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Hanna Johannesson - One of the best experts on this subject based on the ideXlab platform.
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Deciphering the Relationship between Mating System and the Molecular Evolution of the Pheromone and Receptor Genes in Neurospora
Molecular biology and evolution, 2012Co-Authors: Kristiina Nygren, Anastasia Gioti, Rebecka Strandberg, Magnus Karlsson, Hanna JohannessonAbstract:Here, we present a study of the molecular evolution of the pheromone receptor genes (pre-1 and pre-2) in Neurospora taxa with different mating systems. We focus on comparisons between heterothallic and homothallic taxa, reproducing sexually by outcrossing and by intrahaploid selfing, respectively. Our general aim was to use a phylogenetic framework to investigate whether the evolutionary trajectory of the pheromone and receptor genes in Neurospora differs between heterothallic and homothallic taxa, and among the homothallic lineages/clades previously indicated to represent independent switches from heterothallism to Homothallism in the evolutionary history of the genus. We complemented molecular evolution analyses with an expression study of the pre genes and their upstream regulators, the mating-type (mat) genes, in homothallic taxa. Our analyses suggest that the pheromone receptor gene pre-1 is functionally conserved in both heterothallic and homothallic taxa. Moreover, we found evidence of positive selection for a small fraction of codons in the cytoplasmic signal-transducing C-terminal region of the protein PRE-1. Distribution of positively selected codons differs between heterothallic and homothallic groups, suggesting functional divergence associated with mating system. The gene pre-2 was shown to evolve under high selective constraints, with no strong evidence for positive selection. Although our data suggest that both pre-1 and pre-2 are overall functional in homothallic taxa, individual taxa display frame-shift mutations causing premature stop codons, which might indicate loss of function. Transcriptional patterns of pre and mat genes in six homothallic taxa, selected to represent six different switches from heterothallism to Homothallism, do not support a universal pattern of regulation of these genes during reproductive tissue development. Taken together, our analyses suggest that the pheromone receptor genes pre-1 and pre-2 are in general functional in homothallic Neurospora taxa, in contrast with the situation for the mat genes that are generally degenerate in these taxa.
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Unidirectional Evolutionary Transitions in Fungal Mating Systems and the Role of Transposable Elements
Molecular biology and evolution, 2012Co-Authors: Anastasia Gioti, Alexandra A. Mushegian, Rebecka Strandberg, Jason E. Stajich, Hanna JohannessonAbstract:The aim of this thesis was to study the evolution of reproductive systems and reproductive traits in the fungal genus Neurospora. More specifically, I have investigated the evolutionary forces shaping the genes involved in sexual reproduction, focusing on mating-type (mat) and pheromone receptor (pre) genes. Neurospora contains species exhibiting three different mating systems, i.e., heterothallism (self-incompatibility), Homothallism (self-compatibility) and pseudoHomothallism (partial self-incompatibility). First, a robust phylogeny of Neurospora was established. The phylogenetic analyses revealed multiple independent transitions in reproductive life style during the evolutionary history of the genus. We argued for a heterothallic ancestor of the genus, although our subsequent ancestral reconstruction analyses favored a homothallic ancestor. To be able to settle the ancestral mating system, we zoomed in on the structural architecture of the mat-locus in four homothallic species of Neurospora, thought to have arisen from independent transitions. Our results led us to suggest two different genetic mechanisms (translocation and unequal crossover) to explain the transitions in mating system from heterothallism to Homothallism. We pointed out that the mating-system transitions in Neurospora are unidirectional, and suggested that transposable elements might be driving the transitions. In conclusion, we suggest a heterothallic ancestor for Neurospora, and that at least six transitions to Homothallism and two transitions to pseudoHomothallism have occurred in its evolutionary history. Further, we used the phylogeny of Neurospora as a framework to test if the evolution of pre-genes (pre-1 and pre-2) in hetero- and homothallic Neurospora is dependent on mating systems and/or even the homothallic clades themselves (i.e., mating-system and/or switch-dependent). The molecular evolution results suggest that pre-1 and pre-2 are overall functional in both homothallic and heterothallic Neurospora. The molecular evolution of pre-1 seems to be independent of mating-system or homothallic clade, and we detected signs for positive selection in the C-terminal tail. For pre-2 we found no support for mating-system dependent evolution, but indications for switch-dependent evolution. In this study we also included expression analyses of both pre- as well as mat-genes, with the prospect to assess functionality and regulation. During this thesis work, we also performed a phylogenetic study were we found that reproductive genes might be more permeable to introgression than other genes, which is in contrast to theoretical expectations. In the last study, we confirmed the co-existence of two alternative splice variants of the pheromone receptor gene pre-1 in Neurospora crassa, and performed expression profiles studies using quantitative RT-PCR. I hope this thesis work will further strengthen Neurospora as a model for research in evolutionary genetics.
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Research article Unidirectional Evolutionary Transitions in Fungal Mating Systems and the Role of Transposable Elements
2012Co-Authors: Anastasia Gioti, Alexandra A. Mushegian, Rebecka Strandberg, Jason E. Stajich, Hanna JohannessonAbstract:In the fungal kingdom, the evolution of mating systems is highly dynamic, varying even among closely related species. Rearrangements in the mating-type (mat) locus, which contains the major regulators of sexual development, are expected to underlie the transitions between self-sterility (heterothallism) and self-fertility (Homothallism). However, both the genetic mechanisms and the direction of evolutionary transitions in fungal mating systems are under debate. Here, we present new sequences of the mat locus of four homothallic and one heterothallic species of the model genus Neurospora (Ascomycota). By examining the patterns of synteny among these sequences and previously published data, we show that the locus is conserved among heterothallic species belonging to distinct phylogenetic clades, while different gene arrangements characterize the four homothallic species. These results allowed us to ascertain a heterothallic ancestor for the genus, confirming the prediction of the dead-end theory on unidirectional transitions toward selfing. We show that at least four shifts from heterothallism to Homothallism have occurred in Neurospora, three of which involve the acquisition of sequences of both mating types into the same haploid genome. We present evidence for two genetic mechanisms allowing these shifts: translocation and unequal crossover. Finally, we identified two novel retrotransposons and suggest that these have played a major role in mating-system transitions, by facilitating multiple rearrangements of the mat locus.
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Research article Deciphering the Relationship between Mating System and the Molecular Evolution of the Pheromone and Receptor Genes in Neurospora
2012Co-Authors: Kristiina Nygren, Anastasia Gioti, Rebecka Strandberg, Magnus Karlsson, Hanna JohannessonAbstract:Here, we present a study of the molecular evolution of the pheromone receptor genes (pre-1 and pre-2 )i nNeurospora taxa with different mating systems. We focus on comparisons between heterothallic and homothallic taxa, reproducing sexually by outcrossing and by intrahaploid selfing, respectively. Our general aim was to use a phylogenetic framework to investigate whether the evolutionary trajectory of the pheromone and receptor genes in Neurospora differs between heterothallic and homothallic taxa, and among the homothallic lineages/clades previously indicated to represent independent switches from heterothallism to Homothallism in the evolutionary history of the genus. We complemented molecular evolution analyses with an expression study of the pre genes and their upstream regulators, the mating-type (mat) genes, in homothallic taxa. Our analyses suggest that the pheromone receptor gene pre-1 is functionally conserved in both heterothallic and homothallic taxa. Moreover, we found evidence of positive selection for a small fraction of codons in the cytoplasmic signal-transducing C-terminal region of the protein PRE-1. Distribution of positively selected codons differs between heterothallic and homothallic groups, suggesting functional divergence associated with mating system. The gene pre-2 was shown to evolve under high selective constraints, with no strong evidence for positive selection. Although our data suggest that both pre-1 and pre-2 are overall functional in homothallic taxa, individual taxa display frame-shift mutations causing premature stop codons, which might indicate loss of function. Transcriptional patterns of pre and mat genes in six homothallic taxa, selected to represent six different switches from heterothallism to Homothallism, do not support a universal pattern of regulation of these genes during reproductive tissue development. Taken together, our analyses suggest that the pheromone receptor genes pre-1 and pre-2 are in general functional in homothallic Neurospora taxa, in contrast with the situation for the mat genes that are generally degenerate in these taxa.
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A comprehensive phylogeny of Neurospora reveals a link between reproductive mode and molecular evolution in fungi.
Molecular phylogenetics and evolution, 2011Co-Authors: Kristiina Nygren, Rebecka Strandberg, Andreas Wallberg, Benoit Nabholz, Tim Gustafsson, Dania García, Jose M. Cano, Josep Guarro, Hanna JohannessonAbstract:The filamentous ascomycete genus Neurospora encompasses taxa with a wide range of reproductive modes. Sexual reproduction in this genus can be divided into three major modes; heterothallism (self-incompatibility), Homothallism (self-compatibility) and pseudoHomothallism (partial self-compatibility). In addition to the sexual pathway, most of the heterothallic taxa propagate with morphologically distinct, vegetative dissemination propagules (macroconidia), while this feature is undetected in the majority of the homothallic taxa. In this study, we used sequence information of seven nuclear gene loci from 43 taxa (295 of the possible 301 locus-by-taxon combinations) to create a phylogeny of Neurospora. The results suggest that transitions in reproductive mode have occurred at multiple times within this group of fungi. Although a homothallic ancestor would imply fewer switches in reproductive mode, we argue that the ancestor of Neurospora was likely heterothallic and that Homothallism has evolved independently at least six times in the evolutionary history of the genus. Furthermore, the two pseudohomothallic taxa of Neurospora (N. tetrasperma and N. tetraspora) represent two independent origins of pseudoHomothallism. Likelihood ratio tests of substitution rates among branches in the phylogeny indicate that reproductive mode is an important factor driving genome evolution in Neurospora. First, an increased level of non-synonymous/synonymous substitutions in branches delineating homothallic taxa was found, suggesting a reduced efficiency of purifying selection in these taxa. Furthermore, elevated nucleotide substitution rates were found in heterothallic, conidia-producing, lineages as compared to the homothallic non-conidiating lineages. The latter finding is likely due to the presence of conidia, i.e., a higher rate of mitotic divisions inducing mutations, and/or that the homothallic taxa have evolved a lower mutation rate to avoid genomic degeneration.
Miyuki Taniguchi - One of the best experts on this subject based on the ideXlab platform.
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Asd-Homothallism of Saccharomyces cerevisiae: identification of asd1-1 as an allele of sir4 and detection of α-specific suppressors of it
Current Genetics, 1993Co-Authors: Bun-ichiro Ono, Yumiko Ishino-arao, Miyuki TaniguchiAbstract:Asd-Homothallism of Saccharomyces cerevisiae involves a life cycle characterized by a non-mating phenotype and endomitotic diploidization. The former trait is determined by a single mutation, asd1-1 . This mutation was mapped between hom2 and lys4 on the right arm of chromosome IV and was complemented by the cloned SIR4 gene. Therefore, we conclude that asd1-1 is an allele of sir4-11 and renamed it sir4-11 . Endomitotic diploidization of asd-Homothallism is caused by the collaboration of three to four mutations including sir4-11 . In the course of this study, we detected α-specific suppressors of sir4-11 .
Joseph Heitman - One of the best experts on this subject based on the ideXlab platform.
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Multiple Pathways to Homothallism in Closely Related Yeast Lineages in the Basidiomycota.
mBio, 2021Co-Authors: Alexandra Cabrita, Joseph Heitman, Marco A Coelho, Márcia David-palma, Patrícia H. Brito, Paula GonçalvesAbstract:Sexual reproduction in fungi relies on proteins with well-known functions encoded by the mating type (MAT) loci. In the Basidiomycota, MAT loci are often bipartite, with the P/R locus encoding pheromone precursors and pheromone receptors and the HD locus encoding heterodimerizing homeodomain transcription factors (Hd1/Hd2). The interplay between different alleles of these genes within a single species usually generates at least two compatible mating types. However, a minority of species are homothallic, reproducing sexually without an obligate need for a compatible partner. Here, we examine the organization and function of the MAT loci of Cystofilobasidium capitatum, a species in the order Cystofilobasidiales, which is unusually rich in homothallic species. We determined MAT gene content and organization in C. capitatum and found that it resembles a mating type of the closely related heterothallic species Cystofilobasidium ferigula To explain the homothallic sexual reproduction observed in C. capitatum, we examined HD protein interactions in the two Cystofilobasidium species and determined C. capitatum MAT gene expression both in a natural setting and upon heterologous expression in Phaffia rhodozyma, a homothallic species belonging to a clade sister to that of Cystofilobasidium. We conclude that the molecular basis for Homothallism in C. capitatum appears to be distinct from that previously established for P. rhodozyma Unlike in the latter species, Homothallism in C. capitatum may involve constitutive activation or dispensability of the pheromone receptor and the functional replacement of the usual Hd1/Hd2 heterodimer by an Hd2 homodimer. Overall, our results suggest that Homothallism evolved multiple times within the Cystofilobasidiales.IMPORTANCE Sexual reproduction is important for the biology of eukaryotes because it strongly impacts the dynamics of genetic variation. In fungi, although sexual reproduction is usually associated with the fusion between cells belonging to different individuals (heterothallism), sometimes a single individual is capable of completing the sexual cycle alone (Homothallism). Homothallic species are unusually common in a fungal lineage named Cystofilobasidiales. Here, we studied the genetic bases of Homothallism in one species in this lineage, Cystofilobasidium capitatum, and found it to be different in several aspects from those of another homothallic species, Phaffia rhodozyma, belonging to the genus most closely related to Cystofilobasidium Our results strongly suggest that Homothallism evolved independently in Phaffia and Cystofilobasidium, lending support to the idea that transitions between heterothallism and Homothallism are not as infrequent as previously thought. Our work also helps to establish the Cystofilobasidiales as a model lineage in which to study these transitions.
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Multiple pathways to Homothallism in closely related yeast lineages in the Basidiomycota
2020Co-Authors: Alexandra Cabrita, Joseph Heitman, Marco A Coelho, Márcia David-palma, Patrícia H. Brito, Paula GonçalvesAbstract:Sexual reproduction in fungi relies on proteins with well-known functions encoded at the mating type (MAT) loci. In the Basidiomycota, MAT loci are often bipartite, the P/R locus encoding pheromone precursors and pheromone receptors and the HD locus encoding heterodimerizing homeodomain transcription factors (Hd1 and Hd2). The interplay between different alleles of these genes within a single species determines a variety of sexual systems and patterns, which may result in the emergence of hundreds of compatible mating types. However, a minority of species are homothallic, reproducing sexually without the need for a compatible partner. Here we examine the organization and function of the MAT loci of Cystofilobasidium capitatum, a species in the order Cystofilobasidiales, which is unusually rich in homothallic species. For this, we determined MAT gene content and organization in C. capitatum and found that it resembled a mating type of the closely related heterothallic species Cystofilobasidium ferigula. To explain the homothallic sexual reproduction observed in C. capitatum we examined HD -protein interactions in the two individual Cystofilobasidium species and determined C. capitatum MAT gene expression both in the natural setting and upon heterologous expression in Phaffia rhodozyma, a homothallic species belonging to a clade sister to the Cystofilobasidium. We conclude that the molecular basis for Homothallism in C. capitatum appears to be distinct from that previously established for P. rhodozyma. Unlike the latter species, Homothallism in C. capitatum may involve constitutive activation or dispensability of the pheromone receptor and the functional replacement of the usual Hd1/Hd2 heterodimer by an Hd2 homodimer. Overall, our results suggest that Homothallism evolved multiple times in the Cystofilobasidiales, underpinned by diverse molecular mechanisms.
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mating system evolution all roads lead to selfing
Current Biology, 2019Co-Authors: Marco A Coelho, Joseph HeitmanAbstract:Summary Fungi reproduce via both heterothallic outcrossing and homothallic selfing modes, and transitions between the two are common throughout the tree of life. A new study reports that the transition from heterothallism to Homothallism is common and has repeatedly punctuated the evolutionary trajectory across a major lineage of the fungal kingdom.
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Sexual Reproduction in Dermatophytes
Mycopathologia, 2017Co-Authors: Banu Metin, Joseph HeitmanAbstract:Sexual reproduction is a rich source of genetic variation and commonly observed among fungi. Basically two different modes of sexual reproduction are observed in fungi, namely heterothallism where two compatible mating types are required to undergo mating and Homothallism in which the organism is self-fertile. The genomic region governing the process of sexual reproduction and sex determination is called the mating type ( MAT ) locus. In filamentous ascomycetes including dermatophytes, the MAT locus harbors two different transcription factor genes in two different mating types. This review focuses on sexual reproduction and the structure of the MAT locus in dermatophytes. The reproductive modes and the observed mating types are summarized for different phylogenetic clades of dermatophytes. In addition, the question of whether or not unisexual reproduction, an interesting form of Homothallism, may be the sexual reproduction mode especially in anthropophilic dermatophytes is raised.
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Mechanisms of Homothallism in Fungi and Transitions between Heterothallism and Homothallism
Sex in Fungi, 2014Co-Authors: Xiaorong Lin, Joseph HeitmanAbstract:Sexual systems are classified into heterothallism or Homothallism in fungi. This chapter focuses on examples of homothallic fungi and how their sexuality is governed. Conversions between heterothallic and homothallic sexual cycles are common evolutionary transitions in fungi, and whether Homothallism evolved from heterothallism or vice versa is a controversial topic, and there is evidence supporting both hypotheses. The structural analyses of MAT sequences from homothallic and heterothallic Cochliobolus species support the hypothesis that heterothallism is the ancestral state in this genus. This unique arrangement of the Aspergillus nidulans MAT locus led to the proposal that Homothallism is the ancestral state and that a transition from Homothallism to heterothallism could have occurred in A. oryzae and A. fumigatus by gene loss, although neither species has a defined sexual cycle. Homothallic species may originate from heterothallic predecessors, and the homothallic lifestyle may have a selective advantage under certain ecological pressures. This hypothesis is consistent with the repeated occurrence of Homothallism within numerous genera and the fact that many heterothallic fungi achieve Homothallism in the form of pseudoHomothallism by mating-type switching or packaging two compatible nuclei into one spore. Homothallic individuals contain all of the necessary genetic information for full sexual expression.
Anastasia Gioti - One of the best experts on this subject based on the ideXlab platform.
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Deciphering the Relationship between Mating System and the Molecular Evolution of the Pheromone and Receptor Genes in Neurospora
Molecular biology and evolution, 2012Co-Authors: Kristiina Nygren, Anastasia Gioti, Rebecka Strandberg, Magnus Karlsson, Hanna JohannessonAbstract:Here, we present a study of the molecular evolution of the pheromone receptor genes (pre-1 and pre-2) in Neurospora taxa with different mating systems. We focus on comparisons between heterothallic and homothallic taxa, reproducing sexually by outcrossing and by intrahaploid selfing, respectively. Our general aim was to use a phylogenetic framework to investigate whether the evolutionary trajectory of the pheromone and receptor genes in Neurospora differs between heterothallic and homothallic taxa, and among the homothallic lineages/clades previously indicated to represent independent switches from heterothallism to Homothallism in the evolutionary history of the genus. We complemented molecular evolution analyses with an expression study of the pre genes and their upstream regulators, the mating-type (mat) genes, in homothallic taxa. Our analyses suggest that the pheromone receptor gene pre-1 is functionally conserved in both heterothallic and homothallic taxa. Moreover, we found evidence of positive selection for a small fraction of codons in the cytoplasmic signal-transducing C-terminal region of the protein PRE-1. Distribution of positively selected codons differs between heterothallic and homothallic groups, suggesting functional divergence associated with mating system. The gene pre-2 was shown to evolve under high selective constraints, with no strong evidence for positive selection. Although our data suggest that both pre-1 and pre-2 are overall functional in homothallic taxa, individual taxa display frame-shift mutations causing premature stop codons, which might indicate loss of function. Transcriptional patterns of pre and mat genes in six homothallic taxa, selected to represent six different switches from heterothallism to Homothallism, do not support a universal pattern of regulation of these genes during reproductive tissue development. Taken together, our analyses suggest that the pheromone receptor genes pre-1 and pre-2 are in general functional in homothallic Neurospora taxa, in contrast with the situation for the mat genes that are generally degenerate in these taxa.
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Unidirectional Evolutionary Transitions in Fungal Mating Systems and the Role of Transposable Elements
Molecular biology and evolution, 2012Co-Authors: Anastasia Gioti, Alexandra A. Mushegian, Rebecka Strandberg, Jason E. Stajich, Hanna JohannessonAbstract:The aim of this thesis was to study the evolution of reproductive systems and reproductive traits in the fungal genus Neurospora. More specifically, I have investigated the evolutionary forces shaping the genes involved in sexual reproduction, focusing on mating-type (mat) and pheromone receptor (pre) genes. Neurospora contains species exhibiting three different mating systems, i.e., heterothallism (self-incompatibility), Homothallism (self-compatibility) and pseudoHomothallism (partial self-incompatibility). First, a robust phylogeny of Neurospora was established. The phylogenetic analyses revealed multiple independent transitions in reproductive life style during the evolutionary history of the genus. We argued for a heterothallic ancestor of the genus, although our subsequent ancestral reconstruction analyses favored a homothallic ancestor. To be able to settle the ancestral mating system, we zoomed in on the structural architecture of the mat-locus in four homothallic species of Neurospora, thought to have arisen from independent transitions. Our results led us to suggest two different genetic mechanisms (translocation and unequal crossover) to explain the transitions in mating system from heterothallism to Homothallism. We pointed out that the mating-system transitions in Neurospora are unidirectional, and suggested that transposable elements might be driving the transitions. In conclusion, we suggest a heterothallic ancestor for Neurospora, and that at least six transitions to Homothallism and two transitions to pseudoHomothallism have occurred in its evolutionary history. Further, we used the phylogeny of Neurospora as a framework to test if the evolution of pre-genes (pre-1 and pre-2) in hetero- and homothallic Neurospora is dependent on mating systems and/or even the homothallic clades themselves (i.e., mating-system and/or switch-dependent). The molecular evolution results suggest that pre-1 and pre-2 are overall functional in both homothallic and heterothallic Neurospora. The molecular evolution of pre-1 seems to be independent of mating-system or homothallic clade, and we detected signs for positive selection in the C-terminal tail. For pre-2 we found no support for mating-system dependent evolution, but indications for switch-dependent evolution. In this study we also included expression analyses of both pre- as well as mat-genes, with the prospect to assess functionality and regulation. During this thesis work, we also performed a phylogenetic study were we found that reproductive genes might be more permeable to introgression than other genes, which is in contrast to theoretical expectations. In the last study, we confirmed the co-existence of two alternative splice variants of the pheromone receptor gene pre-1 in Neurospora crassa, and performed expression profiles studies using quantitative RT-PCR. I hope this thesis work will further strengthen Neurospora as a model for research in evolutionary genetics.
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Research article Unidirectional Evolutionary Transitions in Fungal Mating Systems and the Role of Transposable Elements
2012Co-Authors: Anastasia Gioti, Alexandra A. Mushegian, Rebecka Strandberg, Jason E. Stajich, Hanna JohannessonAbstract:In the fungal kingdom, the evolution of mating systems is highly dynamic, varying even among closely related species. Rearrangements in the mating-type (mat) locus, which contains the major regulators of sexual development, are expected to underlie the transitions between self-sterility (heterothallism) and self-fertility (Homothallism). However, both the genetic mechanisms and the direction of evolutionary transitions in fungal mating systems are under debate. Here, we present new sequences of the mat locus of four homothallic and one heterothallic species of the model genus Neurospora (Ascomycota). By examining the patterns of synteny among these sequences and previously published data, we show that the locus is conserved among heterothallic species belonging to distinct phylogenetic clades, while different gene arrangements characterize the four homothallic species. These results allowed us to ascertain a heterothallic ancestor for the genus, confirming the prediction of the dead-end theory on unidirectional transitions toward selfing. We show that at least four shifts from heterothallism to Homothallism have occurred in Neurospora, three of which involve the acquisition of sequences of both mating types into the same haploid genome. We present evidence for two genetic mechanisms allowing these shifts: translocation and unequal crossover. Finally, we identified two novel retrotransposons and suggest that these have played a major role in mating-system transitions, by facilitating multiple rearrangements of the mat locus.
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Research article Deciphering the Relationship between Mating System and the Molecular Evolution of the Pheromone and Receptor Genes in Neurospora
2012Co-Authors: Kristiina Nygren, Anastasia Gioti, Rebecka Strandberg, Magnus Karlsson, Hanna JohannessonAbstract:Here, we present a study of the molecular evolution of the pheromone receptor genes (pre-1 and pre-2 )i nNeurospora taxa with different mating systems. We focus on comparisons between heterothallic and homothallic taxa, reproducing sexually by outcrossing and by intrahaploid selfing, respectively. Our general aim was to use a phylogenetic framework to investigate whether the evolutionary trajectory of the pheromone and receptor genes in Neurospora differs between heterothallic and homothallic taxa, and among the homothallic lineages/clades previously indicated to represent independent switches from heterothallism to Homothallism in the evolutionary history of the genus. We complemented molecular evolution analyses with an expression study of the pre genes and their upstream regulators, the mating-type (mat) genes, in homothallic taxa. Our analyses suggest that the pheromone receptor gene pre-1 is functionally conserved in both heterothallic and homothallic taxa. Moreover, we found evidence of positive selection for a small fraction of codons in the cytoplasmic signal-transducing C-terminal region of the protein PRE-1. Distribution of positively selected codons differs between heterothallic and homothallic groups, suggesting functional divergence associated with mating system. The gene pre-2 was shown to evolve under high selective constraints, with no strong evidence for positive selection. Although our data suggest that both pre-1 and pre-2 are overall functional in homothallic taxa, individual taxa display frame-shift mutations causing premature stop codons, which might indicate loss of function. Transcriptional patterns of pre and mat genes in six homothallic taxa, selected to represent six different switches from heterothallism to Homothallism, do not support a universal pattern of regulation of these genes during reproductive tissue development. Taken together, our analyses suggest that the pheromone receptor genes pre-1 and pre-2 are in general functional in homothallic Neurospora taxa, in contrast with the situation for the mat genes that are generally degenerate in these taxa.
M. Taniguchi - One of the best experts on this subject based on the ideXlab platform.
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Asd-Homothallism of Saccharomyces cerevisiae: identification of asd1-1 as an allele of sir4 and detection of alpha-specific suppressors of it.
Current genetics, 1993Co-Authors: B Ono, Y Ishino-arao, M. TaniguchiAbstract:Asd-Homothallism of Saccharomyces cerevisiae involves a life cycle characterized by a non-mating phenotype and endomitotic diploidization. The former trait is determined by a single mutation, asd1-1. This mutation was mapped between hom2 and lys4 on the right arm of chromosome IV and was complemented by the cloned SIR4 gene. Therefore, we conclude that asd1-1 is an allele of sir4-11 and renamed it sir4-11. Endomitotic diploidization of asd-Homothallism is caused by the collaboration of three to four mutations including sir4-11. In the course of this study, we detected alpha-specific suppressors of sir4-11.