Glomeromycota (informally
glomeromycetes) is one of seven currently recognized phyla within the
kingdomIn biological taxonomy, kingdom and/or regnum is a taxonomic rank in either the highest rank, or the rank below domain. Each kingdom is divided into smaller groups called phyla...
Fungi, with approximately 200 described species. Members of the Glomeromycota form
arbuscular mycorrhizaAn 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
bryophyteBryophytes are all embryophytes that are non-vascular: they have tissues and enclosed reproductive systems, but they lack vascular tissue that circulates liquids. They neither have flowers nor produce seeds, reproducing via spores...
s) of land plants.
Geosiphon pyriformis forms an endocytobiotic association with
NostocNostoc is a genus of fresh water cyanobacteria that forms spherical colonies composed of filaments of moniliform cells in a gelatinous sheath. When on the ground, a Nostoc colony is ordinarily not seen; but after a rain it swells up into a conspicuous jellylike mass, which was once thought to have...
cyanobacteria. AM formation has not yet been shown for all species.
Glomeromycota (informally
glomeromycetes) is one of seven currently recognized phyla within the
kingdomIn biological taxonomy, kingdom and/or regnum is a taxonomic rank in either the highest rank, or the rank below domain. Each kingdom is divided into smaller groups called phyla...
Fungi, with approximately 200 described species. Members of the Glomeromycota form
arbuscular mycorrhizaAn 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
bryophyteBryophytes are all embryophytes that are non-vascular: they have tissues and enclosed reproductive systems, but they lack vascular tissue that circulates liquids. They neither have flowers nor produce seeds, reproducing via spores...
s) of land plants.
Geosiphon pyriformis forms an endocytobiotic association with
NostocNostoc is a genus of fresh water cyanobacteria that forms spherical colonies composed of filaments of moniliform cells in a gelatinous sheath. When on the ground, a Nostoc colony is ordinarily not seen; but after a rain it swells up into a conspicuous jellylike mass, which was once thought to have...
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 mycorrhizaAn 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
coenocyticA 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...
(occasionally sparsely septate) mycelia and reproduce asexually through blastic development of the hyphal tip to produce
sporeIn biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions...
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,
hyphaA hypha is a long, branching filamentous cell 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 more...
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
familiesIn 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...
Glomaceae (now
GlomeraceaeA family of fungi within the order Glomerales.-Characteristics:Distinguished by:*Vesicle formation to create internal spores*Chlamydospore formation-Spelling:...
), 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
DikaryaDikarya 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
GlomusGlomus 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. 90 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,
ParaglomeralesThe Paraglomerales are a group of exclusively hypogeous arbuscular mycorrhizal fungi that rarely produce vesicles and reproduce thourgh unpigmented spores....
and
ArchaeosporalesArchaeosporales is an order of fungi that may form arbuscular mycorrhiza or endocytosymbioses with cyanobacteria....
. This new classification includes the
GeosiphonaceaeThe Geosiphonaceae are a family of fungi in the order Archaeosporales. The family consists of one genera, Geosiphon, containing one species, Geosiphon pyriforme, which forms an association with the cyanobacteria Nostoc....
, 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
ArchaeosporalesArchaeosporales 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 is the central component of the ribosome, the protein manufacturing machinery of all living cells. The function of the rRNA is to provide a mechanism for decoding mRNA into amino acids and to interact with the tRNAs during translation by providing peptidyl transferase activity.The...
(SSU rRNA). This gene is highly conserved and commonly used in
phylogeneticIn biology, phylogenetics is the study of evolutionary relatedness among various groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
studies so was isolated from
sporeIn biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions...
s of each
taxonomicTaxonomy is the practice and science of classification. The word finds its roots in the Greek , taxis and , nomos...
group before amplification through the
polymerase chain reactionIn molecular biology, the polymerase chain reaction is a technique to amplify a single or 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 clockThe molecular clock is a technique in molecular evolution which 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 Fungi
A mycorrhiza is a symbiotic association between a fungus and the roots of a plant. In a mycorrhizal association, the fungus may colonize the roots of a host plant, either intracellularly or extracellularly...
(INVAM)
- Glomeromycota at the University of Sydney
The University of Sydney is the oldest university in Australia. It was established in Sydney in 1850. It is a member of Australia's "Group of Eight" universities that are highly ranked in terms of their research performance...
Fungal BiologyBiology is the natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy...
s|ite
- 'AMF-phylogeny' - 'Glomeromycota database' web-site at the University of Munich