Glomus

Classification

Eukaryota; Fungi/Metazoa group; Fungi; Glomermycota; Glomermycetes; Glomerales; Glomeraceae(http://www.ncbi.nlm.nih.gov/Taxonomy/ NCBI)

Species

Glomus aggregatum;Glomus aurantium;Glomus aureum;Glomus badium;Glomus caledonium;Glomus claroideum;Glomus cf. claroideum;Glomus clarum;Glomus cf. clarum;Glomus constrictum;Glomus coremioides;Glomus coronatum;Glomus deserticola;Glomus diaphanum;Glomus cf. diaphanum 589;Glomus dimorphicum;Glomus drummondi;Glomus eburneum;Glomus cf. eburneum;Glomus etunicatum; Glomus cf. etunicatum W2423; Glomus fasciculatum; Glomus fragilistratum; Glomus fulvum; Glomus geosporum; Glomus cf. geosporum W2538; Glomus heterosporum; Glomus hoi; Glomus hyderabadensis; Glomus intraradices; Glomus intraradices DAOM 197198; Glomus cf. intraradices; Glomus irregulare; Glomus lamellosum; Glomus luteum; Glomus macrocarpum; Glomus manihotis; Glomus megalocarpum; Glomus microaggregatum; Glomus cf. microaggregatum; Glomus monosporum; Glomus mosseae;Glomus proliferum; Glomus pulvinatum; Glomus sinuosum; Glomus cf. sinuosum; Glomus trimurales; Glomus verruculosum; Glomus versiforme; Glomus vesiculiferum; Glomus viscosum; Glomus walkeri; Glomus xanthium

Description and Significance

Glomus exist in the environment both as a spore and hyphae which can form dense networks called mycelium, though most of Glomus biomass occurs within roots of host plants. Spores are typically borne on the terminal end of hyphae and generally spherical in appearance. Hyphae have filamentous appearance, but can be seen with the eye when a mycelium is formed, a dusty appearance on the mycelium indicate the presence of spores Mycelium are the result of substrate exploration by individual hyphae. Glomus exists in all terrestrial habitats. Plant and soil transplant experiments have found Glomus species that exhibit both r and K strategies (e.g. G. mosseae and G. badium, respectiviely) ( Sykorova et al 2007). As an endosymbiotic organism Glomus may inhabitat the roots of 70-90% of vascular plants. It is important ecologically by providing nutrients to it host. Arbusculars are formed within the cell wall that have the appearance of small trees or bushes Phosphorous, nitrogen and water may be provided to host plants through the intracellular interface (Schubler 2001). Infection of roots with Glomus may also protect the host plant from harmful soil borne pathogens. These attributes of the Glomus-plant symbiosis play an important role in the economic sectors involving the growth of plants such as agriculture, horticulture and forestry.

Genome Structure

At this point in time the compleate Glomus genome is not available. Several possible reasons for why the genome is not assembling completely are as follows; there are a high amount of multiple copies of nuclear genes, the genomes larger physical size, cloning bias, the substantial amounts of undetected contamination, and polymorphism. (Shapiro, 2008). What we do know about the Glomus genome. There are at least four chromosomes in Glomus intraradices but there are probably more. The minimal number of chromosomes was found by cloning and sequencing the highly divergent telomere-associated sequences (TAS) and by pulsed field gel electrophoresis (PFGE). (Mohamed Hijria, b, Hélène Niculitaa and Ian R. Sandersa 2007). Reassociation kinetics on Glomus intraradices DNA indicated a haploid genome size of ~16.54 Mb, comprising 88.36% single copy DNA, 1.59% repetitive DNA, and 10.05% fold-back DNA. (Mohamed Hijria, b, Hélène Niculitaa and Ian R. Sandersa 2007). By looking at the genetic make-up of AM fungi it is likely that Glomus is related to fossil fungi that have existed for over 400 million years qualifying it as a living fossil.

Cell Structure, Metabolism and Life Cycle

Glomus is an obligate biotroph, meaning it requires a living photoautotropic host for it to be able to compleate their life cycle and produce the next generation of spores. Glomus species are also entirely asexual. (Modjo, H.S., Hendrix, J.W. 1986) Glomus begins as a spore, the spores can be produce either inside the host roots or outside in the soil. Glomus spores are able to germinate without a host plant. These spores are produced at the end of the hyphae. Once produced the spores germinates. If the spore is not already in the root a germination tube is formed which grows through the soil until it finds a root to make its host. The Glomus penetrates in one of two spots. Either it penetrates the root and grows between root cells or it penetrates the cell wall and grows within root cells. Once Glomus penetrates the root cells arbuscules are formed. The arbuscules are tree-shaped subcellular structures that form to connect plants to the hyphal network of the fungi. Arbuscules are the main site for nutrient exchange between Glomus and its symbiotic plant partners. Soil may contain over 100 meters of hyphae per cubic centimeter. (Parniske 2008) This network of hyphae is designed to increase the plants uptake of important nutrients such as phosphates and water. In exchange for the nutrients and water the plants supply Glomus with the carbohydrates it needs to survive.

Ecology and Pathogenesis

Glomus is not known to be pathogenic. As a fungi, Glomus, contributes to fungal biomass dominance of soils. Glomus is an arbuscular mycorrhiza, or endomychorizza, meaning it penetrates the cell wall of it host plant. Within the cell wall the fungi forms arbusuclars or tree like structures at the subcellular level. Arbuscular are the site of transfer of materials between host and fungi. Glomus, like all AM, are obligate heterotrophs, that is they require a host to obtain organic nutrients (Schubler et al 2001). In return the host plant acquires inorganic nutrients from the AM fungi. In this respect, Glomus can an important role in the overall nutrient cycling of ecosystems. Estimates of host plant organic input to AM species range from 1 to 20%. Host specificity in AM has led to a link a positive correlation in AM diversity and plant diversity, they may protect plant roots from pests, and increase overall fitness of their host.

References

Modjo, H.S., Hendrix, J.W. (1986) The mycorrhizal fungus "Glomus macrocarpum" as a cause of tobacco stunt disease. Phytopathology. Vol 76. pp 688–691.

Mohamed Hijria, b, Hélène Niculitaa and Ian R. Sandersa. Molecular characterization of chromosome termini of the arbuscular mycorrhizal fungus Glomus intraradices (Glomeromycota). Fungal Genetics and Biology Volume 44, Issue 12, December 2007, Pages 1380-1386

Parniske, Martin. Arbuscular mycorrhiza: the mother of plant root endosymbioses. Nature Reviews Microbiology 6, 763-775 October 2008

Schubler, A., Schawrzott, D., and Walker, C. 2001 "A new phylum, the Glomermycota: phylogeny and evolution." Mycol. Res. 105 (12) p. 1413-1421

Shapiro, Harris. Glomus intraradices: Status of the Genome Pro ject. Lawrence Berkeley National Laboratory. Paper LBNL 1109E, 2008

Sykorova, Z., Ineichen, K., Wiemken, A., Redecker, D. 2007 "The cultivation bias: different communities of arbuscular mycorrhizal fungi detected in roots from the feild, from bait plants transplanted to the field, and from a greenhouse trap experiment." Mycorrhiza 18: 1-14

[==Author== Page authored by _Ryan Colliton and Aaron Cooch, student of Prof. Jay Lennon at Michigan State University.