The Plot Thickens: Haploid and Triploid-Like Thalli, Hybridization, and Biased Mating Type Ratios in Letharia

AbstractThe study of the reproductive biology of lichen fungal symbionts has been traditionally challenging due to their complex and symbiotic lifestyles. Against the common belief of haploidy, a recent genomic study found a triploid-like signal in Letharia. Here, we used genomic data from a pure culture and from thalli, together with a PCR survey of the MAT locus, to infer the genome organization and reproduction in Letharia. We found that the read count variation in the four Letharia specimens, including the pure culture derived from a single sexual spore of L. lupina, is consistent with haploidy. By contrast, the L. lupina read counts from a thallus’ metagenome are triploid-like. Characterization of the mating-type locus revealed a conserved heterothallic configuration across the genus, along with auxiliary genes that we identified. We found that the mating-type distributions are balanced in North America for L. vulpina and L. lupina, suggesting widespread sexual reproduction, but highly skewed in Europe for L. vulpina, consistent with predominant asexuality. Taken together, we propose that Letharia fungi are heterothallic and typically haploid, and provide evidence that triploid-like individuals are rare hybrids between L. lupina and an unknown Letharia lineage, reconciling classic systematic and genetic studies with recent genomic observations.

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Mating Type in Chlamydomonas Is Specified by mid, the Minus-Dominance Gene

Genetics ◽

10.1093/genetics/146.3.859 ◽

1997 ◽

Vol 146 (3) ◽

pp. 859-869 ◽

Cited By ~ 2

Author(s):

Patrick J Ferris ◽

Ursula W Goodenough

Keyword(s):

Transcription Factor ◽

Mating Type ◽

Codon Bias ◽

Leucine Zipper ◽

Laboratory Strain ◽

Leucine Zipper Motif ◽

Type Locus ◽

Diploid Cells ◽

Necessary And Sufficient

Diploid cells of Chlamydomonas reinhardtii that are heterozygous at the mating-type locus (mt +/mt –) differentiate as minus gametes, a phenomenon known as minus dominance. We report the cloning and characterization of a gene that is necessary and sufficient to exert this minus dominance over the plus differentiation program. The gene, called mid, is located in the rearranged (R) domain of the mt – locus, and has duplicated and transposed to an autosome in a laboratory strain. The imp11 mt – mutant, which differentiates as a fusion-incompetent plus gamete, carries a point mutation in mid. Like the fus1 gene in the mt + locus, mid displays low codon bias compared with other nuclear genes. The mid sequence carries a putative leucine zipper motif, suggesting that it functions as a transcription factor to switch on the minus program and switch off the plus program of gametic differentiation. This is the first sex-determination gene to be characterized in a green organism.

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Homothallic mating type switching generates lethal chromosome breaks in rad52 strains of Saccharomyces cerevisiae

Molecular and Cellular Biology ◽

10.1128/mcb.1.6.522-534.1981 ◽

1981 ◽

Vol 1 (6) ◽

pp. 522-534

Author(s):

B Weiffenbach ◽

J E Haber

Keyword(s):

Saccharomyces Cerevisiae ◽

Mating Type ◽

Deoxyribonucleic Acid ◽

Type Locus ◽

Mating Type Switching ◽

Lethal Event ◽

Bona Fide ◽

Chromosome Iii ◽

Mat Locus ◽

Type Information

In homothallic cells of Saccharomyces cerevisiae, a or alpha mating type information at the mating type locus (MAT) is replaced by the transposition of the opposite mating type allele from HML alpha or HMRa. The rad52-1 mutation, which reduces mitotic and abolishes meiotic recombination, also affects homothallic switching (Malone and Esposito, Proc. Natl. Acad. Sci. U.S.A. 77:503-507, 1980). We have found that both HO rad52 MATa and HO rad52 MAT alpha cells die. This lethality is suppressed by mutations that substantially reduce but do not eliminate homothallic conversions. These mutations map at or near the MAT locus (MAT alpha inc, MATa-inc, MATa stk1) or are unlinked to MAT (HO-1 and swi1). These results suggest that the switching event itself is involved in the lethality. With the exception of swi1, HO rad52 strains carrying one of the above mutations cannot convert mating type at all. MAT alpha rad52 HO swi1 strains apparently can switch MAT alpha to MATa. However, when we analyzed these a maters, we found that few, if any, of them were bona fide MATa cells. These a-like cells were instead either deleted for part of chromosome III distal to and including MAT or had lost the entire third chromosome. Approximately 30% of the time, an a-like cell could be repaired to a normal MATa genotype if the cell was mated to a RAD52 MAT alpha-inc strain. The effects of rad52 were also studied in mata/MAT alpha-inc rad52/rad52 ho/HO diploids. When this diploid attempted to switch mata to MATa, an unstable broken chromosome was generated in nearly every cell. These studies suggest that homothallic switching involves the formation of a double-stranded deoxyribonucleic acid break or a structure which is labile in rad52 cells and results in a broken chromosome. We propose that the production of a double-stranded deoxyribonucleic acid break is the lethal event in rad52 HO cells.

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Mating type control in Saccharomyces cerevisiae: a frameshift mutation at the common DNA sequence, X, of the HML alpha locus

Molecular and Cellular Biology ◽

10.1128/mcb.4.1.203-211.1984 ◽

1984 ◽

Vol 4 (1) ◽

pp. 203-211

Author(s):

K Tanaka ◽

T Oshima ◽

H Araki ◽

S Harashima ◽

Y Oshima

Keyword(s):

Mating Type ◽

Base Pair ◽

Reading Frame ◽

Base Pair Deletion ◽

A Cell ◽

Alpha Gene ◽

The Common ◽

Type Switch ◽

Diploid Cells ◽

Mat Locus

A mutation defective in the homothallic switching of mating type alleles, designated hml alpha-2, has previously been characterized. The mutation occurred in a cell having the HO MATa HML alpha HMRa genotype, and the mutant culture consisted of ca. 10% a mating type cells, 90% nonmater cells of haploid cell size, and 0.1% sporogenous diploid cells. Genetic analyses revealed that nonmater haploid cells have a defect in the alpha 2 cistron at the MAT locus. This defect was probably caused by transposition of a cassette originating from the hml alpha-2 allele by the process of the homothallic mating type switch. That the MAT locus of the nonmater cells is occupied by a DNA fragment indistinguishable from the Y alpha sequence in electrophoretic mobility was demonstrated by Southern hybridization of the EcoRI-HindIII fragment encoding the MAT locus with a cloned HML alpha gene as the probe. The hml alpha-2 mutation was revealed to be a one-base-pair deletion at the ninth base pair in the X region from the X and Y boundary of the HML locus. This mutation gave rise to a shift in the open reading frame of the alpha 2 cistron. A molecular mechanism for the mating type switch associated with the occurrence of sporogenous diploid cells in the mutant culture is discussed.

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Pervasive Phenotypic Impact of a Large Nonrecombining Introgressed Region in Yeast

Molecular Biology and Evolution ◽

10.1093/molbev/msaa101 ◽

2020 ◽

Vol 37 (9) ◽

pp. 2520-2530 ◽

Cited By ~ 3

Author(s):

Christian Brion ◽

Claudia Caradec ◽

David Pflieger ◽

Anne Friedrich ◽

Joseph Schacherer

Keyword(s):

Mating Type ◽

Budding Yeast ◽

Natural Populations ◽

Phenotypic Effect ◽

Genetic Characteristics ◽

Type Locus ◽

First Time ◽

The Relationship ◽

Insight Into ◽

Introgressed Region

Abstract To explore the origin of the diversity observed in natural populations, many studies have investigated the relationship between genotype and phenotype. In yeast species, especially in Saccharomyces cerevisiae, these studies are mainly conducted using recombinant offspring derived from two genetically diverse isolates, allowing to define the phenotypic effect of genetic variants. However, large genomic variants such as interspecies introgressions are usually overlooked even if they are known to modify the genotype–phenotype relationship. To have a better insight into the overall phenotypic impact of introgressions, we took advantage of the presence of a 1-Mb introgressed region, which lacks recombination and contains the mating-type determinant in the Lachancea kluyveri budding yeast. By performing linkage mapping analyses in this species, we identified a total of 89 loci affecting growth fitness in a large number of conditions and 2,187 loci affecting gene expression mostly grouped into two major hotspots, one being the introgressed region carrying the mating-type locus. Because of the absence of recombination, our results highlight the presence of a sexual dimorphism in a budding yeast for the first time. Overall, by describing the phenotype–genotype relationship in the Lachancea kluyveri species, we expanded our knowledge on how genetic characteristics of large introgression events can affect the phenotypic landscape.

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Homothallic mating type switching generates lethal chromosome breaks in rad52 strains of Saccharomyces cerevisiae.

Molecular and Cellular Biology ◽

10.1128/mcb.1.6.522 ◽

1981 ◽

Vol 1 (6) ◽

pp. 522-534 ◽

Cited By ~ 55

Author(s):

B Weiffenbach ◽

J E Haber

Keyword(s):

Saccharomyces Cerevisiae ◽

Mating Type ◽

Deoxyribonucleic Acid ◽

Type Locus ◽

Mating Type Switching ◽

Lethal Event ◽

Bona Fide ◽

Chromosome Iii ◽

Mat Locus ◽

Type Information

In homothallic cells of Saccharomyces cerevisiae, a or alpha mating type information at the mating type locus (MAT) is replaced by the transposition of the opposite mating type allele from HML alpha or HMRa. The rad52-1 mutation, which reduces mitotic and abolishes meiotic recombination, also affects homothallic switching (Malone and Esposito, Proc. Natl. Acad. Sci. U.S.A. 77:503-507, 1980). We have found that both HO rad52 MATa and HO rad52 MAT alpha cells die. This lethality is suppressed by mutations that substantially reduce but do not eliminate homothallic conversions. These mutations map at or near the MAT locus (MAT alpha inc, MATa-inc, MATa stk1) or are unlinked to MAT (HO-1 and swi1). These results suggest that the switching event itself is involved in the lethality. With the exception of swi1, HO rad52 strains carrying one of the above mutations cannot convert mating type at all. MAT alpha rad52 HO swi1 strains apparently can switch MAT alpha to MATa. However, when we analyzed these a maters, we found that few, if any, of them were bona fide MATa cells. These a-like cells were instead either deleted for part of chromosome III distal to and including MAT or had lost the entire third chromosome. Approximately 30% of the time, an a-like cell could be repaired to a normal MATa genotype if the cell was mated to a RAD52 MAT alpha-inc strain. The effects of rad52 were also studied in mata/MAT alpha-inc rad52/rad52 ho/HO diploids. When this diploid attempted to switch mata to MATa, an unstable broken chromosome was generated in nearly every cell. These studies suggest that homothallic switching involves the formation of a double-stranded deoxyribonucleic acid break or a structure which is labile in rad52 cells and results in a broken chromosome. We propose that the production of a double-stranded deoxyribonucleic acid break is the lethal event in rad52 HO cells.

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When Does Diversity of Agent Preferences Improve Outcomes in Selfish Routing?

Proceedings of the Twenty-Seventh International Joint Conference on Artificial Intelligence ◽

10.24963/ijcai.2018/24 ◽

2018 ◽

Cited By ~ 1

Author(s):

Richard Cole ◽

Thanasis Lianeas ◽

Evdokia Nikolova

Keyword(s):

Common Belief ◽

Selfish Routing ◽

Trade Off ◽

Full Characterization ◽

Improved Outcomes ◽

Network Topologies ◽

Multi Agent ◽

The Common ◽

Routing Games

We seek to understand when heterogeneity in agent preferences yields improved outcomes in terms of overall cost. That this might be hoped for is based on the common belief that diversity is advantageous in many multi-agent settings. We investigate this in the context of routing. Our main result is a sharp characterization of the network settings in which diversity always helps, versus those in which it is sometimes harmful. Specifically, we consider routing games, where diversity arises in the way that agents trade-off two criteria (such as time and money, or, in the case of stochastic delays, expectation and variance of delay). Our main contributions are: 1) A participant-oriented measure of cost in the presence of agent diversity; 2) A full characterization of those network topologies for which diversity always helps, for all latency functions and demands.

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Pervasive phenotypic impact of a large non-recombining introgressed region in yeast

10.1101/2020.01.29.925289 ◽

2020 ◽

Author(s):

Christian Brion ◽

Claudia Caradec ◽

David Pflieger ◽

Anne Friedrich ◽

Joseph Schacherer

Keyword(s):

Mating Type ◽

Budding Yeast ◽

Natural Populations ◽

Phenotypic Effect ◽

Genetic Characteristics ◽

Type Locus ◽

First Time ◽

The Relationship ◽

Insight Into ◽

Introgressed Region

AbstractTo explore the origin of the diversity observed in natural populations, many studies have investigated the relationship between genotype and phenotype. In yeast species, especially in Saccharomyces cerevisiae, these studies are mainly conducted using recombinant offspring derived from two genetically diverse isolates, allowing to define the phenotypic effect of genetic variants. However, large genomic variants such as interspecies introgressions are usually overlooked even if they are known to modify the genotype-phenotype relationship. To have a better insight into the overall phenotypic impact of introgressions, we took advantage of the presence of a 1-Mb introgressed region, which lacks recombination and contains the mating-type determinant in the Lachancea kluyveri budding yeast. By performing linkage mapping analyses in this species, we identified a total of 89 loci affecting growth fitness in a large number of conditions and 2,187 loci affecting gene expression mostly grouped into two major hotspots, one being the introgressed region carrying the mating-type locus. Because of the absence of recombination, our results highlight the presence of a sexual dimorphism in a budding yeast for the first time. Overall, by describing the phenotype-genotype relationship in the L. kluyveri species, we expanded our knowledge on how genetic characteristics of large introgression events can affect the phenotypic landscape.

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