetrasperma, but reject the monophyly of N. crassa. We estimate that N. tetrasperma is of a recent origin and that it diverged from the heterothallic species ∼1 million years ago. We also extend previous findings on the diversification within the N. tetrasperma clade, with 10 lineages identified. Taken together, these findings indicate that N. tetrasperma is younger than has been previously reported and that a rapid diversification of lineages has occurred within the N. tetrasperma clade.
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Affiliation(s)
- Pádraic Corcoran
- Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden.
| | - Jeremy R Dettman
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | - Yu Sun
- Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden
| | - Eva M Luque
- Departamento de Genética, Universidad de Sevilla, Sevilla, Spain
| | | | - John W Taylor
- Department of Plant and Microbial Biology, University of California Berkeley, Berkeley, CA, USA
| | - Martin Lascoux
- Department of Plant Ecology and Evolution, Uppsala University, Uppsala, Sweden
| | - Hanna Johannesson
- Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden
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Maintaining two mating types: structure of the mating type locus and its role in heterokaryosis in Podospora anserina. Genetics 2014; 197:421-32. [PMID: 24558260 DOI: 10.1534/genetics.113.159988] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Pseudo-homothallism is a reproductive strategy elected by some fungi producing heterokaryotic sexual spores containing genetically different but sexually compatible nuclei. This lifestyle appears as a compromise between true homothallism (self-fertility with predominant inbreeding) and complete heterothallism (with exclusive outcrossing). However, pseudohomothallic species face the problem of maintaining heterokaryotic mycelia to fully benefit from this lifestyle, as homokaryons are self-sterile. Here, we report on the structure of chromosome 1 in mat+ and mat- isolates of strain S of the pseudohomothallic fungus Podospora anserina. Chromosome 1 contains either one of the mat+ and mat- mating types of P. anserina, which is mostly found in nature as a mat+/mat- heterokaryotic mycelium harboring sexually compatible nuclei. We identified a "mat" region ∼0.8 Mb long, devoid of meiotic recombination and containing the mating-type idiomorphs, which is a candidate to be involved in the maintenance of the heterokaryotic state, since the S mat+ and S mat- strains have different physiology that may enable hybrid-vigor-like phenomena in the heterokaryons. The mat region contains 229 coding sequences. A total of 687 polymorphisms were detected between the S mat+ and S mat- chromosomes. Importantly, the mat region is colinear between both chromosomes, which calls for an original mechanism of recombination inhibition. Microarray analyses revealed that 10% of the P. anserina genes have different transcriptional profiles in S mat+ and S mat-, in line with their different phenotypes. Finally, we show that the heterokaryotic state is faithfully maintained during mycelium growth of P. anserina, yet mat+/mat+ and mat-/mat- heterokaryons are as stable as mat+/mat- ones, evidencing a maintenance of heterokaryosis that does not rely on fitness-enhancing complementation between the S mat+ and S mat- strains.
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Samils N, Gioti A, Karlsson M, Sun Y, Kasuga T, Bastiaans E, Wang Z, Li N, Townsend JP, Johannesson H. Sex-linked transcriptional divergence in the hermaphrodite fungus Neurospora tetrasperma. Proc Biol Sci 2013; 280:20130862. [PMID: 23782882 PMCID: PMC3712418 DOI: 10.1098/rspb.2013.0862] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
In the filamentous ascomycete Neurospora tetrasperma, a large (approx. 7 Mbp) region of suppressed recombination surrounds the mating-type (mat) locus. While the remainder of the genome is largely homoallelic, this region of recombinational suppression, extending over 1500 genes, is associated with sequence divergence. Here, we used microarrays to examine how the molecular phenotype of gene expression level is linked to this divergent region, and thus to the mating type. Culturing N. tetrasperma on agar media that induce sexual/female or vegetative/male tissue, we found 196 genes significantly differentially expressed between mat A and mat a mating types. Our data show that the genes exhibiting mat-linked expression are enriched in the region genetically linked to mating type, and sequence and expression divergence are positively correlated. Our results indicate that the phenotype of mat A strains is optimized for traits promoting sexual/female development and the phenotype of mat a strains for vegetative/male development. This discovery of differentially expressed genes associated with mating type provides a link between genotypic and phenotypic divergence in this taxon and illustrates a fungal analogue to sexual dimorphism found among animals and plants.
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Affiliation(s)
- Nicklas Samils
- Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences, PO Box 7026, 75007 Uppsala, Sweden
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