Heterokaryosis in Gibberella zeae varies depending upon the compatibility of the fused strains an... more Heterokaryosis in Gibberella zeae varies depending upon the compatibility of the fused strains and the manner in which the strains are fused. Analysis of nutritionally complementing auxotrophic markers in pairings via hyphal anastamoses revealed a nuclear distribution in which ...
The idealized individual in many fungal species is a haploid self-sterile hermaphrodite that may ... more The idealized individual in many fungal species is a haploid self-sterile hermaphrodite that may be propagated by asexually produced spores or that may reproduce sexually. In field populations, polymorphism occurs for female-sterile/ hermaphrodite status, and female-sterile mutants, which function only as males during sexual reproduction, may comprise >50% of the population. The effective population number may be based on the number of strains of different mating type or the relative frequency of hermaphrodites. The female-sterile mutants are at a selective disadvantage every time sexual reproduction occurs, and must have an advantage during vegetative propagation to persist at a significant frequency. When a high frequency of female-sterile strains is observed in field populations, it indicates that vegetative propagation is a significant component of the fungus' natural history. Depending on the mutation rate to female sterility and the selective advantage of the femalesterile strains during vegetative propagation, the ratio of sexua1:asexual generations can range from 1:15 to 1:2300 for species in the Gibberellafujzkuroi complex. The relative rarity of sexual reproduction may permit female-sterile strains to accumulate to a level such that local populations could completely lose sexuality and appear as asexual (imperfect) species.
Comparisons of draft genome sequences of three geographically distinct isolates of Fusarium fujik... more Comparisons of draft genome sequences of three geographically distinct isolates of Fusarium fujikuroi with two recently published genome sequences from the same species suggest diverse profiles of secondary metabolite production within F. fujikuroi. Speciesand lineage-specific genes, many of which appear to exhibit expression profiles that are consistent with roles in host-pathogen interactions and adaptation to environmental changes, are concentrated in subtelomeric regions. These genomic compartments also exhibit distinct gene densities and compositional characteristics with respect to other genomic partitions, and likely play a role in the generation of molecular diversity. Our data provide additional evidence that gene duplication, divergence, and differential loss play important roles in F. fujikuroi genome evolution and suggest that hundreds of lineage-specific genes might have been acquired through horizontal gene transfer.
We constructed a recombination-based map of the fungal plant pathogen Gibberellafujikuroi mating ... more We constructed a recombination-based map of the fungal plant pathogen Gibberellafujikuroi mating population A (asexual stage Fusarium moniliforme). The map is based on the segregation of 142 restriction fragment length polymorphism (RFLP) markers, two auxotrophic genes (argl, n i c l) , mating type (matA+/matA-), female sterility (stel), spore-killer (S k) , and a gene governing the production of the mycotoxin fumonisin B1 (f u m l) among 121 random ascospore progeny from a single cross. We identified 12 linkage groups corresponding to the 12 chromosome-sized DNAs previously observed in contourclamped homogeneous electric field (CHEF) gels. Linkage groups and chromosomes were correlated via Southern blots between appropriate RFLP markers and the CHEF gels. Eleven of the 12 chromosomes are meiotically stable, but the 12th (and smallest) is subject to deletions in 3% (4/121) of the progeny. Positive chiasma interference occurred on five of the 12 chromosomes, and nine of the 12 chromosomes averaged more than one crossover per chromosome. The average kb/cM ratio in this cross is-32.
Kansas and California wheat-growing regions differ dramatically in soils, climate, wheat cultivar... more Kansas and California wheat-growing regions differ dramatically in soils, climate, wheat cultivars, crop rotation patterns, and cultural practices, which could select for different fungal populations of Mycosphaerella graminicola. Our objective in this study was to use amplified fragment length polymorphism (AFLP) loci to assess the genetic diversity of M. graminicola populations within single fields in two widely separated, and geographically isolated sites in Kansas and California. Three primer-pair combinations were used to resolve polymorphism at 177 loci in 67 and 63 isolates from Kansas and California, respectively. Genotypic variability was high, which is consistent with a genetically diverse initial inoculum. There was no evidence of genetic disequilibrium in either population, with only 4.6% of the locus pairs in Kansas, and 5.4% of the locus pairs in California in detectable disequilibrium. The migration rate calculated between the two sites was as low as 1.8 individuals per generation, and significant differences in allele frequencies were observed. Therefore, these two populations do not represent mere subsamples of a larger, randomly mating population. This is a rare report of isolation by distance occurring between two North American populations of M. graminicola, indicating that at least some of these populations may be differentiating. Although genetic isolation by distance may occur, we cannot exclude movement of new gene combinations such as fungicide resistance or virulence between these two locations.
Wild-collected isolates of Neurospora crassa Shear and Dodge were systematically examined for rec... more Wild-collected isolates of Neurospora crassa Shear and Dodge were systematically examined for recessive mutations affecting the sexual phase of the life cycle, which is essentially diploid. Seventy-four of 99 wild-collected isolates from 26 populations in the United States, India and Pakistan carried one or more recessive mutations that reduced fertility significantly when homozygous; mutations affecting spore morphology were also detected. Limited complementation tests indicate that most of the 106 recovered mutations are unique.-T h e recessive diplophase (= sexual phase) mutations were uncovered by crossing each wild-collected isolate to a marked two-chromosome double-reciprocal translocation strain as "balancer." Surviving progeny receive approximately 60% of their genome from the wild parent, but receive the mating-type allele from the "balancer" parent. These progeny were backcrossed to the wild parent and were also crossed with a standard laboratory strain (fl). Reduced fertility in the backcross us. normal fertility in the cross with the laboratory standard signals the presence of a recessive mutation in the wild-collected isolate.-Most of the mutants (95 of 106) fall into two major classes: those producing barren perithecia with no or few viable ascospores (51) and those with spore maturation defects (44). Most of the recessive barrens result either from an early block in meiosis o r ascus development (25) o r from a late disturbance in postmeiotic ascus behavior (1 8).-These recessive mutations are formally equivalent to recessive lethals in higher eukaryotes and may be important in determining the breeding structure of natural Neurospora populations. EUROSPORA crassa Shear and Dodge is genetically and biochemically one of the most intensively studied eukaryotic microbes, but little was known of natural Neurospora populations until systematic collections were begun in 1969 (PERKINS, TURNER and BARRY 1976). Wild-collected Neurospora have since been examined for electrophoretic enzyme polymorphisms (SPIETH 1975), Spore killers (a meiotic drive phenomenon, TURNER and PERKINS 1979), vegetative (heterokaryon) incompatibility (MYLYK 1976), variations in ribosomal DNA organization (RUSSELL et al. 1984), DNA restriction fragment length polymorphisms (METZENBERG et al. 1984) and mitochondrial DNA composition ' To whom correspondence should be addressed.
Genetic maps are useful for researchers outside the originating laboratory only if the strains an... more Genetic maps are useful for researchers outside the originating laboratory only if the strains and markers used in the analysis of the mapping population and the genotypes of the strains composing the mapping population are available for analysis. This brief communication gives the genotypes for the strains that compose a recently constructed mapping population of G. fujikuroi. Strains and probes are available from FGSC.
Frontiers in sustainable food systems, Jan 27, 2023
Mycotoxins, such as aflatoxins, fumonisins, trichothecenes, and zearalenone, are increasing in vi... more Mycotoxins, such as aflatoxins, fumonisins, trichothecenes, and zearalenone, are increasing in visibility as a public health threat through both acute and chronic exposure in food. USAID through its Feed the Future program has sponsored research in Nepal on mycotoxin contamination and the correlated high levels of stunting in children under age five. Communicating about mycotoxins is a complicated matter, as is communicating about any potentially serious economic or health threat that may be di cult to control. Two nominal group workshops in Nepal focused on identifying problems from multiple perspectives and developing potential communication strategies to mitigate the problem and potential concerns about it. Target audiences were identified along with their interests and e ective channels to communicate with and within them. The first audience to work with is the government, as it must understand and value the problem and help generate confidence in potential regulatory and mitigation processes. Producers, educators and health professionals are the next audiences to address as they are the most closely involved with the problem. Consumer engagement is last, with a communication goal of sharing information to heighten awareness and minimize unwarranted public concern.
The polymerase chain reaction (PCR) is a method for amplifying specific segments of DNA defined b... more The polymerase chain reaction (PCR) is a method for amplifying specific segments of DNA defined by the small primers used to start the reaction. Using arbitrarily chosen 10-base primers, one can generate "random amplified polymorphic DNA" (RAPD) markers (Williams et al. 1991 Nucl. Acids Res. 18:6531-6535). These DNA fragments, separated by electrophoresis in an agarose gel, can be used as markers for studying genetic variation within and among fungal populations.
Gibberella fujikuroi and Gibberella intermedia (mating populations 'C' and 'D' of the G. fujikuro... more Gibberella fujikuroi and Gibberella intermedia (mating populations 'C' and 'D' of the G. fujikuroi species complex) can be distinguished by differences in the spectrum of mycotoxins produced, the lack of sexual cross-fertility and diagnostic differences in their DNA sequences. Some isolates from these two biological species, however, can interbreed and complete meiosis to produce viable progeny. Analysis of marker segregation amongst such hybrid progeny can be used to estimate the degree of genomic rearrangement and genetic incompatibility that has accumulated since these sibling species diverged. Recombinant progeny were isolated from crosses of the standard tester strains for these two species and from crosses between these standard testers and a field isolate (KSU X-10626) that was cross-fertile with tester strains of both species. Progeny in all of the crosses segregated for amplified fragment length polymorphisms (AFLPs). Segregation of AFLP loci deviated from 1:1 for two thirds of the loci amongst the progeny of the cross between the 'C' and 'D' mating population tester strains, but <20% of the polymorphic loci in the cross of either tester with KSU X-10626 showed such distortion. It was concluded that G. intermedia and G. fujikuroi are sufficiently interfertile to belong to the same biological species, but that changing the nomenclature to reflect this interfertility requires more evidence for the natural occurrence of a continuum in fertility than is presently available.
Gene conversion causes deviations from the 2:2 segregation of allele pairs in meiosis. Thus, gene... more Gene conversion causes deviations from the 2:2 segregation of allele pairs in meiosis. Thus, gene co'nversion is a potential cause for changes of allele frequencies in populations. Equations are derived for the effects of conversion in a large random-mating population. The influence of gene conversion on allele frequencies is compared with that of spontaneous mutation and meiotic drive.
THIL;VL;IIR;VR) BLNC-1 is a compound chromosome rearrangement in Neurospora crassa that combines ... more THIL;VL;IIR;VR) BLNC-1 is a compound chromosome rearrangement in Neurospora crassa that combines two reciprocal translocations: T(IIL; VL) A R30 which interchb.nges the left end of linkage group II with the left end of linkage group V, and T(IIR;VR) ALSI54 which interchanges the right end of linkage group II with the right end of linkage group V. BLNC-I acts as a crossover suppressor for most of both linkage groups II and V since single crossovers between the rearrangement breakpoints result in progeny with lethal unbalanced duplications and deficiencies. The integrity of BLNC-I following meiosis was tested in crosses of marked BLNC-I by marked Normal sequence, with markers located at critical points on linkage groups I1 and V. Although recombination between distal markers in the four arms was reduced markedly, double crossovers in the long intervening regions occurred with a frequency of 21%. Of these double crossovers, most were coincidental crossovers, one in each of the long intervening regions, resulting in the resolution of the complex into its component rearrangements (16%), while a minority of the double crossovers (5%) were crossovers involving only one of the two component linkage groups, and resulted in the insertion of a segment between the breakpoints.-The BLNC-1 balancer can be used for: (1) mapping new loci to linkage groups II and V, especially for identifying markers mapping near the tips of the linkage groups; (2) for isolating genetically intact chromosomes from natural populations or for quantitative genetic studies; and (3) for studying recombinational hot-spots which can be detected as escapes from crossover suppression.-Based on experience with BLNC-I, future two-chromosome balancers should be designed with two breakpoints near, but not at, the opposite ends of the chromosome to be balanced, and the other two breakpoints close to, but spanning, the centromere of a second chromosome. Such a construction when combined with appropriately placed selective markers should prevent breakdown of the complex, and should resemble an inversion in eliminating crossover products.
It has never been determined in Neurospora whether multiple alleles exist at individual het loci ... more It has never been determined in Neurospora whether multiple alleles exist at individual het loci such that interaction between any two unlike alleles will result in an incompatibility reaction. The evidence summarized here from recombination genetics and from sampling natural populations suggests multiple allelism at two of the best studied het loci. However, an alternate explanation is not excluded that invokes linked multiple loci rather than multiple alleles.
The regulatory gene nit-2 of Neurospora crassa complements a nnu mutant of Gibberella zeae (Fusar... more The regulatory gene nit-2 of Neurospora crassa complements a nnu mutant of Gibberella zeae (Fusarium graminearum
Chromosome rearrangements between fungal strains may reduce fertility in sexual crosses through t... more Chromosome rearrangements between fungal strains may reduce fertility in sexual crosses through the production of genetically inviable recombinant progeny. As such, rearrangements can be important postzygotic reproductive barriers that contribute to the speciation process. The presence of chromosome rearrangements in crosses with Gibberella zeae was tested by counting asci with 8, 6, 4, or 2 viable ascospores. Counts were made by observing rosettes of asci extruded from crushed perithecia and by observing unordered ascospore tetrads ejected onto agar slabs from mature perithecia. The two methods gave similar results. Self-fertilized cultures served as controls and produced the normal eight ascospores per ascus in >98% of cases. Crosses with strains known to carry chromosome rearrangements produced significant frequencies of asci with 6, 4, or 2 ascospores, as expected. These results suggest that these methods will be useful to survey populations of G. zeae for chromosome rearrangements.
Canadian journal of genetics and cytology, Dec 1, 1982
In ln(IL; IR)OY323 of Neurospora crassa, a long central segment of linkage group I is inverted th... more In ln(IL; IR)OY323 of Neurospora crassa, a long central segment of linkage group I is inverted that includes the centromere. This is the first interstitial pericentric inversion to be identified in a fungus. In genetic and cytological behavior, it resembles chromosome inversions in higher eukaryotes. In crosses heterozygous for the OY323 inversion, normally distant markers are closely linked, while in homozygous inversion crosses the gene order is reversed, but recombination is approximately normal within the inverted segment. A characteristic inversion loop may form at pachytene in heterozygous crosses; frequently, segments distal to the breakpoints do not pair, however. Rearrangement breakpoints were mapped precisely by duplication coverage using appropriate recessive markers in crosses of OY323 with a partially overlapping inversion, In(IL→IR)NM176.
The initiation of monokaryotic fruiting in the basidiomycetous fungus Schizophyllum commune has b... more The initiation of monokaryotic fruiting in the basidiomycetous fungus Schizophyllum commune has been observed to occur spontaneously, in response to biochemical substances, and following mechanical injury. The responses to these three stimuli are genetically separable and under polygenic control.
Fusarium subglutinans and F. temperatum are two important fungal pathogens of maize whose distinc... more Fusarium subglutinans and F. temperatum are two important fungal pathogens of maize whose distinctness as separate species has been difficult to assess. We isolated strains of these species from commercial and native maize varieties in Argentina and sequenced >28,000 loci to estimate genetic variation in the sample. Our objectives were to measure genetic divergence between the species, infer demographic parameters related to their split, and describe the population structure of the sample. When analyzed together, over 30% of each species’ polymorphic sites (>2,500 sites) segregate as polymorphisms in the other. Demographic modeling confirmed the species split predated maize domestication, but subsequent between-species gene flow has occurred, with gene flow from F. subglutinans into F. temperatum greater than gene flow in the reverse direction. In F. subglutinans, little evidence exists for substructure or recent selective sweeps, but there is evidence for limited sexual repro...
Members of the fungal genus Fusarium can produce numerous secondary metabolites, including the no... more Members of the fungal genus Fusarium can produce numerous secondary metabolites, including the nonribosomal mycotoxins beauvericin (BEA) and enniatins (ENNs). Both mycotoxins are synthesized by the multifunctional enzyme enniatin synthetase (ESYN1) that contains both peptide synthetase and S-adenosyl-l-methionine-dependent N-methyltransferase activities. Several Fusarium species can produce ENNs, BEA or both, but the mechanism(s) enabling these differential metabolic profiles is unknown. In this study, we analyzed the primary structure of ESYN1 by sequencing esyn1 transcripts from different Fusarium species. We measured ENNs and BEA production by ultra-performance liquid chromatography coupled with photodiode array and Acquity QDa mass detector (UPLC-PDA-QDa) analyses. We predicted protein structures, compared the predictions by multivariate analysis methods and found a striking correlation between BEA/ENN-producing profiles and ESYN1 three-dimensional structures. Structural differe...
Heterokaryosis in Gibberella zeae varies depending upon the compatibility of the fused strains an... more Heterokaryosis in Gibberella zeae varies depending upon the compatibility of the fused strains and the manner in which the strains are fused. Analysis of nutritionally complementing auxotrophic markers in pairings via hyphal anastamoses revealed a nuclear distribution in which ...
The idealized individual in many fungal species is a haploid self-sterile hermaphrodite that may ... more The idealized individual in many fungal species is a haploid self-sterile hermaphrodite that may be propagated by asexually produced spores or that may reproduce sexually. In field populations, polymorphism occurs for female-sterile/ hermaphrodite status, and female-sterile mutants, which function only as males during sexual reproduction, may comprise >50% of the population. The effective population number may be based on the number of strains of different mating type or the relative frequency of hermaphrodites. The female-sterile mutants are at a selective disadvantage every time sexual reproduction occurs, and must have an advantage during vegetative propagation to persist at a significant frequency. When a high frequency of female-sterile strains is observed in field populations, it indicates that vegetative propagation is a significant component of the fungus' natural history. Depending on the mutation rate to female sterility and the selective advantage of the femalesterile strains during vegetative propagation, the ratio of sexua1:asexual generations can range from 1:15 to 1:2300 for species in the Gibberellafujzkuroi complex. The relative rarity of sexual reproduction may permit female-sterile strains to accumulate to a level such that local populations could completely lose sexuality and appear as asexual (imperfect) species.
Comparisons of draft genome sequences of three geographically distinct isolates of Fusarium fujik... more Comparisons of draft genome sequences of three geographically distinct isolates of Fusarium fujikuroi with two recently published genome sequences from the same species suggest diverse profiles of secondary metabolite production within F. fujikuroi. Speciesand lineage-specific genes, many of which appear to exhibit expression profiles that are consistent with roles in host-pathogen interactions and adaptation to environmental changes, are concentrated in subtelomeric regions. These genomic compartments also exhibit distinct gene densities and compositional characteristics with respect to other genomic partitions, and likely play a role in the generation of molecular diversity. Our data provide additional evidence that gene duplication, divergence, and differential loss play important roles in F. fujikuroi genome evolution and suggest that hundreds of lineage-specific genes might have been acquired through horizontal gene transfer.
We constructed a recombination-based map of the fungal plant pathogen Gibberellafujikuroi mating ... more We constructed a recombination-based map of the fungal plant pathogen Gibberellafujikuroi mating population A (asexual stage Fusarium moniliforme). The map is based on the segregation of 142 restriction fragment length polymorphism (RFLP) markers, two auxotrophic genes (argl, n i c l) , mating type (matA+/matA-), female sterility (stel), spore-killer (S k) , and a gene governing the production of the mycotoxin fumonisin B1 (f u m l) among 121 random ascospore progeny from a single cross. We identified 12 linkage groups corresponding to the 12 chromosome-sized DNAs previously observed in contourclamped homogeneous electric field (CHEF) gels. Linkage groups and chromosomes were correlated via Southern blots between appropriate RFLP markers and the CHEF gels. Eleven of the 12 chromosomes are meiotically stable, but the 12th (and smallest) is subject to deletions in 3% (4/121) of the progeny. Positive chiasma interference occurred on five of the 12 chromosomes, and nine of the 12 chromosomes averaged more than one crossover per chromosome. The average kb/cM ratio in this cross is-32.
Kansas and California wheat-growing regions differ dramatically in soils, climate, wheat cultivar... more Kansas and California wheat-growing regions differ dramatically in soils, climate, wheat cultivars, crop rotation patterns, and cultural practices, which could select for different fungal populations of Mycosphaerella graminicola. Our objective in this study was to use amplified fragment length polymorphism (AFLP) loci to assess the genetic diversity of M. graminicola populations within single fields in two widely separated, and geographically isolated sites in Kansas and California. Three primer-pair combinations were used to resolve polymorphism at 177 loci in 67 and 63 isolates from Kansas and California, respectively. Genotypic variability was high, which is consistent with a genetically diverse initial inoculum. There was no evidence of genetic disequilibrium in either population, with only 4.6% of the locus pairs in Kansas, and 5.4% of the locus pairs in California in detectable disequilibrium. The migration rate calculated between the two sites was as low as 1.8 individuals per generation, and significant differences in allele frequencies were observed. Therefore, these two populations do not represent mere subsamples of a larger, randomly mating population. This is a rare report of isolation by distance occurring between two North American populations of M. graminicola, indicating that at least some of these populations may be differentiating. Although genetic isolation by distance may occur, we cannot exclude movement of new gene combinations such as fungicide resistance or virulence between these two locations.
Wild-collected isolates of Neurospora crassa Shear and Dodge were systematically examined for rec... more Wild-collected isolates of Neurospora crassa Shear and Dodge were systematically examined for recessive mutations affecting the sexual phase of the life cycle, which is essentially diploid. Seventy-four of 99 wild-collected isolates from 26 populations in the United States, India and Pakistan carried one or more recessive mutations that reduced fertility significantly when homozygous; mutations affecting spore morphology were also detected. Limited complementation tests indicate that most of the 106 recovered mutations are unique.-T h e recessive diplophase (= sexual phase) mutations were uncovered by crossing each wild-collected isolate to a marked two-chromosome double-reciprocal translocation strain as "balancer." Surviving progeny receive approximately 60% of their genome from the wild parent, but receive the mating-type allele from the "balancer" parent. These progeny were backcrossed to the wild parent and were also crossed with a standard laboratory strain (fl). Reduced fertility in the backcross us. normal fertility in the cross with the laboratory standard signals the presence of a recessive mutation in the wild-collected isolate.-Most of the mutants (95 of 106) fall into two major classes: those producing barren perithecia with no or few viable ascospores (51) and those with spore maturation defects (44). Most of the recessive barrens result either from an early block in meiosis o r ascus development (25) o r from a late disturbance in postmeiotic ascus behavior (1 8).-These recessive mutations are formally equivalent to recessive lethals in higher eukaryotes and may be important in determining the breeding structure of natural Neurospora populations. EUROSPORA crassa Shear and Dodge is genetically and biochemically one of the most intensively studied eukaryotic microbes, but little was known of natural Neurospora populations until systematic collections were begun in 1969 (PERKINS, TURNER and BARRY 1976). Wild-collected Neurospora have since been examined for electrophoretic enzyme polymorphisms (SPIETH 1975), Spore killers (a meiotic drive phenomenon, TURNER and PERKINS 1979), vegetative (heterokaryon) incompatibility (MYLYK 1976), variations in ribosomal DNA organization (RUSSELL et al. 1984), DNA restriction fragment length polymorphisms (METZENBERG et al. 1984) and mitochondrial DNA composition ' To whom correspondence should be addressed.
Genetic maps are useful for researchers outside the originating laboratory only if the strains an... more Genetic maps are useful for researchers outside the originating laboratory only if the strains and markers used in the analysis of the mapping population and the genotypes of the strains composing the mapping population are available for analysis. This brief communication gives the genotypes for the strains that compose a recently constructed mapping population of G. fujikuroi. Strains and probes are available from FGSC.
Frontiers in sustainable food systems, Jan 27, 2023
Mycotoxins, such as aflatoxins, fumonisins, trichothecenes, and zearalenone, are increasing in vi... more Mycotoxins, such as aflatoxins, fumonisins, trichothecenes, and zearalenone, are increasing in visibility as a public health threat through both acute and chronic exposure in food. USAID through its Feed the Future program has sponsored research in Nepal on mycotoxin contamination and the correlated high levels of stunting in children under age five. Communicating about mycotoxins is a complicated matter, as is communicating about any potentially serious economic or health threat that may be di cult to control. Two nominal group workshops in Nepal focused on identifying problems from multiple perspectives and developing potential communication strategies to mitigate the problem and potential concerns about it. Target audiences were identified along with their interests and e ective channels to communicate with and within them. The first audience to work with is the government, as it must understand and value the problem and help generate confidence in potential regulatory and mitigation processes. Producers, educators and health professionals are the next audiences to address as they are the most closely involved with the problem. Consumer engagement is last, with a communication goal of sharing information to heighten awareness and minimize unwarranted public concern.
The polymerase chain reaction (PCR) is a method for amplifying specific segments of DNA defined b... more The polymerase chain reaction (PCR) is a method for amplifying specific segments of DNA defined by the small primers used to start the reaction. Using arbitrarily chosen 10-base primers, one can generate "random amplified polymorphic DNA" (RAPD) markers (Williams et al. 1991 Nucl. Acids Res. 18:6531-6535). These DNA fragments, separated by electrophoresis in an agarose gel, can be used as markers for studying genetic variation within and among fungal populations.
Gibberella fujikuroi and Gibberella intermedia (mating populations 'C' and 'D' of the G. fujikuro... more Gibberella fujikuroi and Gibberella intermedia (mating populations 'C' and 'D' of the G. fujikuroi species complex) can be distinguished by differences in the spectrum of mycotoxins produced, the lack of sexual cross-fertility and diagnostic differences in their DNA sequences. Some isolates from these two biological species, however, can interbreed and complete meiosis to produce viable progeny. Analysis of marker segregation amongst such hybrid progeny can be used to estimate the degree of genomic rearrangement and genetic incompatibility that has accumulated since these sibling species diverged. Recombinant progeny were isolated from crosses of the standard tester strains for these two species and from crosses between these standard testers and a field isolate (KSU X-10626) that was cross-fertile with tester strains of both species. Progeny in all of the crosses segregated for amplified fragment length polymorphisms (AFLPs). Segregation of AFLP loci deviated from 1:1 for two thirds of the loci amongst the progeny of the cross between the 'C' and 'D' mating population tester strains, but <20% of the polymorphic loci in the cross of either tester with KSU X-10626 showed such distortion. It was concluded that G. intermedia and G. fujikuroi are sufficiently interfertile to belong to the same biological species, but that changing the nomenclature to reflect this interfertility requires more evidence for the natural occurrence of a continuum in fertility than is presently available.
Gene conversion causes deviations from the 2:2 segregation of allele pairs in meiosis. Thus, gene... more Gene conversion causes deviations from the 2:2 segregation of allele pairs in meiosis. Thus, gene co'nversion is a potential cause for changes of allele frequencies in populations. Equations are derived for the effects of conversion in a large random-mating population. The influence of gene conversion on allele frequencies is compared with that of spontaneous mutation and meiotic drive.
THIL;VL;IIR;VR) BLNC-1 is a compound chromosome rearrangement in Neurospora crassa that combines ... more THIL;VL;IIR;VR) BLNC-1 is a compound chromosome rearrangement in Neurospora crassa that combines two reciprocal translocations: T(IIL; VL) A R30 which interchb.nges the left end of linkage group II with the left end of linkage group V, and T(IIR;VR) ALSI54 which interchanges the right end of linkage group II with the right end of linkage group V. BLNC-I acts as a crossover suppressor for most of both linkage groups II and V since single crossovers between the rearrangement breakpoints result in progeny with lethal unbalanced duplications and deficiencies. The integrity of BLNC-I following meiosis was tested in crosses of marked BLNC-I by marked Normal sequence, with markers located at critical points on linkage groups I1 and V. Although recombination between distal markers in the four arms was reduced markedly, double crossovers in the long intervening regions occurred with a frequency of 21%. Of these double crossovers, most were coincidental crossovers, one in each of the long intervening regions, resulting in the resolution of the complex into its component rearrangements (16%), while a minority of the double crossovers (5%) were crossovers involving only one of the two component linkage groups, and resulted in the insertion of a segment between the breakpoints.-The BLNC-1 balancer can be used for: (1) mapping new loci to linkage groups II and V, especially for identifying markers mapping near the tips of the linkage groups; (2) for isolating genetically intact chromosomes from natural populations or for quantitative genetic studies; and (3) for studying recombinational hot-spots which can be detected as escapes from crossover suppression.-Based on experience with BLNC-I, future two-chromosome balancers should be designed with two breakpoints near, but not at, the opposite ends of the chromosome to be balanced, and the other two breakpoints close to, but spanning, the centromere of a second chromosome. Such a construction when combined with appropriately placed selective markers should prevent breakdown of the complex, and should resemble an inversion in eliminating crossover products.
It has never been determined in Neurospora whether multiple alleles exist at individual het loci ... more It has never been determined in Neurospora whether multiple alleles exist at individual het loci such that interaction between any two unlike alleles will result in an incompatibility reaction. The evidence summarized here from recombination genetics and from sampling natural populations suggests multiple allelism at two of the best studied het loci. However, an alternate explanation is not excluded that invokes linked multiple loci rather than multiple alleles.
The regulatory gene nit-2 of Neurospora crassa complements a nnu mutant of Gibberella zeae (Fusar... more The regulatory gene nit-2 of Neurospora crassa complements a nnu mutant of Gibberella zeae (Fusarium graminearum
Chromosome rearrangements between fungal strains may reduce fertility in sexual crosses through t... more Chromosome rearrangements between fungal strains may reduce fertility in sexual crosses through the production of genetically inviable recombinant progeny. As such, rearrangements can be important postzygotic reproductive barriers that contribute to the speciation process. The presence of chromosome rearrangements in crosses with Gibberella zeae was tested by counting asci with 8, 6, 4, or 2 viable ascospores. Counts were made by observing rosettes of asci extruded from crushed perithecia and by observing unordered ascospore tetrads ejected onto agar slabs from mature perithecia. The two methods gave similar results. Self-fertilized cultures served as controls and produced the normal eight ascospores per ascus in >98% of cases. Crosses with strains known to carry chromosome rearrangements produced significant frequencies of asci with 6, 4, or 2 ascospores, as expected. These results suggest that these methods will be useful to survey populations of G. zeae for chromosome rearrangements.
Canadian journal of genetics and cytology, Dec 1, 1982
In ln(IL; IR)OY323 of Neurospora crassa, a long central segment of linkage group I is inverted th... more In ln(IL; IR)OY323 of Neurospora crassa, a long central segment of linkage group I is inverted that includes the centromere. This is the first interstitial pericentric inversion to be identified in a fungus. In genetic and cytological behavior, it resembles chromosome inversions in higher eukaryotes. In crosses heterozygous for the OY323 inversion, normally distant markers are closely linked, while in homozygous inversion crosses the gene order is reversed, but recombination is approximately normal within the inverted segment. A characteristic inversion loop may form at pachytene in heterozygous crosses; frequently, segments distal to the breakpoints do not pair, however. Rearrangement breakpoints were mapped precisely by duplication coverage using appropriate recessive markers in crosses of OY323 with a partially overlapping inversion, In(IL→IR)NM176.
The initiation of monokaryotic fruiting in the basidiomycetous fungus Schizophyllum commune has b... more The initiation of monokaryotic fruiting in the basidiomycetous fungus Schizophyllum commune has been observed to occur spontaneously, in response to biochemical substances, and following mechanical injury. The responses to these three stimuli are genetically separable and under polygenic control.
Fusarium subglutinans and F. temperatum are two important fungal pathogens of maize whose distinc... more Fusarium subglutinans and F. temperatum are two important fungal pathogens of maize whose distinctness as separate species has been difficult to assess. We isolated strains of these species from commercial and native maize varieties in Argentina and sequenced >28,000 loci to estimate genetic variation in the sample. Our objectives were to measure genetic divergence between the species, infer demographic parameters related to their split, and describe the population structure of the sample. When analyzed together, over 30% of each species’ polymorphic sites (>2,500 sites) segregate as polymorphisms in the other. Demographic modeling confirmed the species split predated maize domestication, but subsequent between-species gene flow has occurred, with gene flow from F. subglutinans into F. temperatum greater than gene flow in the reverse direction. In F. subglutinans, little evidence exists for substructure or recent selective sweeps, but there is evidence for limited sexual repro...
Members of the fungal genus Fusarium can produce numerous secondary metabolites, including the no... more Members of the fungal genus Fusarium can produce numerous secondary metabolites, including the nonribosomal mycotoxins beauvericin (BEA) and enniatins (ENNs). Both mycotoxins are synthesized by the multifunctional enzyme enniatin synthetase (ESYN1) that contains both peptide synthetase and S-adenosyl-l-methionine-dependent N-methyltransferase activities. Several Fusarium species can produce ENNs, BEA or both, but the mechanism(s) enabling these differential metabolic profiles is unknown. In this study, we analyzed the primary structure of ESYN1 by sequencing esyn1 transcripts from different Fusarium species. We measured ENNs and BEA production by ultra-performance liquid chromatography coupled with photodiode array and Acquity QDa mass detector (UPLC-PDA-QDa) analyses. We predicted protein structures, compared the predictions by multivariate analysis methods and found a striking correlation between BEA/ENN-producing profiles and ESYN1 three-dimensional structures. Structural differe...
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Papers by John Leslie