Fertile Spores Research Articles

Stimulation of asymbiotic sporulation in arbuscular mycorrhizal fungi by fatty acids.

Arbuscular mycorrhizal (AM) fungi are obligate symbionts that depend on living host plants to complete their life cycle1,2. This feature, which leads to their unculturability in the absence of plants, strongly hinders basic research and agricultural application of AM fungi. However, at least one AM fungus can grow and develop fertile spores independently of a host plant in co-culture with the bacterium Paenibacillus validus3. The bacteria-derived substances are thought to act as stimulants or nutrients for fungal sporulation, but these molecules have not been identified. Here, we show that (S)-12-methyltetradecanoic acid4,5, a methyl branched-chain fatty acid isolated from bacterial cultures, stimulates the branching of hyphae germinated from mother spores and the formation of secondary spores in axenic culture of the AM fungus Rhizophagus irregularis. Extensive testing of fatty acids revealed that palmitoleic acid induces more secondary spores than the bacterial fatty acid in R. irregularis. These induced spores have the ability to infect host plant roots and to generate daughter spores. Our work shows that, in addition to a major source of organic carbon6-9, fatty acids act as stimulants to induce infection-competent secondary spores in the asymbiotic stage and could provide the key to developing the axenic production of AM inoculum.

Evidence for amphithallism and broad geographical hybridization potential among Agaricus subrufescens isolates from Brazil, France, and Thailand

Agaricus subrufescens is a cultivated edible and medicinal mushroom. Its known geographical distribution encompasses the Americas, Europe, Oceania, and Asia. The objective of this study was to assess mating compatibility and interfertility of strains originating from Brazil, France, and Thailand. Progeny of each strain were analyed with codominant molecular markers. Multilocus genotype tests revealed that the three strains were amphithallic with percentages of heterokaryotic single spore progenies of 75 % for the Thai strain and around 40 % for the Brazilian and French strains. In mating tests A. subrufescens had a multiallelic unifactorial system of sexual incompatibility. The three parent strains were interfertile based on experimental pairings of single-spore isolates, the recovery of hybrid heterokaryons from compatible matings, and the ability of hybrids to produce mushrooms and fertile spores. This biological approach supports the inclusion of the European strains within the species and the extension of the geographical distribution range to Asia. Our data should help to develop breeding strategies and to better manage and exploit the diversity existing in A. subrufescens.

Two types of partial fertility in a diploid population of the fern Thelypteris decursive-pinnata (Thelypteridaceae)

Two types of abnormal sporophytes were observed in a population of diploid Thelypteris decursive-pinnata. Most sporophytes in this population exhibited regular chromosome pairing, resulting in the formation of 30 bivalents in meiosis I; however, they produced abortive spores to various degrees. Some formed large globose spores at low frequencies, most likely to be unreduced diplospores. The other type of abnormal sporophyte underwent synaptic failure to form 60 univalents at meiosis I, but produced fertile spores, mostly large globose ones at low frequencies. The globose spores were considered unreduced diplospores because the gametophytes arising from them produced tetraploid sporophytes by gametophytic selfing. One tetraploid formed only univalents at meiosis I. Allozyme variation was not detected in this population, although neighboring ordinary diploid populations exhibited it to a certain degree. The sympatric occurrence and allozyme uniformity of the two groups suggest that both are offspring of a founder sporophyte, which may have possessed two types of mutated recessive genes responsible for the spore sterility and the synaptic failure in meiosis. Unreduced spores formed by these two types may play an important role in the polyploid speciation of this species.

Cost of movement in the multicellular stage of the social amoebae Dictyostelium discoideum and D. purpureum

One of the challenges of microbial life is that the best location for feeding and growth may not be the best location for dispersal. This is likely to be the case for the social amoebae Dictyostelium discoideum and Dictyostelium purpureum that feed on soil bacteria in the amoeba stage, but then group into a multicellular slug that moves towards light before forming a fruiting body. Here we examine this short-range social dispersal in the social amoebae, Dictyostelium discoideum and D. purpureum. We predicted D. purpureum would have higher migration costs and travel less far because it forms a dead stalk from living cells as it moves, while D. discoideum delays stalk formation until movement ceases. We found that D. purpureum migrated shorter distances than D. discoideum, in accord with our prediction. D. discoideum slugs moved an average of 2.46 ± 0.19 cm while D. purpureum slugs moved an average of 1.04 ± 0.06 cm. In both species, migration incurred a cost in reduced spore production, compared to experimental conditions where slugs did not migrate. D. discoideum under the no migration treatment produced 0.55± 0.05 spores per cell and under the migration treatment produced 0.25 ± 0.04 spores per cell. D. purpureum under the no migration treatment produced 1.01± 0.06 spores per cell and under the migration treatment produced 0.85 ± 0.06 spores per cell. We also found that D. discoideum produced fruiting bodies with fewer spores after migrating while D. purpureum did not. It appears that the evolutionary loss of stalked migration gives D. discoideum cells the advantage of delaying specialization and the ability to colonize more distant locations, but has significant costs due to migration distance, such as the fraction of cells that become fertile spores.

How social evolution theory impacts our understanding of development in the social amoebaDictyostelium

Dictyostelium discoideum has been very useful for elucidating principles of development over the last 50 years, but a key attribute means there is a lot to be learned from a very different intellectual tradition: social evolution. Because Dictyostelium arrives at multicellularity by aggregation instead of through a single-cell bottleneck, the multicellular body could be made up of genetically distinct cells. If they are genetically distinct, natural selection will result in conflict over which cells become fertile spores and which become dead stalk cells. Evidence for this conflict includes unequal representation of two genetically different clones in spores of a chimera, the poison-like differentiation inducing factor (DIF) system that appears to involve some cells forcing others to become stalk, and reduced functionality in migrating chimeras. Understanding how selection operates on chimeras of genetically distinct clones is crucial for a comprehensive view of Dictyostelium multicellularity. In nature, Dictyostelium fruiting bodies are often clonal, or nearly so, meaning development will often be very cooperative. Relatedness levels tell us what benefits must be present for sociality to evolve. Therefore it is important to measure relatedness in nature, show that it has an impact on cooperation in the laboratory, and investigate genes that Dictyostelium uses to discriminate between relatives and non-relatives. Clearly, there is a promising future for research at the interface of development and social evolution in this fascinating group.

Cheating does not explain selective differences at high and low relatedness in a social amoeba

BackgroundAltruism can be favored by high relatedness among interactants. We tested the effect of relatedness in experimental populations of the social amoeba Dictyostelium discoideum, where altruism occurs in a starvation-induced social stage when some amoebae die to form a stalk that lifts the fertile spores above the soil facilitating dispersal. The single cells that aggregate during the social stage can be genetically diverse, which can lead to conflict over spore and stalk allocation. We mixed eight genetically distinct wild isolates and maintained twelve replicated populations at a high and a low relatedness treatment. After one and ten social generations we assessed the strain composition of the populations. We expected that some strains would be out-competed in both treatments. In addition, we expected that low relatedness might allow the persistence of social cheaters as it provides opportunity to exploit other strains.ResultsWe found that at high relatedness a single clone prevailed in all twelve populations. At low relatedness three clones predominated in all twelve populations. Interestingly, exploitation of some clones by others in the social stage did not explain the results. When we mixed each winner against the pool of five losers, the winner did not prevail in the spores because all contributed fairly to the stalk and spores. Furthermore, the dominant clone at high-relatedness was not cheated by the other two that persisted at low relatedness. A combination of high spore production and short unicellular stage most successfully explained the three successful clones at low relatedness, but not why one of them fared better at high relatedness. Differences in density did not account for the results, as the clones did not differ in vegetative growth rates nor did they change the growth rates over relevant densities.ConclusionsThese results suggest that social competition and something beyond solitary growth differences occurs during the vegetative stage when amoebae eat bacteria and divide by binary fission. The high degree of repeatability of our results indicates that these effects are strong and points to the importance of new approaches to studying interactions in D. discoideum.

Reproducible and controllable light induction of in vitro fruiting of the white-rot basidiomycete Pleurotus ostreatus

Fruiting is a crucial developmental process in basidiomycetes yet the genetic and molecular factors that control it are not yet fully understood. The search for fruiting inducers is of major relevance for both basic research and for their use in industrial applications. In this paper, an efficient and reproducible protocol for controlled fruiting induction of Pleurotus ostreatus growing on synthetic medium is described. The protocol is based on the control of light intensity and photoperiod and permits the life cycle for this fungus to be completed in less than two weeks. The fruiting bodies produced by this method release fertile spores after 4–5 d of culture. Our results indicate that fruiting induction is solely dependent on the illumination regime and that it occurs long before the available nutrients are depleted in the culture. This protocol will greatly facilitate molecular and developmental biology research in this fungus as it avoids the need for complex culture media based on lignocellulosic materials or the use of chemical inducers.

The bacteriumPaenibacillus validusstimulates growth of the arbuscular mycorrhizal fungusGlomus intraradicesup to the formation of fertile spores

Two isolates of Paenibacillus validus (DSM ID617 and ID618) stimulated growth of the arbuscular mycorrhizal fungus Glomus intraradices Sy167 up to the formation of fertile spores, which recolonize carrot roots. Thus, the fungus was capable of completing its life cycle in the absence of plant roots, but relied instead on the simultaneous growth of bacteria. The supernatant of a mixed batch culture of the two P. validus isolates contained raffinose and another, unidentified trisaccharide. Among the oligosaccharides tested, raffinose was most effective in stimulating hyphal mass formation on plates but could not promote growth to produce fertile spores. A suppressive subtractive hybridization library followed by reverse Northern analyses indicated that several genes with products involved in signal transduction are differentially expressed in G. intraradices SY 167 when grown in coculture with P. validus (DSM 3037). The present investigation, while likely representing a significant step forward in understanding the arbuscular mycorrhizal fungus symbioses, also confirms that its optimal establishing and functioning might rely on many, as yet unidentified factors.

Sporogenesis in Haploid Sporophytes of Osmunda japonica (Osmundaceae)

Three out of four haploid sporophytes of Osmunda japonica (2n=x=22), produced artificially by induction of apogamy, developed fertile fronds and spores. The spores that germinated (up to 25% of the total green spores) were monoploid, determined by the nuclear DNA content and the somatic chromosome numbers of the gametophytes. The haploid 2 sporophyte produced more fertile spores than the two other haploids, providing an opportunity to observe the details of fertile spore development. In some spore mother cells of this plant, the random separation of 22 univalent chromosomes did not occur at the first meiotic division, but restitution nuclei were formed. The observation of chromosome behavior in the haploid 2 sporophyte showed that sporogenesis in haploid O. japonica resembles the Braithwaite scheme in apogamous ferns. Gametophytes, developed from spores of the three haploid sporophytes, produced a few sporophytes with diploid chromosome numbers. One of the new sporophytes was trisomic.

The yeast lifecycle and DNA array technology.

The genome variability and meiotic gene expression patterns in two unrelated laboratory yeast strains, SK1 and W303, have been characterized using high-density oligonucleotide arrays. The statistical analysis and comparison of the data has allowed identification of: (1) genes with functional importance to meiosis and sporulation in yeast and (2) genes expressed in a strain-specific manner. The genome-wide data also reveal potential reasons why these strains display significant differences in the ability to make fertile spores. Molecularly tagged yeast deletion strains have been used to determine the contribution of each gene to the execution of the sporulation/germination pathway. The application of genetics and the new genomic technologies have allowed a quantum jump in our understanding of yeast molecular biology.

The yeast lifecycle and DNA array technology

The genome variability and meiotic gene expression patterns in two unrelated laboratory yeast strains, SK1 and W303, have been characterized using high-density oligonucleotide arrays. The statistical analysis and comparison of the data has allowed identification of: (1) genes with functional importance to meiosis and sporulation in yeast and (2) genes expressed in a strain-specific manner. The genome-wide data also reveal potential reasons why these strains display significant differences in the ability to make fertile spores. Molecularly tagged yeast deletion strains have been used to determine the contribution of each gene to the execution of the sporulation/germination pathway. The application of genetics and the new genomic technologies have allowed a quantum jump in our understanding of yeast molecular biology. Journal of Industrial Microbiology & Biotechnology (2002) 28, 186–191 DOI: 10.1038/sj/jim/7000200

Evolution of Boston Fern Varieties

Accurate records of the origin of the Boston fern (Nephrolepis exaltata bostoniensis) and its many varieties compose one of the most complete histories of any cultivated plant. The Boston fern mutation was discovered among 200 Sword ferns by a florist near Boston in 1895. The Sword fern (Nephrolepis exaltata) is native in Florida and throughout the American tropics. This wild species was introduced at Kew in 1793 from Jamaica. For 100 years it remained stable, and by 1895 it was used widely as a house plant. The Boston fern was more desirable as a house plant, and gradually replaced the wild species almost entirely. Benedict (1916) estimated that from 1,000,000 to 2,000,000 Boston fern plants are propagated each year in the United States., Plants from the southern states, and from the western, northern, or central part of the country, could not be distinguished from those of eastern Massachusetts. However, six exceptions to this statement must be nioted. Within a few years of each other there appeared in the greenhouses of commercial growers in five states, amid countless thousands of normal Boston ferns, six mutations now known as Scott's fern (Scotti), Giatra's fern (Giatrasi), Pierson's fern (Piersoni), Foster's fern (Fosteri), Harris' fern (Harrisi), and the Roosevelt fern (Rooseveltti). From these six mutants numerous other varieties have been derived, many of which have not been named. Within the 45 years since the Boston fern appeared, over 200 varieties have come into existence, many gaining commercial importance. Some of the noteworthy facts concerning these numerous mutants are as follows: 1. From what was originally a stable species a mutant (Boston fern) was discovered among thousands of Sword fern plants after the species had been cultivated for about 100 years. 2. The wild species (Nephrolepis exaltata) produces fertile spores, but the Boston fern and all of the derived varieties are sterile, except one (Nephrolepis exaltata bostoniensis f ertilis). Fertilis was a mutant from Piersoni. 3. The Boston fern is of such a xerophytic type that it can withstand the dry atmosphere of the average home-which is drier than desert air. The other extreme is reached in a form which must be kept in a saturated atmosphere to keep it alive. 4. One variety, elegantissima-compacta 1 Papers from the Department of Botany, The Ohio State University, No. 425.

The Growth of Dictyostelium discoideum upon Pathogenic Bacteria

Species of the Dictyosteliaceae, a group of pseudoplasmodiumforming slime molds, are not uncommon in nature and can be readily isolated from soils, from decaying vegetation and from the dung of various animals. In contrast to the Myxogastrales which possess true plasmodia, the Dictyosteliaceae are characterized by myxamoebae which retain their identity throughout the whole life cycle of the organisms. During the vegetative stage these myxamoebae are free-living and feed by the ingestion and digestion of bacterial cells. With the exhaustion of the available food supply, the myxamoebae collect into aggregates termed pseudoplasmodia, and collectively build fruiting structures, or sorocarps. In these structures some myxamoebae become transformed into sterile, supportive cells to form a stalk, or sorophore, while others become differentiated into fertile spores forming a spore head, or sorus. The ubiquitous species Dictyostelium mucoroides Bref. has been more widely studied than other members of the group and from the work of Vuillemin (1902), Potts (1902), Pinoy (1903 and 1907), and Schuckmann (1924) a limited bacterial host range embracing twelve different species has been reported for it.