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'Glomeromycota' (informally 'glomeromycetes') is one of six currently recognized phyla within the kingdom Fungi
A higher level phylogenetic classification of the ''Fungi'', Hibbett, D.S., ''et al.'', , , Mycol. Res., 2007
, with approximately 200 described species.^[1] With the exception of ''Geosiphon pyriformis'', which forms an endocytobiotic association with Nostoc cyanobacteria^[2], all species are thought to form arbuscular mycorrhizas with the roots of land plants. However, this 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^[3]. The arbuscular mycorrhizal species 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 associated with epiphytic plants.

Contents

Reproduction

Phylogeny

Molecular biology

See also

References

External links

Reproduction

The Glomeromycota have generally coenocytic (occasionally sparsely septate) mycelia and reproduce asexually through blastic development of the hyphal tip to produce spores 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.^[4] Distinguishing features such as wall morphologies, size, shape, color, hyphal attachment and reaction to staining compounds allowed a phylogeny to be constructed.Wright, S.F. Management of Arbuscular Mycorrhizal Fungi. 2005. In Roots and Soil Management: Interactions between roots and the soil. Ed. Zobel, R.W., Wright, S.F. USA: American Society of Agronomy. Pp 183-197. Superficial similarities led to the initial placement of genus ''Glomus'' in the unrelated family ''Endogonaceae''.^[5] Following broader reviews that cleared up the sporocarp confusion, the Glomeromycota were first proposed in the genera ''Acaulospora'' and ''Gigaspora''^[6] before being accorded their own order with the three families ''Glomaceae'' (now ''Glomeraceae''), ''Acaulosporaceae'' and ''Gigasporaceae''.^[7]
With the advent of molecular techniques this classification has undergone major revision, laying to rest doubts in the group's monophyly.^[8] An analysis of small subunit (SSU) rRNA sequences^[9] indicated that they share a common ancestor with the Dikarya while the Endogonaceae are late branchers off the chytrid lineage.
Several species which produce glomoid spores (i.e. spores similar to ''Glomus'') in fact belong to other deeply divergent lineages^[10] and were placed in the orders, Paraglomerales and Archaeosporales. This new classification includes the ''Geosiphonaceae'' in the ''Archaeosporales'' which presently contains one fungus that forms endosymbiotic associations with the cyanobacterium ''Nostoc punctiforme'' Molecular phylogeny, taxonomy, and evolution of Geosiphon pyriformis and arbuscular mycorrhizal fungi, Schüßler, A., , , Plant and Soil, 2002 and produces spores typical to this phylum.
Work in this field is incomplete, and members of ''Glomus'' may be better suited to different genera^[11] or families.
Origin and diversification of endomycorrhizal fungi and coincidence with vascular land plants, Simon, L., Bousquet, J., Levesque, C., Lalonde, M., , , Nature, 1993

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 RNA (SSU rRNA).^[12] This gene is highly conserved and commonly used in phylogenetic studies so was isolated from spores 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.^[13]

See also

References

1. http://www.lrz-muenchen.de/~schuessler/amphylo/amphylogeny.html
2. http://www.lrz-muenchen.de/~schuessler/geosiphon/geosiphon.html
3.
Differences in the species composition of arbuscular mycorrhizal fungi in spore, root and soil communities in a grassland ecosystem, Hempel, S., Renker, C. & Buscot, F., , , Environmental Microbiology, 2007

4.
Fungi nonnulli hipogaei, novi v. minus cogniti auct, Tulasne, L.R., & C. Tulasne, , , Giornale Botanico Italiano, 1844

5.
A revision of the ''Endogonaceae'', Thaxter, R., , , Proc. Am. Acad. Arts Sci., 1922

6.
The ''Endogonaceae'' in the Pacific Northwest, J.W. Gerdemann & J.M. Trappe, , , Mycologia Memoirs, 1974

7. Revised classification of arbuscular mycorrhizal fungi (''Zygomycetes''): a new order, ''Glomales'', two new suborders, ''Glomineae'' and ''Gigasporineae'', and two new families, ''Acaulosporaceae'' and ''Gigasporaceae'', with an emendation of ''Glomaceae'', J.B. Morton & G.L. Benny, , , Mycotaxon, 1990

8.
Microbial Endophyes, Morton, J.B., , , Marcel Dekker, 2000,
9.
Analysis of partial ''Glomales'' SSU rRNA gene sequences: implications for primer design and phylogeny, Schüßler, A. ''et al.'', , , Mycol. Res., 2001

10. Molecular identification and phylogeny of arbuscular mycorrhizal fungi, Redeker, D., , , Plant and Soil, 2002
11.
Systematics and taxonomy of the arbuscular mycorrhizal fungi (''Glomales'') - a possible way forward, Walker, C., , , Agronomie, 1992

12.
Specific Amplification of 18S Fungal Ribosomal Genes from Vesicular-Arbuscular Endomycorrhizal Fungi Colonizing Roots, Simon, L. Lalonde, M. Bruns, T.D., , , American Society of Microbiology, 1992

13. Ecological and evolutionary significance of mycorrhizal symbiosis in vascular plants (a review), D.W. Malloch, K.A. Pirozynski & P.H. Raven, , , Proc. Natl Acad. Sci. USA, 1980

External links

★ Glomeromycota at the Tree of Life Web Project

★ Glomeromycota at the International Culture Collection of VA Mycorrhizal Fungi (INVAM)

★ Glomeromycota at the University of Sydney Fungal Biology s|ite

★ 'AMF-phylogeny' - web-site at the University of Darmstadt