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Meliniomyces bicolor
A. 6-weeks old colony of Meliniomyces bicolor strain E on potato dextrose agar. Photo credit: David Riley. B. 12-months old symbiosis between host Pinus sylvestris and fungus Meliniomyces bicolor strain B. The symbiosis was grown on agar media in gnobiotic condition. Photo credit: Gwen Grelet. C. 8-months old symbiosis between host Vaccinium myrtillus and fungus Meliniomyces bicolor strain E. The symbiosis was grown in axenic conditions in peat-vermiculite medium. The right-end side compartment contains agar and nutrients and is accessible to fungal hyphae only (not roots). This set up was used to demonstrate that carbon was transferred from plant shoot to fungal hyphae, and that nitrogen was translocated from hyphae growing in the agar compartment to the Vaccinium shoot. Photo credit: David Riley.

Within the framework of the JGI Mycorrhizal Genomics Initiative, we are sequencing a phylogenetically and ecologically diverse suite of mycorrhizal fungi (Basidiomycota and Ascomycota), which include the major clades of symbiotic species associating with trees and woody shrubs. Analyses of these genomes will provide insight into the diversity of mechanisms for the mycorrhizal symbiosis, including ericoid-, orchid- and ectomycorrhizal associations.

Meliniomyces bicolor

Meliniomyces bicolor Hambleton & Sigler belongs to the phylum Ascomycota, class Leotiomycetes and order Helotiales. M. bicolor is part of the Rhizoscyphus ericae aggregate (Vrålstad et al. 2000), a species complex comprising of at least 4 other root-associated fungal taxa, including Meliniomyces variabilis, Rhizoscyphus ericae and Cadophora finlandica (Hambleton & Sigler, 2005).

Meliniomyces bicolor ,and the closely related Cadophora finlandica (Wang & Wilcox), colonise the roots of many Northern temperate forest trees, such as pine, spruce and birch. Both form on pine roots the well-defined and characteristic ectomycorrhizal morphotype Piceirhiza bicolorata (Agerer, R.; 1987). However, In Northern temperate and boreal forests, M. bicolor can also form ericoid mycorrhiza with understory shrubs in the Ericaceae family such as Vaccinium spp. In fact, M. bicolor was shown to behave like a typical ericoid mycorrhizal fungus in vitro, inducing significantly higher growth rate in its ericaceous host compared to non-infected seedlings, and engaging in measurable reciprocal transfer of carbon and nitrogen (Grelet et al., 2009).

Meliniomyces bicolor strain E was isolated in the fall of 2005, from a typical Piceirhiza bicolorata ectomycorrhizal root tip collected in the native Caledonian pine forest of Glen Tanar (North East Scotland, 57.01 N, 2.52 W). It is slow growing and produces highly melanised filamentous hyphae (fig. A). This strain can readily colonise and form typical P. bicolorata ectomycorrhiza with Betual pendula and Pinus sylvestris seedlings in laboratory conditions (fig. B) as well as typical ericoid mycorrhiza with axenically grown seedlings of Vaccinium myrtillus and V. Vitis-idaea (fig. C).

The genetic mechanisms underlying the dual mycorrhizal ability of Meliniomyces bicolor are unknown. Its ability to form such contrasted infection structures, involving both extracellular and intracellular defined growth patterns, is puzzling. Deciphering its genome will allow us to make considerable advances in our understanding of the genetic and functional basis of mutualistic plant-fungi interactions, and will contribute substantially to the on-going genomes comparison of a diverse suite of mycorrhizal fungi and fungal wood decayers.

Genome Reference(s)

  • Grelet GA. et al. 2009. Reciprocal carbon and nitrogen transfer between an ericaceous dwarf shrub and fungi isolated from Piceirhiza bicolorata ectomycorrhizas. New Phytologist 182(2): 359-366.
  • Agerer (1987). Color Atlas of Ectomycorrhizae. Einhorn Verlag, Schwabisch Gmund Pi.
  • Hambleton S. & Sigler L. 2005. Meliniomyces, a new anamorph genus for root-associated fungi with phylogenetic affinities to Rhizoscyphus ericae ( Hymenoscyphus ericae), Leotiomycetes. Studies in Mycology 53: 1-27.
  • Vralstad T et al. (2000). Piceirhiza bicolorata - the ectomycorrhizal expression of the Hymenoscyphus ericae aggregate? New Phytologist 145: 549-563.