''Glomus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

arbuscular mycorrhiza An arbuscular mycorrhiza (AM) (plural ''mycorrhizae'', a.k.a. ''endomycorrhiza'') is a type of mycorrhiza in which the symbiont fungus (''AM fungi'', or AMF) penetrates the cortical cells of the roots of a vascular plant forming arbuscules. (N ...

l (AM)

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

, and all

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

form

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

relationships (

mycorrhiza A mycorrhiza (from Greek μύκης ', "fungus", and ῥίζα ', "root"; pl. mycorrhizae, mycorrhiza or mycorrhizas) is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in the plant ...

e) with plant

root In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the sur ...

s. ''Glomus'' is the largest genus of AM fungi, with ''ca.'' 85 species described, but is currently defined as non-

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

Classification

''Glomus'' is one of the genera in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Glomeraceae, in the

division Division or divider may refer to: Mathematics *Division (mathematics), the inverse of multiplication *Division algorithm, a method for computing the result of mathematical division Military *Division (military), a formation typically consisting ...

Glomeromycota Glomeromycota (often referred to as glomeromycetes, as they include only one class, Glomeromycetes) are one of eight currently recognized divisions within the kingdom Fungi, with approximately 230 described species. Members of the Glomeromycot ...

. Some members of the genus were originally described as ''Sclerocystis'' species, but this genus has been entirely transferred to ''Glomus''. However, further taxonomic changes are likely as the phylogeny of AM fungi becomes better understood. ''Glomus'' is likely related to the fossil fungus '' Glomites'', discovered in the

Rhynie chert The Rhynie chert is a Lower Devonian sedimentary deposit exhibiting extraordinary fossil detail or completeness (a Lagerstätte). It is exposed near the village of Rhynie, Aberdeenshire, Scotland; a second unit, the Windyfield chert, is locate ...

deposits from the

Early Devonian The Early Devonian is the first of three Epoch (geology), epochs comprising the Devonian period, corresponding to the Lower Devonian Series (stratigraphy), series. It lasted from and began with the Lochkovian Stage , which was followed by the P ...

(400 million years ago).

Ecology

As with other AM fungi, all ''Glomus'' species are thought to be

obligate symbiont Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

s, dependent on their mycorrhizal association with plant roots to complete their

life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the production of the offspring * Life-cycle hypothesis ...

. They cannot be cultured in the laboratory in the absence of a plant host. ''Glomus'' species are found in nearly all

terrestrial Terrestrial refers to things related to land or the planet Earth. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on or near the ground, as opposed to ...

habitats, including

arable land Arable land (from the la, arabilis, "able to be ploughed") is any land capable of being ploughed and used to grow crops.''Oxford English Dictionary'', "arable, ''adj''. and ''n.''" Oxford University Press (Oxford), 2013. Alternatively, for the ...

desert A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About on ...

grassland A grassland is an area where the vegetation is dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur natur ...

tropical forest Tropical forests (a.k.a. jungle) are forested landscapes in tropical regions: ''i.e.'' land areas approximately bounded by the tropic of Cancer and Capricorn, but possibly affected by other factors such as prevailing winds. Some tropical fores ...

s, and

tundra In physical geography, tundra () is a type of biome where tree growth is hindered by frigid temperatures and short growing seasons. The term ''tundra'' comes through Russian (') from the Kildin Sámi word (') meaning "uplands", "treeless moun ...

s. Arbuscular mycorrhizal fungi can provide numerous benefits to their plant hosts, including improved nutrient uptake,

drought resistance Drought tolerance is the ability to which a plant maintains its biomass production during arid or drought conditions. Some plants are naturally adapted to dry conditions'','' surviving with protection mechanisms such as desiccation tolerance, detox ...

, and disease resistance. However, the symbiosis is not mutualistic in all circumstances and may often be

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...

, with a detrimental effect on plant growth. Rarely, some plant species can parasitise the fungi. Spores of ''Glomus'' prior to germinating produce an electric current.

Life cycle

''Glomus'' species were considered to be entirely asexual until recently (see Meiosis section below). Spores are produced at the tips of

hyphae A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

either within the host root or outside the root in the

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...

. Thought to be chlamydospores, these spores germinate and the germination tube that is produced grows through the soil until it comes into contact with roots. The fungus then penetrates the root and grows between root cells, or it may penetrate the

cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mech ...

and grow within root cells. Inside the root, the fungus forms arbuscules, which are highly branched hyphal structures that serve as sites of nutrient exchange with the plant. Arbuscules are formed within plant cell walls but are surrounded by an invaginated

cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...

, so remain within the

apoplast Inside a plant, the apoplast can mean the space outside of cell membranes, where material can diffuse freely; that is, the extracellular spaces. ''Apoplast '' can also refer especially to the continuum of cell walls of adjacent cells; fluid and ...

. The fungus may also form vesicles, swollen structures which are thought to function as food storage organs.

Meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...

Halary et al. searched the genomes of four ''Glomus'' species for the presence of genes that encode proteins essential for

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...

. These proteins make up the conserved meiotic recombination machinery of

eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

cells. The study indicated that the ''Glomus'' species contain 51 genes encoding all the tools necessary for meiotic recombination and associated

DNA repair DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA dam ...

processes. In particular, these species have seven genes that encode proteins whose only known function is in meiosis, including ''

Dmc1 Meiotic recombination protein DMC1/LIM15 homolog is a protein that in humans is encoded by the ''DMC1'' gene. Meiotic recombination protein Dmc1 is a homolog of the bacterial strand exchange protein RecA. Dmc1 plays the central role in homologous ...

'' that is a meiosis-specific recombinase. Since meiosis is considered to be a hallmark of

sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

, it might be expected that a sexual stage or a sexual apparatus should be present. However, as yet, none has been identified. In addition,

mating type Mating types are the microorganism equivalent to sexes in multicellular lifeforms and are thought to be the ancestor to distinct Sex, sexes. They also occur in macro-organisms such as fungi. Definition Mating types are the microorganism equivalent ...

gene homologues and a putative sex hormone-sensing pathway were detected in these fungi. Based on these findings it was suggested that Glomus species may be able to undergo a cryptic sexual cycle. The population structure of ''Glomus etunicatum'' suggests that clonal expansion plays an important role in the ecological success of ''Glomus'' species, and that gene exchanges are not completely absent, although likely very rare.

Agricultural significance

Several species of ''Glomus'', including '' G. aggregatum'', are cultured and sold as mycorrhizal

inoculant Inoculation is the act of implanting a pathogen or other microorganism. It may refer to methods of artificially inducing immunity against various infectious diseases, or it may be used to describe the spreading of disease, as in "self-inoculati ...

for agricultural soils. One species, ''G. macrocarpum'' (and possibly also ''G. microcarpum''), causes

tobacco Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...

stunt disease.

Species

* ''

Glomus aggregatum ''Glomus aggregatum'' is an arbuscular mycorrhizal fungus used as a soil inoculant in agriculture and horticulture. Like other species in this phylum it forms obligate symbioses with plant roots, where it obtains carbon (photosynthate) from the h ...

'' * '' Glomus albidum'' * '' Glomus ambisporum'' * '' Glomus brazillanum'' * '' Glomus caledonium'' * '' Glomus coremioides'' * '' Glomus claroideum'' * '' Glomus clarum'' * '' Glomus clavisporum'' * '' Glomus constrictum'' * '' Glomus coronatum'' * '' Glomus deserticola'' * '' Glomus diaphanum'' * '' Glomus eburneum'' * '' Glomus etunicatum'' * '' Glomus fasciculatum'' * '' Glomus fistulosum'' * '' Glomus fragilistratum'' * '' Glomus geosporum'' * '' Glomus globiferum'' * '' Glomus heterosporum'' * '' Glomus hoi'' * ''

Glomus intraradices ''Rhizophagus irregularis'' (previously known as ''Glomus intraradices'') is an arbuscular mycorrhizal fungus used as a soil inoculant in agriculture and horticulture. ''Rhizophagus irregularis'' is also commonly used in scientific studies of the ...

'' * '' Glomus lacteum'' * '' Glomus lamellosum'' * '' Glomus luteum'' * '' Glomus manihotis'' * '' Glomus microaggregatum'' * '' Glomus monosporum'' * '' Glomus mosseae'' * '' Glomus multicaule'' * '' Glomus pansihalos'' * '' Glomus pustulatum'' * '' Glomus sinuosum'' * '' Glomus spurcum'' * '' Glomus tortuosum'' * '' Glomus trimurales'' * '' Glomus verruculosum'' * '' Glomus versiforme'' * '' Glomus viscosum''

References

"Genus ''Glomus''" at the Catalogue of Life Checklist

* ttps://web.archive.org/web/20070313001714/http://www.biologie.uni-hamburg.de/b-online/library/steur/engrhyn/eglomit.html Symbiotic Fungi {{Authority control Glomerales Fungus genera Taxa named by Edmond Tulasne