scholarly journals Pseudohomothallism and Evolution of the Mating-Type Chromosome in Neurospora tetrasperma

Genetics ◽  
1996 ◽  
Vol 143 (2) ◽  
pp. 789-799 ◽  
Author(s):  
Sandra T Merino ◽  
Mary Anne Nelson ◽  
David J Jacobson ◽  
Donald O Natvig
Keyword(s):  
Genetic Variability ◽  
Mating Type ◽  
High Frequency ◽  
Population Biology ◽  
Unexpected Result ◽  
Evolutionary Time ◽  
Distinct Haplotype ◽  
Suppressed Recombination ◽  
Neurospora Tetrasperma ◽  
Type Chromosome

Abstract Ascospores of Neurospora tetrasperma normally contain nuclei of both mating-type idiomorphs (a and A), resulting in self-fertile heterokaryons (a type of sexual reproduction termed pseudohomothallism). Occasional homokaryotic self-sterile strains (either a or A) behave as heterothallics and, in principle, provide N. tetrasperma with a means for facultative outcrossing. This studywas conceived as an investigation of the population biology of N. tetrasperma to assess levels of intrastrain heterokaryosis (heterozygosity). The unexpected result was that the mating-type chromosome and autosomes exhibited very different patterns of evolution, apparently because of suppressed recombination between mating-type chromosomes. Analysis of sequences on the mating-type chromosomes of wild-collected self-fertile strains revealed high levels of genetic variability between sibling A and a nuclei. In contrast, sequences on autosomes of sibling A and a nuclei exhibited nearly complete homogeneity. Conservation of distinct haplotype combinations on A and a mating-type chromosomes in strains from diverse locations further suggested an absence of recombination over substantial periods of evolutionary time. The suppression of recombination on the N. tetrasperma mating-type chromosome, expected to ensure a high frequency of self fertility, presents an interesting parallel with, and possible model for studying aspects of, the evolution of mammalian sex chromosomes.

scholarly journals Suppressed Recombination and a Pairing Anomaly on the Mating-Type Chromosome of Neurospora tetrasperma

Genetics ◽  
2000 ◽  
Vol 154 (2) ◽  
pp. 623-633 ◽  
Author(s):  
Alena Gallegos ◽  
David J Jacobson ◽  
Namboori B Raju ◽  
Marian P Skupski ◽  
Donald O Natvig
Keyword(s):  
Mating Type ◽  
Mitotic Division ◽  
Crossing Over ◽  
Unpaired Region ◽  
Wild Strains ◽  
Suppressed Recombination ◽  
Pseudoautosomal Regions ◽  
Neurospora Tetrasperma ◽  
Type Chromosome ◽  
Chromosome Disjunction

Abstract Neurospora crassa and related heterothallic ascomycetes produce eight homokaryotic self-sterile ascospores per ascus. In contrast, asci of N. tetrasperma contain four self-fertile ascospores each with nuclei of both mating types (matA and mata). The self-fertile ascospores of N. tetrasperma result from first-division segregation of mating type and nuclear spindle overlap at the second meiotic division and at a subsequent mitotic division. Recently, Merino et al. presented population-genetic evidence that crossing over is suppressed on the mating-type chromosome of N. tetrasperma, thereby preventing second-division segregation of mating type and the formation of self-sterile ascospores. The present study experimentally confirmed suppressed crossing over for a large segment of the mating-type chromosome by examining segregation of markers in crosses of wild strains. Surprisingly, our study also revealed a region on the far left arm where recombination is obligatory. In cytological studies, we demonstrated that suppressed recombination correlates with an extensive unpaired region at pachytene. Taken together, these results suggest an unpaired region adjacent to one or more paired regions, analogous to the nonpairing and pseudoautosomal regions of animal sex chromosomes. The observed pairing and obligate crossover likely reflect mechanisms to ensure chromosome disjunction.

scholarly journals Degeneration in Codon Usage within the Region of Suppressed Recombination in the Mating-Type Chromosomes of Neurospora tetrasperma

2011 ◽  
Vol 10 (4) ◽  
pp. 594-603 ◽  
Author(s):  
C. A. Whittle ◽  
Y. Sun ◽  
H. Johannesson
Keyword(s):  
Codon Usage ◽  
Mating Type ◽  
Chromosome Evolution ◽  
Sex Chromosome ◽  
Sex Chromosome Evolution ◽  
Recombination Suppression ◽  
Content Type ◽  
Genomic Changes ◽  
Suppressed Recombination ◽  
Neurospora Tetrasperma

ABSTRACT The origin and early evolution of sex chromosomes are currently poorly understood. The Neurospora tetrasperma mating-type ( mat ) chromosomes have recently emerged as a model system for the study of early sex chromosome evolution, since they contain a young (<6 million years ago [Mya]), large (>6.6-Mb) region of suppressed recombination. Here we examined preferred-codon usage in 290 genes (121,831 codon positions) in order to test for early signs of genomic degeneration in N. tetrasperma mat chromosomes. We report several key findings about codon usage in the region of recombination suppression, including the following: (i) this region has been subjected to marked and largely independent degeneration among gene alleles; (ii) the level of degeneration is magnified over longer periods of recombination suppression; and (iii) both mat a and mat A chromosomes have been subjected to deterioration. The frequency of shifts from preferred codons to nonpreferred codons is greater for shorter genes than for longer genes, suggesting that short genes play an especially significant role in early sex chromosome evolution. Furthermore, we show that these degenerative changes in codon usage are best explained by altered selection efficiency in the recombinationally suppressed region. These findings demonstrate that the fungus N. tetrasperma provides an effective system for the study of degenerative genomic changes in young regions of recombination suppression in sex-regulating chromosomes.

scholarly journals Sex-linked transcriptional divergence in the hermaphrodite fungus Neurospora tetrasperma

2013 ◽  
Vol 280 (1764) ◽  
pp. 20130862 ◽  
Author(s):  
Nicklas Samils ◽  
Anastasia Gioti ◽  
Magnus Karlsson ◽  
Yu Sun ◽  
Takao Kasuga ◽  
...  
Keyword(s):  
Mating Type ◽  
Sequence Divergence ◽  
Differentially Expressed ◽  
Female Development ◽  
Molecular Phenotype ◽  
Filamentous Ascomycete ◽  
Agar Media ◽  
Suppressed Recombination ◽  
Neurospora Tetrasperma ◽  
Male Tissue

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.

scholarly journals Evolutionary strata on young mating-type chromosomes despite the lack of sexual antagonism

2017 ◽  
Vol 114 (27) ◽  
pp. 7067-7072 ◽  
Author(s):  
Sara Branco ◽  
Hélène Badouin ◽  
Ricardo C. Rodríguez de la Vega ◽  
Jérôme Gouzy ◽  
Fantin Carpentier ◽  
...  
Keyword(s):  
Mating Type ◽  
Balancing Selection ◽  
Smut Fungi ◽  
Mating Types ◽  
Sexual Antagonism ◽  
Recombination Suppression ◽  
Ancestral Gene ◽  
Anther Smut ◽  
Mating Type Genes ◽  
Suppressed Recombination

Sex chromosomes can display successive steps of recombination suppression known as “evolutionary strata,” which are thought to result from the successive linkage of sexually antagonistic genes to sex-determining genes. However, there is little evidence to support this explanation. Here we investigate whether evolutionary strata can evolve without sexual antagonism using fungi that display suppressed recombination extending beyond loci determining mating compatibility despite lack of male/female roles associated with their mating types. By comparing full-length chromosome assemblies from five anther-smut fungi with or without recombination suppression in their mating-type chromosomes, we inferred the ancestral gene order and derived chromosomal arrangements in this group. This approach shed light on the chromosomal fusion underlying the linkage of mating-type loci in fungi and provided evidence for multiple clearly resolved evolutionary strata over a range of ages (0.9–2.1 million years) in mating-type chromosomes. Several evolutionary strata did not include genes involved in mating-type determination. The existence of strata devoid of mating-type genes, despite the lack of sexual antagonism, calls for a unified theory of sex-related chromosome evolution, incorporating, for example, the influence of partially linked deleterious mutations and the maintenance of neutral rearrangement polymorphism due to balancing selection on sexes and mating types.

scholarly journals Asexual Propagation of a Virulent Clone Complex in a Human and Feline Outbreak of Sporotrichosis

2014 ◽  
Vol 14 (2) ◽  
pp. 158-169 ◽  
Author(s):  
Marcus de Melo Teixeira ◽  
Anderson Messias Rodrigues ◽  
Clement K. M. Tsui ◽  
Luiz Gonzaga Paulo de Almeida ◽  
Anne D. Van Diepeningen ◽  
...  
Keyword(s):  
Genetic Variability ◽  
Mating Type ◽  
Sequence Data ◽  
Fungal Infections ◽  
Haplotype Diversity ◽  
Sporothrix Schenckii ◽  
Mitogen Activated Protein Kinase ◽  
Comparative Genomic ◽  
Asexual Propagation ◽  
Content Type

ABSTRACT Sporotrichosis is one of the most frequent subcutaneous fungal infections in humans and animals caused by members of the plant-associated, dimorphic genus Sporothrix . Three of the four medically important Sporothrix species found in Brazil have been considered asexual as no sexual stage has ever been reported in Sporothrix schenckii , Sporothrix brasiliensis , or Sporothrix globosa . We have identified the mating type ( MAT ) loci in the S. schenckii (strain 1099-18/ATCC MYA-4821) and S. brasiliensis (strain 5110/ATCC MYA-4823) genomes by using comparative genomic approaches to determine the mating type ratio in these pathogen populations. Our analysis revealed the presence of a MAT1-1 locus in S. schenckii while a MAT1-2 locus was found in S. brasiliensis representing genomic synteny to other Sordariomycetes . Furthermore, the components of the mitogen-activated protein kinase (MAPK)-pheromone pathway, pheromone processing enzymes, and meiotic regulators have also been identified in the two pathogens, suggesting the potential for sexual reproduction. The ratio of MAT1-1 to MAT1-2 was not significantly different from 1:1 for all three Sporothrix species, but the population of S. brasiliensis in the outbreaks originated from a single mating type. We also explored the population genetic structure of these pathogens using sequence data of two loci to improve our knowledge of the pattern of geographic distribution, genetic variation, and virulence phenotypes. Population genetics data showed significant population differentiation and clonality with a low level of haplotype diversity in S. brasiliensis isolates from different regions of sporotrichosis outbreaks in Brazil. In contrast, S. schenckii isolates demonstrated a high degree of genetic variability without significant geographic differentiation, indicating the presence of recombination. This study demonstrated that two species causing the same disease have contrasting reproductive strategies and genetic variability patterns.

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