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Effect of Salt Stress on Mutation and Genetic Architecture for Fitness Components in Saccharomyces cerevisiae. G3-GENES GENOMES GENETICS 2020; 10:3831-3842. [PMID: 32847816 PMCID: PMC7534429 DOI: 10.1534/g3.120.401593] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Mutations shape genetic architecture and thus influence the evolvability, adaptation and diversification of populations. Mutations may have different and even opposite effects on separate fitness components, and their rate of origin, distribution of effects and variance-covariance structure may depend on environmental quality. We performed an approximately 1,500-generation mutation-accumulation (MA) study in diploids of the yeast Saccharomyces cerevisiae in stressful (high-salt) and normal environments (50 lines each) to investigate the rate of input of mutational variation (Vm) as well as the mutation rate and distribution of effects on diploid and haploid fitness components, assayed in the normal environment. All four fitness components in both MA treatments exhibited statistically significant mutational variance and mutational heritability. Compared to normal-MA, salt stress increased the mutational variance in growth rate by more than sevenfold in haploids derived from the MA lines. This increase was not detected in diploid growth rate, suggesting masking of mutations in the heterozygous state. The genetic architecture arising from mutation (M-matrix) differed between normal and salt conditions. Salt stress also increased environmental variance in three fitness components, consistent with a reduction in canalization. Maximum-likelihood analysis indicated that stress increased the genomic mutation rate by approximately twofold for maximal growth rate and sporulation rate in diploids and for viability in haploids, and by tenfold for maximal growth rate in haploids, but large confidence intervals precluded distinguishing these values between MA environments. We discuss correlations between fitness components in diploids and haploids and compare the correlations between the two MA environmental treatments.
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Charron G, Marsit S, Hénault M, Martin H, Landry CR. Spontaneous whole-genome duplication restores fertility in interspecific hybrids. Nat Commun 2019; 10:4126. [PMID: 31511504 PMCID: PMC6739354 DOI: 10.1038/s41467-019-12041-8] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2019] [Accepted: 08/19/2019] [Indexed: 11/21/2022] Open
Abstract
Interspecies hybrids often show some advantages over parents but also frequently suffer from reduced fertility, which can sometimes be overcome through sexual reproduction that sorts out genetic incompatibilities. Sex is however inefficient due to the low viability or fertility of hybrid offspring and thus limits their evolutionary potential. Mitotic cell division could be an alternative to fertility recovery in species such as fungi that can also propagate asexually. Here, to test this, we evolve in parallel and under relaxed selection more than 600 diploid yeast inter-specific hybrids that span from 100,000 to 15 M years of divergence. We find that hybrids can recover fertility spontaneously and rapidly through whole-genome duplication. These events occur in both hybrids between young and well-established species. Our results show that the instability of ploidy in hybrid is an accessible path to spontaneous fertility recovery. Hybridization across species can lead to offspring with reduced fertility. Here, the authors experimentally evolve yeast and show that whole-genome duplication during asexual reproduction can restore fertility in hybrids over a relatively short evolutionary timespan.
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Affiliation(s)
- Guillaume Charron
- Institut de Biologie Intégrative et des Systèmes, 1030 avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada.,Regroupement Québécois de Recherche sur la Fonction, l'Ingénierie et les Applications des Protéines, (PROTEO), 1045 Avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada.,Département de biologie, 1045 Avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada
| | - Souhir Marsit
- Institut de Biologie Intégrative et des Systèmes, 1030 avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada.,Regroupement Québécois de Recherche sur la Fonction, l'Ingénierie et les Applications des Protéines, (PROTEO), 1045 Avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada.,Département de biologie, 1045 Avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada.,Département de biochimie, microbiologie et bio-informatique, 1045 Avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada
| | - Mathieu Hénault
- Institut de Biologie Intégrative et des Systèmes, 1030 avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada.,Regroupement Québécois de Recherche sur la Fonction, l'Ingénierie et les Applications des Protéines, (PROTEO), 1045 Avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada.,Département de biochimie, microbiologie et bio-informatique, 1045 Avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada
| | - Hélène Martin
- Institut de Biologie Intégrative et des Systèmes, 1030 avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada.,Regroupement Québécois de Recherche sur la Fonction, l'Ingénierie et les Applications des Protéines, (PROTEO), 1045 Avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada.,Département de biologie, 1045 Avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada.,Département de biochimie, microbiologie et bio-informatique, 1045 Avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada
| | - Christian R Landry
- Institut de Biologie Intégrative et des Systèmes, 1030 avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada. .,Regroupement Québécois de Recherche sur la Fonction, l'Ingénierie et les Applications des Protéines, (PROTEO), 1045 Avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada. .,Département de biologie, 1045 Avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada. .,Département de biochimie, microbiologie et bio-informatique, 1045 Avenue de la Médecine, Université Laval, Québec (Qc), G1V 0A6, Canada.
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Integrated transcriptomic and proteomic analysis of the ethanol stress response in Saccharomyces cerevisiae Sc131. J Proteomics 2019; 203:103377. [DOI: 10.1016/j.jprot.2019.103377] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2018] [Revised: 04/12/2019] [Accepted: 05/12/2019] [Indexed: 12/29/2022]
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Ostrowski EA, Ofria C, Lenski RE. Genetically integrated traits and rugged adaptive landscapes in digital organisms. BMC Evol Biol 2015; 15:83. [PMID: 25963618 PMCID: PMC4428022 DOI: 10.1186/s12862-015-0361-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2014] [Accepted: 04/24/2015] [Indexed: 05/28/2023] Open
Abstract
BACKGROUND When overlapping sets of genes encode multiple traits, those traits may not be able to evolve independently, resulting in constraints on adaptation. We examined the evolution of genetically integrated traits in digital organisms-self-replicating computer programs that mutate, compete, adapt, and evolve in a virtual world. We assessed whether overlap in the encoding of two traits - here, the ability to perform different logic functions - constrained adaptation. We also examined whether strong opposing selection could separate otherwise entangled traits, allowing them to be independently optimized. RESULTS Correlated responses were often asymmetric. That is, selection to increase one function produced a correlated response in the other function, while selection to increase the second function caused a complete loss of the ability to perform the first function. Nevertheless, most pairs of genetically integrated traits could be successfully disentangled when opposing selection was applied to break them apart. In an interesting exception to this pattern, the logic function AND evolved counter to its optimum in some populations owing to selection on the EQU function. Moreover, the EQU function showed the strongest response to selection only after it was disentangled from AND, such that the ability to perform AND was lost. Subsequent analyses indicated that selection against AND had altered the local adaptive landscape such that populations could cross what would otherwise have been an adaptive valley and thereby reach a higher fitness peak. CONCLUSIONS Correlated responses to selection can sometimes constrain adaptation. However, in our study, even strongly overlapping genes were usually insufficient to impose long-lasting constraints, given the input of new mutations that fueled selective responses. We also showed that detailed information about the adaptive landscape was useful for predicting the outcome of selection on correlated traits. Finally, our results illustrate the richness of evolutionary dynamics in digital systems and highlight their utility for studying processes thought to be important in biological systems, but which are difficult to investigate in those systems.
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Affiliation(s)
- Elizabeth A Ostrowski
- Department of Biology and Biochemistry, University of Houston, Houston, TX, 77204, USA.
| | - Charles Ofria
- Department of Computer Science and Engineering, Michigan State University, East Lansing, MI, 48824, USA. .,BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, MI, 48824, USA.
| | - Richard E Lenski
- BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, MI, 48824, USA. .,Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI, 48824, USA.
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Li D, Yan Z, Lu L, Jiang H, Wang W. Pleiotropy of the de novo-originated gene MDF1. Sci Rep 2014; 4:7280. [PMID: 25452167 PMCID: PMC4250933 DOI: 10.1038/srep07280] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2014] [Accepted: 11/11/2014] [Indexed: 12/20/2022] Open
Abstract
MDF1 is a young de novo-originated gene from a non-coding sequence in baker's yeast, S. cerevisiae, which can suppress mating and promote vegetative growth. Our previous experiments successfully demonstrated how Mdf1p binds to the key mating pathway determinant MATα2 to suppress mating. However, how Mdf1p promotes growth and fulfills the crosstalk between the yeast mating and growth pathways are still open questions. Thus, the adaptive significance of this new de novo gene remains speculative. Here, we show that Mdf1p shortens the lag phase of S. cerevisiae by physically interacting with SNF1, the governing factor for nonfermentable carbon source utilization, and thereby confers a selective advantage on yeasts through the rapid consumption of glucose in the early generational stage in rich medium. Therefore, MDF1 functions in two important molecular pathways, mating and fermentation, and mediates the crosstalk between reproduction and vegetative growth. Together, our results provide a comprehensive example of how a de novo-originated gene organizes new regulatory circuits and thereby confers a selective advantage on S. cerevisiae to allow exquisite adaptation to the changing environment.
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Affiliation(s)
- Dan Li
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences (CAS), Kunming, Yunnan 650223, People's Republic of China
| | - Zhihui Yan
- Key Laboratory of Systems Microbial Biotechnology, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences(CAS), Tianjin 300308, People's Republic of China
| | - Lina Lu
- Key Laboratory of Systems Microbial Biotechnology, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences(CAS), Tianjin 300308, People's Republic of China
| | - Huifeng Jiang
- Key Laboratory of Systems Microbial Biotechnology, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences(CAS), Tianjin 300308, People's Republic of China
| | - Wen Wang
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences (CAS), Kunming, Yunnan 650223, People's Republic of China
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Zarin T, Moses AM. Insights into molecular evolution from yeast genomics. Yeast 2014; 31:233-41. [PMID: 24760744 DOI: 10.1002/yea.3018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2014] [Revised: 04/09/2014] [Accepted: 04/10/2014] [Indexed: 12/13/2022] Open
Abstract
Enabled by comparative genomics, yeasts have increasingly developed into a powerful model system for molecular evolution. Here we survey several areas in which yeast studies have made important contributions, including regulatory evolution, gene duplication and divergence, evolution of gene order and evolution of complexity. In each area we highlight key studies and findings based on techniques ranging from statistical analysis of large datasets to direct laboratory measurements of fitness. Future work will combine traditional evolutionary genetics analysis and experimental evolution with tools from systems biology to yield mechanistic insight into complex phenotypes.
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Affiliation(s)
- Taraneh Zarin
- Department of Cell and Systems Biology, University of Toronto, ON, Canada
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Freschi L, Torres-Quiroz F, Dubé AK, Landry CR. qPCA: a scalable assay to measure the perturbation of protein-protein interactions in living cells. MOLECULAR BIOSYSTEMS 2012; 9:36-43. [PMID: 23099892 DOI: 10.1039/c2mb25265a] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
One of the most important challenges in systems biology is to understand how cells respond to genetic and environmental perturbations. Here we show that the yeast DHFR-PCA, coupled with high-resolution growth profiling (DHFR-qPCA), is a straightforward assay to study the modulation of protein-protein interactions (PPIs) in vivo as a response to genetic, metabolic and drug perturbations. Using the canonical Protein Kinase A (PKA) pathway as a test system, we show that changes in PKA activity can be measured in living cells as a modulation of the interaction between its regulatory (Bcy1) and catalytic (Tpk1 and Tpk2) subunits in response to changes in carbon metabolism, caffeine and methyl methanesulfonate (MMS) treatments and to modifications in the dosage of its enzymatic regulators, the phosphodiesterases. Our results show that the DHFR-qPCA is easily implementable and amenable to high-throughput. The DHFR-qPCA will pave the way to the study of the effects of drug, genetic and environmental perturbations on in vivo PPI networks, thus allowing the exploration of new spaces of the eukaryotic interactome.
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Affiliation(s)
- Luca Freschi
- Institut de Biologie Intégrative et des Systèmes (IBIS), Université Laval, Québec, Canada
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Asexual reproduction induces a rapid and permanent loss of sexual reproduction capacity in the rice fungal pathogen Magnaporthe oryzae: results of in vitro experimental evolution assays. BMC Evol Biol 2012; 12:42. [PMID: 22458778 PMCID: PMC3379926 DOI: 10.1186/1471-2148-12-42] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2011] [Accepted: 03/29/2012] [Indexed: 12/15/2022] Open
Abstract
Background Sexual reproduction is common in eukaryotic microorganisms, with few species reproducing exclusively asexually. However, in some organisms, such as fungi, asexual reproduction alternates with episodic sexual reproduction events. Fungi are thus appropriate organisms for studies of the reasons for the selection of sexuality or clonality and of the mechanisms underlying this selection. Magnaporthe oryzae, an Ascomycete causing blast disease on rice, reproduces mostly asexually in natura. Sexual reproduction is possible in vitro and requires (i) two strains of opposite mating types including (ii) at least one female-fertile strain (i.e. a strain able to produce perithecia, the female organs in which meiosis occurs). Female-fertile strains are found only in limited areas of Asia, in which evidence for contemporary recombination has recently been obtained. We induced the forced evolution of four Chinese female-fertile strains in vitro by the weekly transfer of asexual spores (conidia) between Petri dishes. We aimed to determine whether female fertility was rapidly lost in the absence of sexual reproduction and whether this loss was controlled genetically or epigenetically. Results All the strains became female-sterile after 10 to 19 rounds of selection under asexual conditions. As no single-spore isolation was carried out, the observed decrease in the production of perithecia reflected the emergence and the invasion of female-sterile mutants. The female-sterile phenotype segregated in the offspring of crosses between female-sterile evolved strains and female-fertile wild-type strains. This segregation was maintained in the second generation in backcrosses. Female-sterile evolved strains were subjected to several stresses, but none induced the restoration of female fertility. This loss of fertility was therefore probably due to genetic rather than epigenetic mechanisms. In competition experiments, female-sterile mutants produced similar numbers of viable conidia to wild-type strains, but released them more efficiently. This advantage may account for the invasion of our populations by female-sterile mutants. Conclusions We show for the first time that, in the absence of sexual reproduction, female-sterile mutants of M. oryzae rice strains can arise and increase in abundance in asexual generations. This change in phenotype was frequent and probably caused by mutation. These results suggest that female fertility may have been lost rapidly during the dispersion of the fungus from Asia to the rest of the world.
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Raynes Y, Gazzara MR, Sniegowski PD. Mutator dynamics in sexual and asexual experimental populations of yeast. BMC Evol Biol 2011; 11:158. [PMID: 21649918 PMCID: PMC3141426 DOI: 10.1186/1471-2148-11-158] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2011] [Accepted: 06/07/2011] [Indexed: 12/05/2022] Open
Abstract
Background In asexual populations, mutators may be expected to hitchhike with associated beneficial mutations. In sexual populations, recombination is predicted to erode such associations, inhibiting mutator hitchhiking. To investigate the effect of recombination on mutators experimentally, we compared the frequency dynamics of a mutator allele (msh2Δ) in sexual and asexual populations of Saccharomyces cerevisiae. Results Mutator strains increased in frequency at the expense of wild-type strains in all asexual diploid populations, with some approaching fixation in 150 generations of propagation. Over the same period of time, mutators declined toward loss in all corresponding sexual diploid populations as well as in haploid populations propagated asexually. Conclusions We report the first experimental investigation of mutator dynamics in sexual populations. We show that a strong mutator quickly declines in sexual populations while hitchhiking to high frequency in asexual diploid populations, as predicted by theory. We also show that the msh2Δ mutator has a high and immediate realized cost that is alone sufficient to explain its decline in sexual populations. We postulate that this cost is indirect; namely, that it is due to a very high rate of recessive lethal or strongly deleterious mutation. However, we cannot rule out the possibility that msh2Δ also has unknown directly deleterious effects on fitness, and that these effects may differ between haploid asexual and sexual populations. Despite these reservations, our results prompt us to speculate that the short-term cost of highly deleterious recessive mutations can be as important as recombination in preventing mutator hitchhiking in sexual populations.
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Affiliation(s)
- Yevgeniy Raynes
- Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018, USA.
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11
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Abstract
Pleiotropy refers to the phenomenon of a single mutation or gene affecting multiple distinct phenotypic traits and has broad implications in many areas of biology. Due to its central importance, pleiotropy has also been extensively modeled, albeit with virtually no empirical basis. Analyzing phenotypes of large numbers of yeast, nematode, and mouse mutants, we here describe the genomic patterns of pleiotropy. We show that the fraction of traits altered appreciably by the deletion of a gene is minute for most genes and the gene-trait relationship is highly modular. The standardized size of the phenotypic effect of a gene on a trait is approximately normally distributed with variable SDs for different genes, which gives rise to the surprising observation of a larger per-trait effect for genes affecting more traits. This scaling property counteracts the pleiotropy-associated reduction in adaptation rate (i.e., the "cost of complexity") in a nonlinear fashion, resulting in the highest adaptation rate for organisms of intermediate complexity rather than low complexity. Intriguingly, the observed scaling exponent falls in a narrow range that maximizes the optimal complexity. Together, the genome-wide observations of overall low pleiotropy, high modularity, and larger per-trait effects from genes of higher pleiotropy necessitate major revisions of theoretical models of pleiotropy and suggest that pleiotropy has not only allowed but also promoted the evolution of complexity.
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12
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Cavalier-Smith T. Origin of the cell nucleus, mitosis and sex: roles of intracellular coevolution. Biol Direct 2010; 5:7. [PMID: 20132544 PMCID: PMC2837639 DOI: 10.1186/1745-6150-5-7] [Citation(s) in RCA: 139] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2009] [Accepted: 02/04/2010] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND The transition from prokaryotes to eukaryotes was the most radical change in cell organisation since life began, with the largest ever burst of gene duplication and novelty. According to the coevolutionary theory of eukaryote origins, the fundamental innovations were the concerted origins of the endomembrane system and cytoskeleton, subsequently recruited to form the cell nucleus and coevolving mitotic apparatus, with numerous genetic eukaryotic novelties inevitable consequences of this compartmentation and novel DNA segregation mechanism. Physical and mutational mechanisms of origin of the nucleus are seldom considered beyond the long-standing assumption that it involved wrapping pre-existing endomembranes around chromatin. Discussions on the origin of sex typically overlook its association with protozoan entry into dormant walled cysts and the likely simultaneous coevolutionary, not sequential, origin of mitosis and meiosis. RESULTS I elucidate nuclear and mitotic coevolution, explaining the origins of dicer and small centromeric RNAs for positionally controlling centromeric heterochromatin, and how 27 major features of the cell nucleus evolved in four logical stages, making both mechanisms and selective advantages explicit: two initial stages (origin of 30 nm chromatin fibres, enabling DNA compaction; and firmer attachment of endomembranes to heterochromatin) protected DNA and nascent RNA from shearing by novel molecular motors mediating vesicle transport, division, and cytoplasmic motility. Then octagonal nuclear pore complexes (NPCs) arguably evolved from COPII coated vesicle proteins trapped in clumps by Ran GTPase-mediated cisternal fusion that generated the fenestrated nuclear envelope, preventing lethal complete cisternal fusion, and allowing passive protein and RNA exchange. Finally, plugging NPC lumens by an FG-nucleoporin meshwork and adopting karyopherins for nucleocytoplasmic exchange conferred compartmentation advantages. These successive changes took place in naked growing cells, probably as indirect consequences of the origin of phagotrophy. The first eukaryote had 1-2 cilia and also walled resting cysts; I outline how encystation may have promoted the origin of meiotic sex. I also explain why many alternative ideas are inadequate. CONCLUSION Nuclear pore complexes are evolutionary chimaeras of endomembrane- and mitosis-related chromatin-associated proteins. The keys to understanding eukaryogenesis are a proper phylogenetic context and understanding organelle coevolution: how innovations in one cell component caused repercussions on others.
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Affiliation(s)
- Sarah P Otto
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada.
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van der Nest MA, Slippers B, Steenkamp ET, De Vos L, Van Zyl K, Stenlid J, Wingfield MJ, Wingfield BD. Genetic linkage map for Amylostereum areolatum reveals an association between vegetative growth and sexual and self-recognition. Fungal Genet Biol 2009; 46:632-41. [PMID: 19523529 DOI: 10.1016/j.fgb.2009.06.002] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2008] [Revised: 06/01/2009] [Accepted: 06/02/2009] [Indexed: 10/20/2022]
Abstract
Amylostereum areolatum is a filamentous fungus that grows through tip extension, branching and hyphal fusion. In the homokaryotic phase, the hyphae of different individuals are capable of fusing followed by heterokaryon formation, only if they have dissimilar allelic specificities at their mating-type (mat) loci. In turn, hyphal fusion between heterokaryons persists only when they share the same alleles at all of their heterokaryon incompatibility (het) loci. In this study we present the first genetic linkage map for A. areolatum, onto which the mat and het loci, as well as quantitative trait loci (QTLs) for mycelial growth rate are mapped. The recognition loci (mat-A and het-A) are positioned near QTLs associated with mycelial growth, suggesting that the genetic determinants influencing recognition and growth rate in A. areolatum are closely associated. This was confirmed when isolates associated with specific mat and het loci displayed significantly different mycelial growth rates. Although the link between growth and sexual recognition has previously been observed in other fungi, this is the first time that an association between growth and self-recognition has been shown.
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Affiliation(s)
- M A van der Nest
- Department of Genetics, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, South Africa.
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15
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Keller PJ, Knop M. Evolution of mutational robustness in the yeast genome: a link to essential genes and meiotic recombination hotspots. PLoS Genet 2009; 5:e1000533. [PMID: 19557188 PMCID: PMC2694357 DOI: 10.1371/journal.pgen.1000533] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2008] [Accepted: 05/22/2009] [Indexed: 01/21/2023] Open
Abstract
Deleterious mutations inevitably emerge in any evolutionary process and are speculated to decisively influence the structure of the genome. Meiosis, which is thought to play a major role in handling mutations on the population level, recombines chromosomes via non-randomly distributed hot spots for meiotic recombination. In many genomes, various types of genetic elements are distributed in patterns that are currently not well understood. In particular, important (essential) genes are arranged in clusters, which often cannot be explained by a functional relationship of the involved genes. Here we show by computer simulation that essential gene (EG) clustering provides a fitness benefit in handling deleterious mutations in sexual populations with variable levels of inbreeding and outbreeding. We find that recessive lethal mutations enforce a selective pressure towards clustered genome architectures. Our simulations correctly predict (i) the evolution of non-random distributions of meiotic crossovers, (ii) the genome-wide anti-correlation of meiotic crossovers and EG clustering, (iii) the evolution of EG enrichment in pericentromeric regions and (iv) the associated absence of meiotic crossovers (cold centromeres). Our results furthermore predict optimal crossover rates for yeast chromosomes, which match the experimentally determined rates. Using a Saccharomyces cerevisiae conditional mutator strain, we show that haploid lethal phenotypes result predominantly from mutation of single loci and generally do not impair mating, which leads to an accumulation of mutational load following meiosis and mating. We hypothesize that purging of deleterious mutations in essential genes constitutes an important factor driving meiotic crossover. Therefore, the increased robustness of populations to deleterious mutations, which arises from clustered genome architectures, may provide a significant selective force shaping crossover distribution. Our analysis reveals a new aspect of the evolution of genome architectures that complements insights about molecular constraints, such as the interference of pericentromeric crossovers with chromosome segregation.
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Affiliation(s)
- Philipp J. Keller
- European Molecular Biology Laboratory (EMBL), Cell Biology and Biophysics Unit, Heidelberg, Germany
| | - Michael Knop
- European Molecular Biology Laboratory (EMBL), Cell Biology and Biophysics Unit, Heidelberg, Germany
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Campos PRA, Wahl LM. The effects of population bottlenecks on clonal interference, and the adaptation effective population size. Evolution 2009; 63:950-8. [PMID: 19210533 DOI: 10.1111/j.1558-5646.2008.00595.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Clonal interference refers to the competition that arises in asexual populations when multiple beneficial mutations segregate simultaneously. A large body of theoretical and experimental work now addresses this issue. Although much of the experimental work is performed in populations that grow exponentially between periodic population bottlenecks, the theoretical work to date has addressed only populations of a constant size. We derive an analytical approximation for the rate of adaptation in the presence of both clonal interference and bottlenecks, and compare this prediction to the results of an individual-based simulation, showing excellent agreement in the parameter regime in which clonal interference prevails. We also derive an appropriate definition for the effective population size for adaptive evolution experiments in the presence of population bottlenecks. This "adaptation effective population size" allows for a good approximation of the expected rate of adaptation, either in the strong-selection weak-mutation regime, or when clonal interference comes into play. In the multiple mutation regime, when the product of the population size and mutation rate is extremely large, these results no longer hold.
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Affiliation(s)
- Paolo R A Campos
- Departamento de Física, Universidade Federal Rural de Pernambuco, Dois Irmãos, 52171-900, Recife-PE, Brazil
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Unravelling the evolutionary advantage of sex: a commentary on ‘Mutation–selection balance and the evolutionary advantage of sex and recombination’ by Brian Charlesworth. Genet Res (Camb) 2008; 89:447-9. [PMID: 18976534 DOI: 10.1017/s001667230800966x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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Current awareness on yeast. Yeast 2007. [DOI: 10.1002/yea.1454] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
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