In the kingdom Fungi, the Glomeromycota is a newly-established phylum comprised of about species that live in close association with the roots of trees and plants. Fossil records indicate that trees and their root symbionts share a long evolutionary history.
It appears that most members of this family form arbuscular mycorrhizae: the hyphae interact with the root cells forming a mutually-beneficial association where the plants supply the carbon source and energy in the form of carbohydrates to the fungus while the fungus supplies essential minerals from the soil to the plant. This association is termed biotrophic. The Glomeromycota species that have arbuscular mycorrhizal are terrestrial and widely distributed in soils worldwide where they form symbioses with the roots of the majority of plant species.
They can also be found in wetlands, including salt-marshes, and are associated with epiphytic plants. Glyomeromycetes and tree roots : This image illustrates the bitrophic relationship between a glomeromycota Gigaspora margarita and the roots of a plant Lotus corniculatus. The glomeromycetes do not reproduce sexually and cannot survive without the presence of plant roots.
They have coenocytic hyphae and reproduce asexually, producing glomerospores. The biochemical and genetic characterization of the Glomeromycota has been hindered by their biotrophic nature, which impedes laboratory culturing.
This obstacle was eventually surpassed with the use of root cultures. With the advent of molecular techniques, such as gene sequencing, the phylogenetic classification of Glomeromycota has become clearer. This gene is highly conserved and commonly used in phylogenetic studies so it was isolated from spores of each taxonomic group.
Using a molecular clock approach based on the substitution rates of SSU sequences, scientists were able to estimate the time of divergence of the fungi. This analysis shows that all glomeromycetes probably descended from a common ancestor and million years ago, making them a monophyletic lineage. A long-held theory is that Glomeromycota were instrumental in the colonization of land by plants. Privacy Policy.
Skip to main content. Search for:. Classifications of Fungi. Chytridiomycota: The Chytrids Chytrids are the most primitive group of fungi and the only group that possess gametes with flagella. Learning Objectives Describe the ecology and reproduction of chytrids.
Key Takeaways Key Points The first recognizable chytrids appeared more than million years ago during the late pre-Cambrian period. Like protists, chytrids usually live in aquatic environments, but some species live on land.
Some chytrids are saprobes while others are parasites that may be harmful to amphibians and other animals. Chytrids reproduce both sexually and asexually, which leads to the production of zoospores. Chytrids have chitin in their cell walls; one unique group also has cellulose along with chitin. Chytrids are mostly unicellular, but multicellular organisms do exist. Key Terms chytridiomycete : an organism of the phylum Chytridiomycota zoospore : an asexual spore of some algae and fungi flagellum : a flagellum is a lash-like appendage that protrudes from the cell body of certain prokaryotic and eukaryotic cells coenocytic : a multinucleate cell that can result from multiple nuclear divisions without their accompanying cytokinesis.
Zygomycota: The Conjugated Fungi Zygomycota, a small group in the fungi kingdom, can reproduce asexually or sexually, in a process called conjugation. Learning Objectives Describe the ecology and reproduction of Zygomycetes. Key Takeaways Key Points Most zygomycota are saprobes, while a few species are parasites. Zygomycota usually reproduce asexually by producing sporangiospores. Zygomycota reproduce sexually when environmental conditions become unfavorable.
To reproduce sexually, two opposing mating strains must fuse or conjugate, thereby, sharing genetic content and creating zygospores. The resulting diploid zygospores remain dormant and protected by thick coats until environmental conditions have improved.
When conditions become favorable, zygospores undergo meiosis to produce haploid spores, which will eventually grow into a new organism. Key Terms zygomycete : an organism of the phylum Zygomycota karyogamy : the fusion of two nuclei within a cell zygospore : a spore formed by the union of several zoospores conjugation : the temporary fusion of organisms, especially as part of sexual reproduction.
Ascomycota: The Sac Fungi Most fungi belong to the Phylum Ascomycota, which uniquely forms of an ascus, a sac-like structure that contains haploid ascospores.
Learning Objectives Describe the ecology and the reproduction of Ascomycetes. Key Takeaways Key Points Ascomycota fungi are the yeasts used in baking, brewing, and wine fermentation, plus delicacies such as truffles and morels. Ascomycetes are filamentous and produce hyphae divided by perforated septa. Ascomycetes frequently reproduce asexually which leads to the production of conidiophores that release haploid conidiospores.
The antheridium and the ascogonium combine in plasmogamy at the time of fertilization, followed by nuclei fusion in the asci. In the ascocarp, a fruiting body, thousands of asci undergo meiosis to generate haploid ascospores ready to be released to the world. Basidiomycota: The Club Fungi The basidiomycota are mushroom-producing fungi with developing, club-shaped fruiting bodies called basidia on the gills under its cap. Learning Objectives Describe the ecology and reproduction of the Basidiomycota.
The basidiomycota includes shelf fungus, toadstools, and smuts and rusts. Unlike most fungi, basidiomycota reproduce sexually as opposed to asexually. Two different mating strains are required for the fusion of genetic material in the basidium which is followed by meiosis producing haploid basidiospores.
Mycelia of different mating strains combine to produce a secondary mycelium that contains haploid basidiospores in what is called the dikaryotic stage, where the fungi remains until a basidiocarp mushroom is generated with the developing basidia on the gills under its cap. Key Terms basidiocarp : a fruiting body that protrudes from the ground, known as a mushroom, which has a developing basidia on the gills under its cap basidiomycete : a fungus of the phylum Basidiomycota, which produces sexual spores on a basidium Basidiomycota : a taxonomic division within the kingdom Fungi: 30, species of fungi that produce spores from a basidium basidium : a small structure, shaped like a club, found in the Basidiomycota phylum of fungi, that bears four spores at the tips of small projections basidiospore : a sexually-reproductive spore produced by fungi of the phylum Basidiomycota.
Deuteromycota: The Imperfect Fungi Phylum Deuteromycota is a polyphyletic group of asexually-reproducing fungi that do not display a sexual phase; they are known as imperfect. Learning Objectives Describe the ecology and reproduction of the Deuteromycota.
Key Takeaways Key Points Deuteromycota do not possess the sexual structures that are used to classify other fungi. These mycelia can produce two types of reproductive structures. First, they can produce conidiophores for asexual reproduction.
Conidiaphores may simply branch off from the mycelia or they may be formed in fruiting bodies. Secondly, ascomycota produce structures for sexual reproduction called gametangia. These structures are either male or female. The male gametangia may be anything from a detached cell called a spermatium to a differentiated region called an antheridium. The female structure is always a differentiated region known as the ascogonium.
Many Ascomycota form a fruiting body, or ascoma, similar to that of the Basidiomycota, but with an important difference. The ascomycota fruiting body is composed mainly of entangled monokaryotic hyphae from the male and female mycelia rather than of dikaryotic hyphae formed from the joining of hyphae from the two mycelia, as in the basidiomycota. The only dikaryotic structures in the fruiting body are those produced by the gametangia after plasmogamy.
The exceptions to the above discussion of structure are the unicellular ascomycota or yeasts. These organisms are non-motile single cells with chitinous cell walls that earn them classification as fungi.
Though they mainly reproduce by budding and fission, yeasts also engage in sexual reproduction that results in the production of an ascus, placing them in the Ascomycota. Most varieties of yeast do not form multicellular filiments like the mycelia and hyphae of other fungi, though they do live in massive groupings called colonies. Aspergillus oryzae is used in the fermentation of rice to produce sake. Other ascomycetes parasitize plants and animals, including humans.
For example, fungal pneumonia poses a significant threat to AIDS patients who have a compromised immune system. Ascomycetes not only infest and destroy crops directly, they also produce poisonous secondary metabolites that make crops unfit for consumption.
Filamentous ascomycetes produce hyphae divided by perforated septa, allowing streaming of cytoplasm from one cell to the other. Conidia and asci, which are used respectively for asexual and sexual reproductions, are usually separated from the vegetative hyphae by blocked non-perforated septa.
Asexual reproduction is frequent and involves the production of conidiophores that release haploid conidiospores.
0コメント