Rhizophagus irregularis DAOM 181602 v1.0
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Glomus intraradices
Glomus intraradices arbuscules. Photo credit: Y. Piché.

Within the framework of the JGI Mycorrhizal Genomics Initiative, we are sequencing a phylogenetically and ecologically diverse suite of mycorrhizal fungi (Glomeromycota, Basidiomycota and Ascomycotina), which include the major clades of symbiotic species associating with plants. Analyses of these genomes will provide insight into the diversity of mechanisms for the mycorrhizal symbiosis, including arbuscular-, ericoid, orchid-, and ecto-mycorrhizal symbioses.

 

The arbuscular mycorrhizal (AM) symbiosis between fungi in the Glomeromycota and plants involves over two-thirds of all known plant species, including important crop species, such as wheat, rice, maize, soybean and poplar. This mutualistic symbiosis, involving one of the oldest fungal lineages, is arguably the most ecologically and agriculturally important symbiosis in terrestrial ecosystems. The molecular basis of this life-style, obligate biotrophy, remains unknown. To provide novel insights into the molecular basis of symbiosis-associated traits, we report the sequencing, assembly and annotation of the nuclear genome from Rhizophagus irregularis (Glomeromycota, Glomeromycetes, Glomerales, Glomeraceae). The sequenced strain DAOM 197198 was formerly known as Glomus intraradices.

 

The Glomeromycota are unique in that their spores and coenocytic hyphae contain multiple nuclei in a common cytoplasm. No sexual cycle is known, although anastomosis and nuclear movement between hyphae of the same species have been described.

 

Several factors have led to the choice of R. irregularis for the first genome sequencing of an AM fungus. As a symbiont, R. irregularis is highly effective in mobilizing, taking up and transferring mineral nutrients, such as inorganic orthophosphate ions (Pi), N and sulfur (S), from soils to plants and it readily colonizes many plants, including agriculturally important crop species as well as model plants such as Medicago truncatula, Lotus japonicus and Populus trichocarpa. R. irregularis is one of the most studied AM fungi as it rapidly colonizes its host plants, and it is a model species for dissecting the molecular and cellular biology of the Glomeromycota. It is readily amenable to in vitro culture on transformed host roots and is the only species for which spores are available commercially in pure form in large quantities.

 

The comparative analyses of gene repertoires in R. irregularis, pathogenic obligate biotrophs and ectomycorrhizal fungi offer insights into genes that may be involved in obligate biotrophy and mycorrhizal symbioses

 

The present R. irregularis genome, the first for Glomeromycota, provides a basis for future research in environmental genomics and for accessing symbiosis-related functional features in other members of this unique phylum.

Genome Reference(s)