Glomeromycota
Encyclopedia
Glomeromycota is one of seven currently recognized phyla within the kingdom
Fungi, with approximately 230 described species. Members of the Glomeromycota form arbuscular mycorrhiza
s (AMs) with the roots or thalli (e.g. in bryophyte
s) of land plants. Geosiphon pyriformis forms an endocytobiotic association with Nostoc
cyanobacteria. AM formation has not yet been shown for all species. The majority of evidence shows that the Glomeromycota are obligate biotrophs, dependent on symbiosis with land plants (Nostoc in the case of Geosiphon) for carbon and energy, but there is recent circumstantial evidence that some species may be able to lead an independent existence. The arbuscular mycorrhiza
l species are terrestrial and widely distributed in soils worldwide where they form symbioses with the roots of the majority of plant species (>80%). They can also be found in wetlands, including salt-marshes, and associated with epiphytic plants.
(occasionally sparsely septate) mycelia and reproduce asexually through blastic development of the hyphal tip to produce spore
s (Glomerospores) with diameters of 80-500μm. In some, complex spores form within a terminal saccule.
l attachment and reaction to staining compounds allowed a phylogeny to be constructed. Superficial similarities led to the initial placement of genus Glomus in the unrelated family Endogonaceae. Following broader reviews that cleared up the sporocarp confusion, the Glomeromycota were first proposed in the genera Acaulospora and Gigaspora before being accorded their own order with the three families
Glomaceae (now Glomeraceae), Acaulosporaceae and Gigasporaceae.
With the advent of molecular techniques this classification has undergone major revision. An analysis of small subunit (SSU) rRNA sequences indicated that they share a common ancestor with the Dikarya
.
Several species which produce glomoid spores (i.e. spores similar to Glomus
) in fact belong to other deeply divergent lineages and were placed in the orders, Paraglomerales
and Archaeosporales
. This new classification includes the Geosiphonaceae, which presently contains one fungus (Geosiphon pyriformis) that forms endosymbiotic associations with the cyanobacterium Nostoc punctiforme and produces spores typical to this phylum, in the Archaeosporales
.
Work in this field is incomplete, and members of Glomus may be better suited to different genera or families.
(SSU rRNA). This gene is highly conserved and commonly used in phylogenetic
studies so was isolated from spore
s of each taxonomic
group before amplification through the polymerase chain reaction
(PCR). A molecular clock
approach, based on the substitution rates of SSU sequences, was used to estimate the time of divergence of the fungi. The molecular analysis found that they are between 462 and 353 million years old. The data enforces the long-held theory that they were instrumental in the colonization of land by plants.
Kingdom (biology)
In biology, kingdom is a taxonomic rank, which is either the highest rank or in the more recent three-domain system, the rank below domain. Kingdoms are divided into smaller groups called phyla or divisions in botany...
Fungi, with approximately 230 described species. Members of the Glomeromycota form arbuscular mycorrhiza
Arbuscular mycorrhiza
An arbuscular mycorrhiza is a type of mycorrhiza in which the fungus penetrates the cortical cells of the roots of a vascular plant....
s (AMs) with the roots or thalli (e.g. in bryophyte
Bryophyte
Bryophyte is a traditional name used to refer to all embryophytes that do not have true vascular tissue and are therefore called 'non-vascular plants'. Some bryophytes do have specialized tissues for the transport of water; however since these do not contain lignin, they are not considered to be...
s) of land plants. Geosiphon pyriformis forms an endocytobiotic association with Nostoc
Nostoc
Nostoc is a genus of cyanobacteria found in a variety of environmental niches that forms colonies composed of filaments of moniliform cells in a gelatinous sheath.The name "Nostoc" was invented by Paracelsus...
cyanobacteria. AM formation has not yet been shown for all species. The majority of evidence shows that the Glomeromycota are obligate biotrophs, dependent on symbiosis with land plants (Nostoc in the case of Geosiphon) for carbon and energy, but there is recent circumstantial evidence that some species may be able to lead an independent existence. The arbuscular mycorrhiza
Arbuscular mycorrhiza
An arbuscular mycorrhiza is a type of mycorrhiza in which the fungus penetrates the cortical cells of the roots of a vascular plant....
l species are terrestrial and widely distributed in soils worldwide where they form symbioses with the roots of the majority of plant species (>80%). They can also be found in wetlands, including salt-marshes, and associated with epiphytic plants.
Reproduction
The Glomeromycota have generally coenocyticCoenocyte
A coenocyte is a multinucleate cell. It can result from multiple nuclear divisions without accompanying cell divisions, or from cellular aggregation followed by dissolution of the cell membranes inside the mass. Coenocytes are found in fungi and some protists, such as algae and slime mold. Some...
(occasionally sparsely septate) mycelia and reproduce asexually through blastic development of the hyphal tip to produce spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s (Glomerospores) with diameters of 80-500μm. In some, complex spores form within a terminal saccule.
Phylogeny
Initial studies of the Glomeromycota were based on the morphology of soil-borne sporocarps (spore clusters) found in or near colonized plant roots. Distinguishing features such as wall morphologies, size, shape, color, hyphaHypha
A hypha is a long, branching filamentous structure of a fungus, and also of unrelated Actinobacteria. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium; yeasts are unicellular fungi that do not grow as hyphae.-Structure:A hypha consists of one or...
l attachment and reaction to staining compounds allowed a phylogeny to be constructed. Superficial similarities led to the initial placement of genus Glomus in the unrelated family Endogonaceae. Following broader reviews that cleared up the sporocarp confusion, the Glomeromycota were first proposed in the genera Acaulospora and Gigaspora before being accorded their own order with the three families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Glomaceae (now Glomeraceae), Acaulosporaceae and Gigasporaceae.
With the advent of molecular techniques this classification has undergone major revision. An analysis of small subunit (SSU) rRNA sequences indicated that they share a common ancestor with the Dikarya
Dikarya
Dikarya is a subkingdom of Fungi that includes the phyla Ascomycota and Basidiomycota, both of which in general produce dikaryons, may be filamentous or unicellular, but are always without flagella. The Dikarya are most of the so called "higher fungi", but also include many anamorphic species that...
.
Several species which produce glomoid spores (i.e. spores similar to Glomus
Glomus (fungus)
Glomus is a genus of arbuscular mycorrhizal fungi, and all species form symbiotic relationships with plant roots. Glomus is the largest genus of AM fungi, with ca. 85 species described, but as currently defined is non-monophyletic.-Classification:Glomus is the only genus in the family...
) in fact belong to other deeply divergent lineages and were placed in the orders, Paraglomerales
Paraglomerales
The Paraglomerales are a group of exclusively hypogeous arbuscular mycorrhizal fungi that rarely produce vesicles and reproduce through unpigmented spores....
and Archaeosporales
Archaeosporales
Archaeosporales is an order of fungi that may form arbuscular mycorrhiza or endocytosymbioses with cyanobacteria....
. This new classification includes the Geosiphonaceae, which presently contains one fungus (Geosiphon pyriformis) that forms endosymbiotic associations with the cyanobacterium Nostoc punctiforme and produces spores typical to this phylum, in the Archaeosporales
Archaeosporales
Archaeosporales is an order of fungi that may form arbuscular mycorrhiza or endocytosymbioses with cyanobacteria....
.
Work in this field is incomplete, and members of Glomus may be better suited to different genera or families.
Molecular biology
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. The first mycorrhizal gene to be sequenced was the small-subunit ribosomal RNARibosomal RNA
Ribosomal ribonucleic acid is the RNA component of the ribosome, the enzyme that is the site of protein synthesis in all living cells. Ribosomal RNA provides a mechanism for decoding mRNA into amino acids and interacts with tRNAs during translation by providing peptidyl transferase activity...
(SSU rRNA). This gene is highly conserved and commonly used in phylogenetic
Phylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
studies so was isolated from spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s of each taxonomic
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
group before amplification through the polymerase chain reaction
Polymerase chain reaction
The polymerase chain reaction is a scientific technique in molecular biology to amplify a single or a few copies of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence....
(PCR). A molecular clock
Molecular clock
The molecular clock is a technique in molecular evolution that uses fossil constraints and rates of molecular change to deduce the time in geologic history when two species or other taxa diverged. It is used to estimate the time of occurrence of events called speciation or radiation...
approach, based on the substitution rates of SSU sequences, was used to estimate the time of divergence of the fungi. The molecular analysis found that they are between 462 and 353 million years old. The data enforces the long-held theory that they were instrumental in the colonization of land by plants.
External links
- Tree of Life Glomeromycota
- Glomeromycota at the International Culture Collection of VA Mycorrhizal FungiMycorrhizaA mycorrhiza is a symbiotic association between a fungus and the roots of a vascular plant....
(INVAM) - Glomeromycota at the University of SydneyUniversity of SydneyThe University of Sydney is a public university located in Sydney, New South Wales. The main campus spreads across the suburbs of Camperdown and Darlington on the southwestern outskirts of the Sydney CBD. Founded in 1850, it is the oldest university in Australia and Oceania...
Fungal BiologyBiologyBiology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
s|ite - 'AMF-phylogeny' - 'Glomeromycota database' web-site at the University of Munich