Glomeromycota

Taxobox
name = Glomeromycota
regnum = Fungi
phylum = Glomeromycota
phylum_authority = C. Walker & A. Schuessler 2001cite journal | author = Schüßler, A. "et al." |month=Dec| year=2001 | title=A new fungal phlyum, the "Glomeromycota": phylogeny and evolution. | journal=Mycol. Res. | volume=105 | issue=12 | pages=1413–1421 | url=http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=95091 | doi=10.1017/S0953756201005196]
classis = Glomeromycetes
classis_authority = Caval.-Sm., 1998 [cite journal | author=Cavalier-Smith, T. | year = 1998 | title = A revised six-kingdom system of Life | journal = Biol. Rev. Camb. Philos. Soc. | volume = 73 | pages = 246 (as "Glomomycetes")]
subdivision_ranks = Orders
subdivision =
Glomerales
Diversisporales
Paraglomerales
Archaeosporales

Glomeromycota (informally glomeromycetes) is one of seven currently recognized phyla within the kingdom Fungicite journal
author=Hibbett, D.S., "et al."
month=Mar
year=2007
title=A higher level phylogenetic classification of the "Fungi"
journal=Mycol. Res.
volume=111
issue=5
pages=509–547
doi=10.1016/j.mycres.2007.03.004] , with approximately 200 described species. [ [http://www.lrz-muenchen.de/~schuessler/amphylo/amphylogeny.html Neue Seite 1 ] ] Members of the Glomeromycota form arbuscular mycorrhizas with the roots or thalli (e.g. in bryophytes) of land plants. "Geosiphon pyriformis" forms an endocytobiotic association with "Nostoc" cyanobacteria [ [http://www.lrz-muenchen.de/~schuessler/geosiphon/geosiphon.html New Page 1 ] ] . 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 [cite journal
author=Hempel, S., Renker, C. & Buscot, F.
year=2007
title=Differences in the species composition of arbuscular mycorrhizal fungi in spore, root and soil communities in a grassland ecosystem
journal=Environmental Microbiology
volume=9
issue=8
pages=1930–1938
doi=10.1111/j.1462-2920.2007.01309.x] . 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.

Reproduction

The Glomeromycota have generally coenocytic (occasionally sparsely septate) mycelia and reproduce asexually through blastic development of the hyphal tip to produce spores (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. [cite journal
author=Tulasne, L.R., & C. Tulasne
year=1844
title=Fungi nonnulli hipogaei, novi v. minus cogniti auct | journal=Giornale Botanico Italiano
volume=2
pages=55–63] 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. [cite journal
author=Thaxter, R.
year=1922
title=A revision of the Endogonaceae
journal=Proc. Am. Acad. Arts Sci.
volume=57
pages=291–341] Following broader reviews that cleared up the sporocarp confusion, the Glomeromycota were first proposed in the genera "Acaulospora" and "Gigaspora" [cite journal
author=J.W. Gerdemann & J.M. Trappe
year=1974
title=The Endogonaceae in the Pacific Northwest
journal=Mycologia Memoirs
volume=5
pages=1–76] before being accorded their own order with the three families Glomaceae (now Glomeraceae), Acaulosporaceae and Gigasporaceae. [cite journal
author=J.B. Morton & G.L. Benny
year=1990
url=http://www.cybertruffle.org.uk/cyberliber/59575/0037/0471.htm
title=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
journal=Mycotaxon
volume=37
pages=471–491]

With the advent of molecular techniques this classification has undergone major revision. An analysis of small subunit (SSU) rRNA sequences [cite journal
author = Schüßler, A. "et al."
month=Jan
year=2001
title=Analysis of partial Glomales SSU rRNA gene sequences: implications for primer design and phylogeny
journal=Mycol. Res.
volume=105
issue=1
pages=5–15
doi=10.1017/S0953756200003725] 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 [cite journal|author=Redeker, D.|year= 2002|title= Molecular identification and phylogeny of arbuscular mycorrhizal fungi|journal= Plant and Soil|volume= 244|pages=67–73|doi= 10.1023/A:1020283832275] 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"cite journal|author=Schüßler, A.|year= 2002|title= Molecular phylogeny, taxonomy, and evolution of "Geosiphon pyriformis" and arbuscular mycorrhizal fungi|journal= Plant and Soil|volume= 224 |pages=75–83|doi= 10.1023/A:1020238728910] 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 [cite journal
author = Walker, C.
year = 1992
title = Systematics and taxonomy of the arbuscular mycorrhizal fungi (Glomales) - a possible way forward
journal = Agronomie
volume = 12
pages = 887–897
doi = 10.1051/agro:19921026] or families.cite journal
author=Simon, L., Bousquet, J., Levesque, C., Lalonde, M.
year= 1993
title= Origin and diversification of endomycorrhizal fungi and coincidence with vascular land plants
journal= Nature
volume= 363
issue=6424
pages= 67–69
doi= 10.1038/363067a0]

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). [cite journal
author=Simon, L. Lalonde, M. Bruns, T.D.
year= 1992
title= Specific Amplification of 18S Fungal Ribosomal Genes from Vesicular-Arbuscular Endomycorrhizal Fungi Colonizing Roots
journal= American Society of Microbiology
volume= 58
pages= 291–295] 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. [cite journal
author=D.W. Malloch, K.A. Pirozynski & P.H. Raven
year=1980
title=Ecological and evolutionary significance of mycorrhizal symbiosis in vascular plants (a review)
journal=Proc. Natl Acad. Sci. USA
volume=77
issue=4
pages=2113–2118
url=http://www.pnas.org/cgi/content/short/77/4/2113
doi=10.1073/pnas.77.4.2113
pmid=16592806]

See also

References

External links

* [http://tolweb.org/Glomeromycota/28715 Tree of Life Glomeromycota]
* [http://invam.caf.wvu.edu/fungi/taxonomy/glomales.htm Glomeromycota] at the International Culture Collection of VA Mycorrhizal Fungi (INVAM)
* [http://bugs.bio.usyd.edu.au/Mycology/Taxonomy/glomeromycota.shtml Glomeromycota] at the University of Sydney Fungal Biology s|ite
* [http://amf-phylogeny.com 'AMF-phylogeny'] - 'Glomeromycota database' web-site at the University of Munich