Glomeromycota — Overview

Arbuscular Mycorrhizal Fungi and Their Relatives learn more about names for this taxon

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The fungi phylum Glomeromycota is essentially unknown by the general public, however behind the scenes these taxa are ubiquitous, one of the most widespread and most important (economically and ecologically) fungal group, despite the small number of species it includes (about 150).  Although many species are not known biologically, all glomeromycotan species are believed to form obligate symbiotic relationships with phototrophs.  Most of these relationships occur (in an enormous diversity of plant species) via formation of “arbuscular mycorrhizal” (AM) associations within the roots, which allow the fungi to use carbohydrates produced by the plant.  In exchange the fungi dramatically increase mineral uptake (phosphorus, in particular) for the plant, essentially extending the plants’ root network with a vast mycorrhiza network. 

Glomeromycotan fungi appear to have low host specificity and a plant might be colonized by multiple species of glomeromycotan species, furthermore, the fungi themselves may form complex underground webs, even indirectly connecting the roots of different species of plants.  Glomeromycota are recorded to significantly impact the growth of most herbaceous plants and tropical trees including almost all human food crops, influence the composition of plant species in plant communities, control pests and fungal pathogens, and ameliorate effects of pollution on plant fitness.  These fungi may be fundamental in sustainable agriculture practices to solve the problem of rapidly depleting rock phosphate reserves, and are relevant to global warming as a significant CO2 sink, receiving and holding fixed carbon in the soil. 

Only very few plants (including less than 20% of existing vascular plants) are known to not form these AM relationships with glomeromycotans.  Some of these are plants in families Brassicaceae (e.g. cabbage, Arabidopsis), Caryophyllaceae (e.g. carnation) and Chenopodiaceae (e.g. spinach).  A small number of glomeromycotan species form other kinds of symbioses, some form external (ectomycorrhizal) associations with trees and shrubs, some form mycorrhizal associations with Asco- or Basidiomycota fungi.  One glomeromycotan (Geosiphon pyriformis), thought to be a primitive representative of the group, forms a symbiosis with cyanobacteria, in which they are the macrosymbiont, housing a consortium of the cyanobacteria in specialized bladders; a relationship possibly representing an ancestral type of symbiosis evolving before terrestrial plant life.   

The Glomeromycota are the oldest known fungi group, found in Ordovician fossils from 460 million years ago, and are hypothesized to have originated 600 million years ago, before the divergence of Asco- Basidiomycota fungi.  Scientists hypothesize these fungi had an important role in the process of early (rootless) land plants colonizing terrestrial habitats. 

The phylum Glomeromycota was created in 2001 as the smallest of the seven currently recognized fungi phyla, representing a very recent understanding of this group.  As late as 1974, glomeromycotan species were all placed in genus Endogone within Zygomycota.  Beginning in the early 2000’s molecular studies uncovered far more diversity at species-, genus- and family-level than traditional morphological characterizations documented (primarily as spore morphologies).  Glomeromycota currently is considered to contain between 150-200 “morphospecies,” however this may well be an underestimate.  Nice descriptions of diversity and evolution of this group can be explored at the Schüßler lab web site

(Redecker and Raab 2006; Redecker 2008; Schüßler, Schwarzott and Walker 2001; Wikipedia 2014a, b)

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