Mating Compatibility Research Articles

Bottleneck‐induced dissolution of self‐incompatibility and breeding system consequences in Aster furcatus (Asteraceae)

Aster furcatus is a rare species with extremely limited genetic variation at isozyme loci. We utilized crossing experiments and seed set data obtained from natural populations to verify that there is also little allelic variation at the self‐incompatibility (S) locus. Seed set in several populations was limited by a low number of S‐alleles. Associated with a low number of S‐alleles in populations was the dissolution of the incompatibility system, manifest by individual variation in self‐compatibility, and by complex dominance relationships among S‐alleles. Plant self‐compatibility was correlated with mean number of ovules per inflorescence. Thus, self‐compatibility appeared to be under partial environmental influence. Computer simulations revealed that the shapes of seed set distribution curves of modeled self‐incompatible plant populations depend on the number of incompatibility alleles in the populations. By varying the number of S‐alleles in modeled populations, we generated seed set distribution curves similar to those of natural populations. Genetic bottlenecks reduce the number of S‐alleles and the proportion of compatible matings in populations of multiallelic self‐incompatible species. Self‐compatible genotypes are at a selective advantage in populations that lack a sufficient number of S‐alleles to produce compatible crosses. Aster furcatus appears to be evolving self‐compatibility as a result of bottleneck‐induced losses of S‐alleles.

The Mating System of Melanotus textilis

Melanotus textilis (Strophariaceae), a small saprobic agaric, exhibits a bifactorial (tetrapolar) mating system based on the formation of clamp connections. The mating system is the same as that of M. defraudatus but differs from that of M. hartiae, which is unifactorial (bipolar). Matings from different populations of M. textilis show that the locus controlling mating compatibility is multiallelic. Asexual reproduction by arthroconidia was also observed.

The mating system of Melanotus textilis

Melanotus textilis (Strophariaceae), a small saprobic agaric, exhibits a bifactorial (tetrapolar) mat? ing system based on the formation of clamp connec? tions. The mating system is the same as that of M. defraudatus but differs from that of M. hartiae, which is unifactorial (bipolar). Matings from different pop? ulations of M. textilis show that the locus controlling mating compatibility is multiallelic. Asexual repro? duction by arthroconidia was also observed.

Biogeography of toxic dinoflagellates in the genusAlexandrium from the northeastern United States and Canada

Twenty-eight strains of toxic dinoflagellates in the genusAlexandrium from the northeastern United States and Canada were characterized on the basis of morphology, bioluminescence capacity, mating compatibility, and toxin composition. The distributions of these characters were evaluated in the context of regional patterns of paralytic shellfish poisoning (PSP) and coastal hydrography. Two morphospecies were identified-A. tamarense Lebour andA. fundyense Balech. The two are interspersed geographically though there are areas, such as the Gulf of Maine, where apparently onlyA. fundyense occurs. Southern waters (Cape Cod, Connecticut, and Long Island) have especially diverse populations. The two species are sexually compatible. Virtually all northern isolates are bioluminescent, whereas southern isolates include bioluminescent and non-bioluminescent strains. Cluster analyses, based on high performance liquid chromatography (HPLC) determinations of the suite of toxins produced by each isolate, revealed two and perhaps three distinct groups. One is comprised almost exclusively of northern strains, and the other of southern strains. A Cape Cod cluster may be separable from the southern group. These analyses explain a previously reported north-to-south trend of decreasing toxicity, as the northern isolates produce greater proportions of the more potent toxins than do southern forms. The overall perspective is that the biogeography of toxicAlexandrium spp. in the study region is not that of a single, widespread, homogeneous population, but rather is comprised of several sub-populations, each with its own physiological characteristics and history. Two scenarios are considered with respect to this regional biogeography. The first invokes recent and continuing dispersal of isolates to the south from a center of origin in the north, followed by recombination and strong selection. The second holds that the northern and southern populations diverged from a common ancestor (vicariance), but now represent localized populations with little mixing of genotypes. Neither hypothesis can be completely refuted by the data presented here, though the weight of the evidence favors the latter. The correct scenario may be a combination of both, with recent and continuous speading occuring within the Gulf of Maine and perphaps the Gulf of St. Laerence, but with endemic localized populations persisting without genetic exchange in most southern locations. These data also indicate that although morphological criteria separate toxicAlexandrim isolates from the study region into two morphospecies, these assignments do not coincide with clusterings based on toxin composition or allozyme electrophoresis, and they are further violated by mating results. A revision of taxon designations to the varietal level could be justified.

Pairing tests to determine mating compatibility in Phellinus weirii

Pairings of single-spore (Douglas-fir and western redcedar) isolates of Phellinus weirii from the same basidiocarp produce a wide variety of reactions, from formation of darkly pigmented barrage lines to no visible change in morphology. In contrast, pairings of single-spore isolates from different basidiocarps result in little or no line formation while heterokaryon-homokaryon (vegetative × single-spore isolate) pairings result in strong barrage line formation. Mating compatibility of any single-spore isolates may thus be determined by pairing the isolates, then back-pairing the interacted mycelium with a homokaryon from a different basidiocarp. If the initial pairing was compatible, a strong barrage line appears in the back-pairing. If the initial pairing was incompatible, no line appears. Using this method, it was determined that the genetic system governing mating compatibility in P. weirii is bipolar (governed by a single gene locus) and multiallelic.

Localization of the Mating Type Gene in Agaricus bisporus

The cultivated mushroom Agaricus bisporus is secondarily homothallic. Most basidia produce two basidiospores, each of which receives two of the four postmeiotic nuclei. Usually, the two packaged nuclei carry compatible mating types. Previous studies suggested that there may be only a single mating type locus in A. bisporus. In this study, we determined whether the mating type segregated as a single Mendelian determinant in a cross marked with 64 segregating molecular markers. To score mating types, each of the 52 homokaryotic offspring from this cross was paired with each of the two progenitor homokaryons. Compatible matings were identified by the formation of genetically stable heterokaryons which were verified by assay of restriction fragment length polymorphisms (RFLPs). Data for screening mycelial interactions on petri plates as well as fruit body formation were compared with the RFLP results. Mating types of 43 of the 52 homokaryotic offspring were determined on the basis of RFLP analysis. Our results indicate (i) there is a segregating mating type gene in A. bisporus, (ii) this mating type gene is on the largest linkage group (chromosome I), (iii) mycelial interactions on petri plates were associated with heterokaryon formation under selected conditions, (iv) fruit body formation was dependent upon the mating type gene, and (v) compatible mating types may not always be sufficient for fruiting.

Relationship of Breeding System to Rarity in the Lakeside Daisy (Hymenoxys acaulis var. glabra)

The breeding system of a rare Great Lakes endemic, the lakeside daisy (Hymenoxys acaulis var. glabra), was investigated when plants from a remnant Illinois population produced no seeds for over 15 years. To determine if the Lakeside daisy was self‐incompatible, 20 plants from two populations, Illinois and Ohio, were selfed and outcrossed. Seed/ovule ratios were compared among the different treatments and the location of the incompatibility reaction was identified. Lakeside daisy was found to be self‐incompatible (sporophytic). The last Illinois population was effectively extinct because the remaining plants belonged to the same mating type (Ne = 1) and only produced seeds when outcrossed to the Ohio plants. Cross‐incompatibility was also observed among Ohio plants, suggesting that within large populations, compatible mating types may be rare locally. In addition, inbreeding depression (lower seed/ovule ratios in inbred than in outcrosses) was observed after one generation of inbreeding. Small populations of self‐incompatible species are vulnerable to extinction if the number of self‐incompatibility alleles, either as a result of a bottleneck or of genetic drift, falls below tbe number needed for the breeding system to function. Recovery protocols based on these genetic considerations were developed and implemented in 1988 when Lakeside daisy populations were established at three Illinois nature preserves.

The origin of multiple mating types in mushrooms

Having multiple mating types greatly improves the chances of meeting a compatible mating partner, particularly in an organism like the mushroom that has no sexual differentiation and no mechanism for signalling to a likely mate. Having several thousands of mating types, as some mushrooms do, is, however, remarkable - and even more remarkable is the fact that individuals only recognise that they have met a compatible mate after their cells have fused. How are such large numbers of mating types generated and what is the nature of the intracellular interaction that distinguishes self from non- self? Answers to these fascinating questions come from cloning some of the mating type genes of the ink cap mushroom Coprinus cinereus. A successful mating in Coprinus triggers a major switch in cell type, the conversion of a sterile mycelium with uninucleate cells (monokaryon) to a fertile mycelium with binucleate cells (dikaryon) which differentiates the characteristic fruit bodies. The mating type genes that regulate this developmental switch map to two multiallelic loci designated A and B and these must both carry different alleles for full mating compatibility. A and B independently regulate different steps in the developmental switch, making it possible to study just one component of the system and work in our laboratory has concentrated on understanding the structure and function of the A genes. It is estimated that some 160 different A mating types exist in nature, any two of which can together trigger the A-regulated part of sexual development. The first clue to how such large numbers are generated came from classical genetic analysis, which identified two functionally redundant A loci, (alpha) and beta. Functional redundancy is, indeed, the key to multiple A mating types and, as seen in Fig.1, molecular cloning has identified many more genes than was possible by recombination analysis.

Intersterility groups in the Pleurotus ostreatus complex from the continental United States and adjacent Canada

Mating compatibility studies using strains from 170 North American collections in the Pleurotus ostreatus complex reveal three intersterile species of oyster mushrooms in the United States and Canada. Initial pairings among monokaryotic single spore isolates were performed to determine the number of intersterile groups. Dikaryon – monokaryon pairings using monokaryotic tester strains were then used to screen additional dikaryotic cultures of the oyster mushroom. Pairings of tester strains from Europe indicate that two European taxa, P. ostreatus and Pleurotus pulmonarius, are also widely distributed in North America. A third intersterility group occurring primarily on aspen in North America was intersterile with all other known species, and is described as a new species, Pleurotus populinus. All three species differ from one another in their morphology, growth characteristics, geographic distributions, and host ranges. Other than mating compatibility tests, however, no single type of character was found to be completely reliable for distinguishing these species in the field or under laboratory conditions. Furthermore, morphological characters used to distinguish European species of the P. ostreatus complex were not useful when applied to corresponding mating-compatible groups from North America. Key words: oyster mushroom, species concept, mating incompatibility.

Re-examination of Psilocybe subaeruginosa and related species with comparative morphology, isozymes and mating compatibility studies

Comparative morphology, isozyme analysis and mating compatibility approaches were used to investigate the relationships between Psilocybe subaeruginosa and three closely related taxa, P. australiana, P. eucalypta and P. tasmaniana . The four names were found to represent one species, and the use of microscopic features such as coloured pleurocystidia or neck length of cheilocystidia were shown to be inappropriate taxonomic discriminators in the separation of the four taxa. Zymograms of extracellular enzymes of laccase, peroxidase, acid phosphatase, pectinesterase and polygalacturonase were useful tools for delineation of taxa within the genus Psilocybe . The name P. subaeruginosa is retained and P. australiana, P. eucalypta and P. tasmaniana are reduced to synonyms. A lectotype is designated. Investigation of isozyme bands previously reported to be pectinlyase activities showed that they were non-enzymic in nature, and interpretation of these pectinlyase activities should be approached with caution.

Clamp Connections in North American Armillaria Species: Occurrence and Potential Application for Delimiting Species

Clamp connections were observed in basidiospore dilutions from each of four North American biological species of Armillaria (A. gallica, A. sinapina, A. ostoyae, and A. calvescens) following spore germination and hyphal anastomosis. The occurrence of clamp connections in intrabasidioma pairings of single-germinated basidiospores and of excised margin-hyphae of Armillaria ostoyae and A. gallica was that expected of a bifactorial incompatibility system. All intraspecific pairings between basidiospores or excised margin-hyphae from actively growing haploid cultures from two different basidiomata of A. ostoyae and of A. gallica produced clamp connections. The development of the crustose colony morphology was almost fully coincident with the formation of clamp connections in compatible matings with either A. ostoyae or A. gallica. Results indicate that clamp connections occur predictably and provide an additional precise and useful criterion for recognizing biological species of Armillaria. For unexplained reasons, haploid isolates paired more than 3 mm apart failed to produce clamp connections.

Clamp Connections in North American Armillaria Species: Occurrence and Potential Application for Delimiting Species

Clamp connections were observed in basidiospore dilutions from each of four North American biological species of Armillaria (A. gallica, A. sinapina, A. ostoyae, and A. calvescens) following spore germination and hyphal anastomosis. The occurrence of clamp connections in intrabasidioma pairings of single-germinated basidiospores and of excised margin-hyphae of Armillaria ostoyae and A. gallica was that expected of a bifactorial incompatibility system. All intraspecific pairings between basidiospores or excised margin-hyphae from actively growing haploid cultures from two different basidiomata of A. ostoyae and of A. gallica produced clamp connections. The development of the crustose colony morphology was almost fully coincident with the formation of clamp connections in compatible matings with either A. ostoyae or A. gallica. Results indicate that clamp connections occur predictably and provide an additional precise and useful criterion for recognizing biological species of Armillaria. For unexplained reasons, haploid isolates paired more than 3 mm apart failed to produce clamp connections.

Sexual Development of Cellular Slime Molds: (cellular slime molds/sexual development/cell interactions/sex pheromones/asexual mutants).

Macrocyst formation represents sexual development of cellular slime molds and begins with fusion between cells of compatible mating types. Homothallic and heterothallic strains as well as bisexual and asexual ones have been described. Macrocyst development requires certain environmental conditions such as darkness and excessive humidity. Sexual cell fusion has been analyzed at a molecular level in Dictyostelium discoideum, and several cell surface proteins related to it have been identified. Some of them are common to both mating types, while others are specific to one or other type. The involvement of cell-surface carbohydrates has also been suggested, though direct evidence for this is still lacking. Macrocyst formation is regulated by diffusible, pheromone like substances. Genetic studies on sexual development are scarce, probably because no suitable mutants have been available. However, several asexual mutants, as well as antibody and nucleotide probes, have recently been obtained, so mechanisms of sexual cell fusion may be understood in the near future. Considering the unique phylogenical position of cellular slime molds, analysis of sexual development in these organisms should contribute to the understanding of the mechanism and evolution of sexual reproduction systems.

Molecular and functional analysis of the A mating type genes of Coprinus cinereus.

The mushroom Coprinus cinereus has a typical hymenomycete life cycle (1). Two different vegetative states can be distinguished, the self sterile monokaryon and the fertile dikaryon. The monokaryon is the mycelium which develops from a single sexual spore. It has uninucleate cells and produces abundant asexual spores, the oidia. The dikaryon is formed by a compatible mating between two monokaryons. It has binucleate cells, one nucleus from each mate, and in C. cinereus, characteristic clamp connections at each septum. The dikaryon no longer produces oidia, but given the right temperature and light stimuli differentiates the fruiting bodies. The two different nuclei of the dikaryon fuse in special basidial cells on the undersurface of the mushroom and meiosis follows immediately. The nuclei produced enter the four basidiospores which develop on each basidium. A mature fruit body may have 108 basidia providing a vast potential for genetic recombination (2).KeywordsMating TypeTransactivation DomainHelical RegionMating Type GeneCompatible MatingThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

From pollination to fertilization in fruit trees

The phase that elapses from pollination to fertilization is re-examined giving special attention to pollen pistil interaction in compatible matings. Pollination induces an activation of the pistil. A number of changes take place in the different tissues of this organ that appear to support male gametophyte development and to assist fertilization. Thus pollination induces stigma secretion, the release of starch from the transmitting tissue and prolongs embryo sac viability. It appears that even those pollen grains that do not achieve fertilization have a synergistic role supporting others to do so. The pistil also has an effect on pollen tube growth. Pollen tube growth along the pistil is not continuous, accelerations and decelerations take place depending on the different tissues they traverse. The fact that pollen tube growth is heterotrophic, at the expenses of the pistil reserves, and that these reserves are not continuously produced confers the pistil with a role controlling pollen tube growth kinetics.

Cultural studies of four North American species of Perenniporia (Aphyllophorales: Polyporaceae)

Perenniporia phloiophila colonizes the dead, outer bark of live oak ( Quercus virginiana ) and is known in the southeastern United States on this host only. On 2% malt extract agar, P. phloiophila has an average growth rate of 5–6 mm day −1 at its optimum temperature range of 30–35 °C. P. phloiophila gives strong oxidase reactions on gallic and tannic acid agar media and does not produce chlamydospores in cultures of single dikaryons or homokaryons. P. medulla-panis has an average growth rate of 6–8 mm day −1 at its optimum temperature range of 30–35°. It has strong reactions on gallic and tannic acid agar media and produces chlamydospores in culture. Vegetative incompatibility between different dikaryotic isolates of P. phloiophila resulted in antagonistic hyphal interactions and dark pigmented zones between opposing isolates. Chlamydospores developed in the interaction zones of incompatible dikaryotic isolates. Self crosses of dikaryons resulted in complete intermingling of isolates with no interaction zone or pigmentation. Incompatible matings of homokaryotic isolates of P. phloiophila have abundant chlamydospores in the interaction zone while chlamydospores are absent in compatible matings of single spore isolates. Chlamydospores occur in all homokaryotic isolates of P. medulla-panis . Both species are heterothallic and tetrapolar. In vitro wood decay abilities of P. phloiophila, P. medulla-panis, P. ohiensis and P. fraxinophila were studied using wood of silverleaf oak, white fir and velvet ash. Percent weight loss (PWL) was greatest on silverleaf oak wood for three of the four species tested. P. medulla-panis caused the greatest PWL on white fir while P. fraxinophila caused the greatest PWL on silverleaf oak and velvet ash wood. Significant ( P = 0·05) differences in PWL occurred with P. phloiophila isolates tested at 25 and 30°. Mycelium of P. phloiophila readily colonized Emory oak bark blocks but only one isolate caused significant PWL.

Homokaryon-dikaryon phenotypic switching in an arginine requiring mutant of Coprinus congregatus

A homozygous arginine requiring mutant dikaryon of C. congregatus displays dramatic phenotype shifts in the absence of arginine. The mycelium grows as a phenotypic homokaryon (the homophase) in low-arginine media and as a phenotypic dikaryon (the diphase) in high-arginine media. The shift is complete, with the homophase and diphase having all the characteristics of wild-type homokaryons or dikaryons. The homophase contains nuclei of both compatible mating types but cannot grow as a diphase unless the concentration of arginine is 0·3 mM or higher. This suggests that the low concentration of arginine inhibits the expression and/or the function of the mating type genes and/or their products.

Intraspecific hybridization of Ustilago maydis haploids with compatible and incompatible mating type by electrofusion and genetic analysis of the fusion products

Two incompatibility loci,a andb, govern the life cycle ofUstilago maydis, the causative agent of corn smut. Until now it has not been possible to fuse two haploid strains homozygous at thea locus on nutrient media or via infection of the corn plant. The electrofusion method offers the opportunity to fuse both compatible and incompatibleU. maydis strains. To achieve close membrane contact, protoplasts of two different auxotrophic haploid strains were exposed to an inhomogeneous alternating electrical field (700 V/cm, 1.5 MHz). Cell fusion was observed by application of two field pulses (12 kV/cm, direct current; 7 μs duration). On selection medium, stable uninucleate prototrophs could be isolated. They exhibited twofold the DNA content per cell compared to the haploid strains—evidence for their diploidy. Four classes of diploids (a ≠ b ≠, a ≠ b =, a = b ≠, a = b =) could be constructed. They were identified by plate-mating with four haploid test strains on charcoal media.U. maydis diploids heterozygous at both incompatibility loci (a ≠ b ≠) or homozygous ata (a = b ≠) developed mycelial colonies, were pathogenic, and produced teliospores able to undergo meiosis. The diploids homozygous atb or at both loci (a ≠ b =, a = b =) formed yeastlike colonies and were nonpathogenic.

Laccaria fraterna, a common ectomycorrhizal fungus with mono- and bi-sporic basidia and multinucleate spores: comparison with the quadristerigmate, binucleate spored L. laccata and the hypogeous relative Hydnangium carneum

Examination of Laccaria collections from Western Australia revealed that the most common species L. fraterna had basidia which were monosporic, bisporic or very occasionally trisporic, in contrast to L. laccata which was quadrisporic. For L. fraterna, all post-meiotic nuclei migrated into the spores leaving basidia anucleate. Spores of monosterigmate basidia had four nuclei, and bisterigmate basidia usually had two. Post-meiotic mitosis occurred after spores were delimited and prior to morphological maturation. Mature spores had up to eight nuclei. That most spores had compatible mating-type nuclei was indicated by most single germinated spores having clamped mycelium with dikaryotic cells. In Hydnangium carneum, a hypogeous relative of Laccaria, post-meiotic mitosis occurred in the basidium and two nuclei migrated into each of the four spores. Migration patterns indicated that some spores had compatible mating-type nuclei, as in L. fraterna. Allocation of compatible mating types to spores partly explains why L. fraterna ‘weed-like’ behaviour and is a pioneer in plantations of eucalypts on former farmland or rehabilitated mine sites. Mycorrhizas of these fungi have been synthesized aseptically with several species of Eucalyptus.

Compatibility and Population Studies of Three Species ofTremella

Three species of Tremella are examined to document their mating compatibility system, confirm their identity as biological species, and define their population structures in terms of mating type allele frequency and distribution. Confirmation of intersterility was made by pairing Ax and A2 isolates of each of the three presumptive species in all possible combinations. No detectable reaction could be observed when interspecific haploid yeast cells were paired; all isolates intermingled but remained in a budding yeast phase. Isolates of the same species produced either clamped, dikaryotic mycelium or conjugation tubes whenever pairings involved unlike A alleles. Allele frequencies at the B locus were determined from sample populations for each species. Alleles were recovered in statistically equal frequencies from T. globospora and T indecorata, but significant departure from uniform allele fre? quency was observed in T moriformis. T. moriformis was isolated from ornamental tree species in Davis, California, and was not found outside the city. B allele diversity is significantly lower in this species than in other species ofthe genus. Due to the low allele diversity, an introduction of the fungus to the Davis area may have contained most ofthe alleles ofthe parental population. B allele frequency is not uniform and selective pressures over and above those associated with self-incompatibility may be responsible for this observed nonuniformity.