α-mating-type-specific suppression and a-mating-type-specific enhancement by tunicamycin of sexual agglutinability in the yeast Saccharomyces cervisiae

Effects of tunicamycin (TM) on the sexual agglutinability and zygote formation of Saccharomyces cerevisiae were studied using the two kinds of haploid strains, inducible and constitutive for sexual agglutinability. Induction of sexual agglutinability by opposite mating type sex pheromone of inducible strains was inhibited by TM in mating type but not in a mating type. The recovery by temperature-shift-down from the temperature-suppressed sexual agglutinability of constitutive strains was enhanced by TM in a mating type but rather inhibited in mating type. Pretreatment with TM of constitutive strains enhanced sexual agglutinability in a mating type but not in mating type. The above-mentioned a-mating-type-specific agglutinability-enhancing actions of TM were discussed in relation to the action mechanism of pheromone which induces or enhances the sexual agglutinability of a cells.Zygote formation was inhibited by TM in both constitutive and inducible strains at concentrations which showed only partially inhibitory effect on sexual agglutinability.Abbreviations AI agglutination index - TM tunicamycin     

Cell Fusion Promoting Factor Common to Homothallic and Heterothallic Mating Systems in Dictyostelium discoideum1

Cellular slime mould Dictyostelium discoideum propagates as single haploid cells and under certain environmental conditions enters into a sexual cycle called macrocyst formation. There are homothallic and heterothallic strains reported, the former being able to form macrocysts in clonal cell populations while the latter to do so only in the presence of opposite mating-type strains. Molecular basis for differential mating systems is an intersting subject totally unknown yet. In the present study, sexual cell interactions in AC4, a homothallic strain of D. discoideum, was studied in comparison with the heterothallic mating system. The conditoned medium of AC4 cells was found to promote the sexual cell fusion among themselves. In addition, it also enhanced the cell fusion between heterothallic strains. Furthermore, the conditioned medium obtained from the mated culture of heterothallic strains reported to induce the sexual cell fusion in the heterothallic strains (Saga and Yanagisawa, 1983) was found also to promote the cell fusion in AC4. These results suggest that common regulatory mechanisms operate for sexual cell fusion among different mating systems in D. discoideum.     

Dynamic linkage relationships to the mating‐type locus in automictic fungi of the genus Microbotryum

Regions of the chromosomes determining mating compatibility in some fungi, including Microbotryum lychnidis‐dioicae and Neurospora tetrasperma, exhibit suppressed recombination similar to sex chromosomes in plants and animals, and recent studies have sought to apply basic theories of sex chromosome evolution to fungi. A phylogeny of the MTL1 locus in Microbotryum indicates that it has become part of the nonrecombining regions of the mating‐type chromosomes in multiple independent events, and that recombination may have been subsequently restored in some cases. This illustrates that fungal mating‐type chromosomes can exhibit linkage relationship that are quite dynamic, adding to the list of similarities to animal or plant sex chromosomes. However, fungi such as M. lychnidis‐dioicae and N. tetrasperma exhibit an automictic mating system, for which an alternate theoretical framework exists to explain the evolution of linkage with the mating‐type locus. This study encourages further comparative studies among fungi to evaluate the role of mating systems in determining the evolution of fungal mating‐type chromosomes.     

桦纤孔菌有性生殖相关特征及交配型位点分析

对桦纤孔菌菌株MDJCBS88的显微形态、菌丝及担孢子核相进行了观察。采用棉籽壳培养基对担孢子萌发形成的菌株进行栽培试验,筛选出不形成子实体或子实体发育不完整的菌株,将这些菌株在平板上进行了亲和试验,分析桦纤孔菌的有性生殖方式;并基于基因组序列进行交配型基因克隆验证,分析桦纤孔菌的交配型位点结构。显微观察发现,桦纤孔菌菌丝没有锁状联合结构,菌丝细胞无核到多核;子实层担孢子可含0-4个不等的细胞核,不同时期弹射的担孢子含有的细胞核数量不同。桦纤孔菌担孢子萌发率极低,能萌发的担孢子多为早期弹射的担孢子;培养基也影响担孢子的萌发率,与PDA培养基和CYM培养基相比,桦木屑培养基最适合桦纤孔菌担孢子萌发,萌发率为4.55%。从担孢子萌发的96个菌株中获得了2个不结实菌株和9个结实不产孢菌株,占11.5%,这些菌株间亲和试验出现不同的表现特征,包括形成产孢子实体,产生菌丝纽结,相互融合和相互拮抗等现象,认为桦纤孔菌的有性生殖以次级同宗结合为主,并受交配型基因控制。交配型位点克隆测序后分析发现,桦纤孔菌交配型A位点共14 034 bp,含有一个MIP基因和两组HD1和HD2基因;交配型B位点包含3个疑似信息素受体基因和1个信息素前体编码基因。     

LINKAGE TO THE MATING‐TYPE LOCUS ACROSS THE GENUS MICROBOTRYUM: INSIGHTS INTO NONRECOMBINING CHROMOSOMES

Parallels have been drawn between the evolution of nonrecombining regions in fungal mating‐type chromosomes and animal and plant sex chromosomes, particularly regarding the stages of recombination cessation forming evolutionary strata of allelic divergence. Currently, evidence and explanations for recombination cessation in fungi are sparse, and the presence of evolutionary strata has been examined in a minimal number of fungal taxa. Here, the basidiomycete genus Microbotryum was used to determine the history of recombination cessation for loci on the mating‐type chromosomes. Ancestry of linkage with mating type for 13 loci was assessed across 20 species by a phylogenetic method. No locus was found to exhibit trans‐specific polymorphism for alternate alleles as old as the mating pheromone receptor, indicating that ages of linkage to mating type varied among the loci. The ordering of loci in the ancestry of linkage to mating type does not agree with their previously proposed assignments to evolutionary strata. This study suggests that processes capable of influencing divergence between alternate alleles may act at loci in the nonrecombining regions (e.g., gene conversion) and encourages further work to dissect the evolutionary processes acting upon genomic regions that determine mating compatibility.     

Hybridization and sexual stimulation inTrichophyton mentagrophytes

Mating and sexual stimulation tests applied to 132 strains of this dermatophyte isolated in Czechoslovakia revealed among them strains ofArthroderma benhamiae (40 strains of the+mating type, one of the—mating type) andA. vanbreuseghemii (three strains of the+type, seven of the-type). No dependence was found concerning the anamorphic variety (T. mentagrophytes var.granulosum, var.interdigitale, var.mentagrophytes, var.quinckeanum), teleomorphic species, mating type and the clinical localization of dermatophytosis. Plausible reasons of different frequencies of the mating types are discussed.     

Breaking linkage between mating compatibility factors: Tetrapolarity in Microbotryum

Linkage of genes determining separate self‐incompatibility mechanisms is a general expectation of sexual eukaryotes that helps to resolve conflicts between reproductive assurance and recombination. However, in some organisms, multiple loci are required to be heterozygous in offspring while segregating independently in meiosis. This condition, termed “tetrapolarity” in basidiomycete fungi, originated in the ancestor to that phylum, and there have been multiple reports of subsequent transitions to “bipolarity” (i.e., linkage of separate mating factors). In the genus Microbotryum, we present the first report of the breaking of linkage between two haploid self‐incompatibility factors and derivation of a tetrapolar breeding system. This breaking of linkage is associated with major alteration of genome structure, with the compatibility factors residing on separate mating‐type chromosome pairs, reduced in size but retaining the structural dimorphism characteristic for regions of recombination suppression. The challenge to reproductive assurance from unlinked compatibility factors may be overcome by the automictic mating system in Microbotryum (i.e., mating among products of the same meiosis). As a curious outcome, this linkage transition and its effects upon outcrossing compatibility rates may reinforce automixis as a mating system. These observations contribute to understanding mating systems and linkage as fundamental principles of sexual life cycles, with potential impacts on conventional wisdom regarding mating‐type evolution.     

我国肺形侧耳栽培菌株交配型分析

为分析我国栽培肺形侧耳的遗传多样性,对肺形侧耳菌株的交配型进行测定,测试的肺形侧耳菌株包括俗称为秀珍菇和凤尾菇的菌株。结果显示,我国栽培的秀珍菇与凤尾菇菌株间可以发生性亲和,属于同一生物学物种,但它们之间的交配型特异性低,36个菌株中只含4种A交配型和3种B交配型,暗示我国栽培的肺形侧耳种质资源基因匮乏。     

Sexual reproduction and recombination in the aflatoxin-producing fungus Aspergillus parasiticus

The fungal phylum Ascomycota comprises a large proportion of species with no known sexual stage, despite high genetic variability in field populations. One such asexual species, Aspergillus parasiticus, is a potent producer of carcinogenic and hepatotoxic aflatoxins, polyketide-derived secondary metabolites that contaminate a wide variety of agricultural crops. In this study, individuals of A. parasiticus from a population showing an evolutionary history of recombination were examined for sexual reproduction. Crosses between strains with opposite mating-type genes MAT1-1 and MAT1-2 resulted in the development of ascospore-bearing ascocarps embedded within stromata. Sexually compatible strains belonged to different vegetative compatibility groups. Recombination through the independent assortment of chromosomes 3 and 6 was detected using loci for mating type, aflatoxin gene cluster, and a protein-encoding gene. Our discovery of the sexual stage in A. parasiticus has important implications for current biological control strategies using nontoxigenic strains to reduce aflatoxin contamination in crops.     

A MAT1–2 wild‐type strain from Penicillium chrysogenum: functional mating‐type locus characterization,genome sequencing and mating with an industrial penicillin‐producing strain

In heterothallic ascomycetes, mating is controlled by two nonallelic idiomorphs that determine the ‘sex’ of the corresponding strains. We recently discovered mating‐type loci and a sexual life cycle in the penicillin‐producing fungus, Penicillium chrysogenum. All industrial penicillin production strains worldwide are derived from a MAT1‐1 isolate. No MAT1‐2 strain has been investigated in detail until now. Here, we provide the first functional analysis of a MAT1‐2 locus from a wild‐type strain. Similar to MAT1‐1, the MAT1‐2 locus has functions beyond sexual development. Unlike MAT1‐1, the MAT1‐2 locus affects germination and surface properties of conidiospores and controls light‐dependent asexual sporulation. Mating of the MAT1‐2 wild type with a MAT1‐1 high penicillin producer generated sexual spores. We determined the genomic sequences of parental and progeny strains using next‐generation sequencing and found evidence for genome‐wide recombination. SNP calling showed that derived industrial strains had an uneven distribution of point mutations compared with the wild type. We found evidence for meiotic recombination in all chromosomes. Our results point to a strategy combining the use of mating‐type genes, genetics, and next‐generation sequencing to optimize conventional strain improvement methods.     

Isolation of plasmids carrying the arginine repressor gene argR of Escherichia coli K12

Summary Twenty-two sexual crosses between strains of Phycomyces blakesleeanus carrying mutations affecting phototropism (madA, madD, madE), synthesis of carotenoids (carA), auxotrophy (leu-51, nicA, pur-51), and resistance to 5-fluorouracil (fur) were studied; mating type was also included as a marker. Recombination frequencies were obtained among the ten genes involved. Linkage was found between mating type and madE; leu-51 and madA; furA401, furB402 and madD. All other gene combinations tested are unliked.     

Variation in mating propensity and fertility in isofemale strains of Drosophila ananassae

Mating propensity and fertility were studied in five laboratory strains of Drosophila ananassae which were established from single females collected from different geographical localities. The results show statistically significant variation among different isofemale lines with respect to mating propensity and fertility. The strains showing greater sexual activity produce more progeny. Thus, there is a positive correlation between mating activity and fertility in D. ananassae. The comparison of mating frequencies of strains and their hybrids reveals the existence of heterosis and reciprocal effects. The data suggest that the males are more subject to intrasexual selection.     

Genetic isolation among sympatric vegetative compatibility groups of the aflatoxin‐producing fungus Aspergillus flavus

Aspergillus flavus, a fungal pathogen of animals and both wild and economically important plants, is most recognized for producing aflatoxin, a cancer‐causing secondary metabolite that contaminates food and animal feed globally. Aspergillus flavus has two self/nonself recognition systems, a sexual compatibility system and a vegetative incompatibility system, and both play a role in directing gene flow in populations. Aspergillus flavus reproduces clonally in wild and agricultural settings, but whether a cryptic sexual stage exists in nature is currently unknown. We investigated the distribution of genetic variation in 243 samples collected over 4 years from three common vegetative compatibility groups (VCGs) in Arizona and Texas from cotton using 24 microsatellite loci and the mating type locus (MAT) to assess population structure and potential gene flow among A. flavus VCGs in sympatric populations. All isolates within a VCG had the same mating type with OD02 having MAT1‐2 and both CG136 and MR17 having MAT1‐1. Our results support the hypothesis that these three A. flavus VCGs are genetically isolated. We found high levels of genetic differentiation and no evidence of gene flow between VCGs, including VCGs of opposite mating‐type. Our results suggest that these VCGs diverged before domestication of agricultural hosts (>10 000 yr bp ).     

<Emphasis Type="Italic">Sporidiobolus johnsonii</Emphasis> and <Emphasis Type="Italic">Sporidiobolus salmonicolor</Emphasis> revisited

The relationship between Sporidiobolus johnsonii and S. salmonicolor was investigated using rDNA sequence data. Two statistically well-supported clades were obtained. One clade included the type strain of S. johnsonii and the other included the type strain of S. salmonicolor. However, some mating strains of S. salmonicolor were found in the S. johnsonii group. These strains belonged to mating type A2 and were sexually compatible with mating type A1 strains from the S. salmonicolor group. DNA–DNA reassociation values were high within each clade and moderate between the two clades. In the re-investigation of teliospore germination, we observed that the basidia of S. salmonicolor were two-celled. In S. johnsonii, basidia were not formed and teliospore germination resulted in direct formation of yeast cells. We hypothesize that the S. johnsonii clade is becoming genetically isolated from the S. salmonicolor group and that a speciation process is presently going on. We suspect that the observed sexual compatibility between strains of the S. johnsonii and S. salmonicolor groups and the possible genetic flow between the two species has little biological relevance because distinct phenotypes have been fixed in the two taxa and intermediate (hybrid) sequences for LSU and ITS rDNAs have not been detected. An erratum to this article can be found at     

Gibberella fujikuroi mating population E is associated with maize and teosinte

Isolates of Fusarium subglutinans mating population E are usually found on maize. This fungus forms part of the so-called Gibberella fujikuroi species complex. Previously, F. subglutinans has been associated with two additional mating populations (B and H) and a variety of plant hosts. This was mainly due to a lack of diagnostic morphological characters, but the use of DNA sequence information showed that the strains making up mating populations B, E and H, as well as those associated with the different plant hosts, represent separate species. Recently, another putative mating population has been reported on the wild teosinte relatives of maize. Based on sexual compatibility studies, these isolates were apparently closely related to the pitch canker fungus, F. subglutinans f. sp. pini (= F. circinatum;G. fujikuroi mating population H). The aim of the current study was to determine whether the population of F. subglutinans from teosinte constitutes a new or an existing lineage within the G. fujikuroi complex. For this purpose, portions of the mitochondrial small subunit ribosomal DNA, calmodulin and β-tubulin genes from the fungi were sequenced. Phylogenetic analyses and comparison with sequences from public domain databases indicated that the F. subglutinans isolates from teosinte are most closely related to strains of G. fujikuroi mating population E. These results were confirmed using sexual compatibility studies. The putative mating population from the wild relatives of maize therefore forms part of the existing E-mating population and does not constitute a new lineage in the G. fujikuroi species complex.     

Inheritance Features of Mating Behavior Components in <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> and Their Significance for Fitness

Components of mating behavior of Drosophila melanogaster mutant and wild-type strains were studied with respect to fitness. The magnitude of the effect of genotype on the male mating activity, female sexual receptivity, fertility and viability was determined. Strong positive correlation was found between the male mating activity and fitness components. It was shown that mating of strains contrasting in sexual behavior features can be accompanied by both heterosis and maternal effect. Inheritance coefficients were determined for sexual behavior components.__________Translated from Genetika, Vol. 41, No. 5, 2005, pp. 614–619.Original Russian Text Copyright © 2005 by Volkova, Vorobjova.     

A STUDY OF THE SEXUAL REPRODUCTION AND DETERMINATION OF MATING TYPE OF GYMNODINIUM NOLLERI (DINOPHYCEAE) IN CULTURE1

Sexual reproduction of Gymnodinium nolleri ( Ellegaard & Moestrup 1999 ) was studied by intercrossing experiments in all combinations of six clonal strains and backcrossing of five clonal F1 offspring. The results indicated that the conjugation of G. nolleri responded to the existence of more than two sexual types (complex heterothallism) and that compatibility between progeny of one cyst (inbreeding) was the rule. Sexual fusion, planozygote formation and development, cyst formation, and germination and planomeiocyte division were followed using time‐lapse photography. This study revealed many similarities between the sexual stages and life cycle pattern of G. nolleri and the related G. catenatum and the existence under culture conditions of an alternative cycle between vegetative cells and zygotes without a hypnozygote stage. The fate of zygotes, division or encystment, was influenced by the nutritional status of the external medium. The division of G. nolleri planozygotes was promoted by high levels of external nutrients, whereas the maximum percentage of encystment was recorded when phosphates were reduced in the isolation medium. The division of zygotes might be different from both vegetative and planomeiocyte division because it resulted in two‐cell chains with the cells not oriented in parallel.     

Sexual selection in fungi

The significance of sexual selection, the component of natural selection associated with variation in mating success, is well established for the evolution of animals and plants, but not for the evolution of fungi. Even though fungi do not have separate sexes, most filamentous fungi mate in a hermaphroditic fashion, with distinct sex roles, that is, investment in large gametes (female role) and fertilization by other small gametes (male role). Fungi compete to fertilize, analogous to ‘male‐male’ competition, whereas they can be selective when being fertilized, analogous to female choice. Mating types, which determine genetic compatibility among fungal gametes, are important for sexual selection in two respects. First, genes at the mating‐type loci regulate different aspects of mating and thus can be subject to sexual selection. Second, for sexual selection, not only the two sexes (or sex roles) but also the mating types can form the classes, the members of which compete for access to members of the other class. This is significant if mating‐type gene products are costly, thus signalling genetic quality according to Zahavi's handicap principle. We propose that sexual selection explains various fungal characteristics such as the observed high redundancy of pheromones at the B mating‐type locus of Agaricomycotina, the occurrence of multiple types of spores in Ascomycotina or the strong pheromone signalling in yeasts. Furthermore, we argue that fungi are good model systems to experimentally study fundamental aspects of sexual selection, due to their fast generation times and high diversity of life cycles and mating systems.     

Mating system and DNA polymorphism of monokaryons with different mating type of Stropharia rugoso-annulata

The mating system of Stropharia rugoso-annulata Farlow apud Murrill was studied by pairing single spore isolates from the same fruitbody, and the genetic diversity of monokaryotic strains with different mating types was evaluated by the RAPD technique. Basidiospores could germinate normally on PGP (potato/glucose/peptone) medium at 30 °C. Analysis of self- and cross-pairings revealed that Stropharia rugoso-annulata was heterothallic and tetrapolar. RAPD analysis detected polymorphism among monokaryotic strains, with more genetic variation within monokaryotic strains with non-parental mating type compared to monokaryotic strains with parental mating type. These results were in general agreement with the existing knowledge, confirming the validity and usefulness of the RAPD technique. Therefore, the RAPD technique will provide an exciting and valuable tool for a large-scale study on identification and genetic resources of monokaryotic strains, and should lead to a more efficient understanding and utilization of genetic diversity of monokaryotic strains in cross breeding by breeders.