Ectomycorrhizal fungi colonize the dominant tree species in boreal, temperate and tropical forests where they play a key role in nutrient cycling and carbon sequestration. They are not a phylogenetically distinct group, but they are all part of the Dikarya. There is thus a major interest into how this lifestyle developed in such a wide variety of fungi and how this change was effected.
The Basidiomycete Agaric Hebeloma cylindrosporum Romagnesi (Cortinariaceae) has only been reported to occur in Europe, from Finland or Norway in the north to Spain in the south. It is frequently found in forest stands developing on sand dunes with very little organic matter along the atlantic or mediterranean coast. In this respect, H. cylindrosporum can be qualified as a pioneer species which thrives in newly established forests or in disturbed areas. H. cylindrosporum is frequently associated with different pine trees such as Pinus pinaster. It can also form mycorrhizas with additional hosts which do not occur in its natural habitats. The most remarkable feature of H. cylindrosporum as an ectomycorrhizal fungal species is that its entire life cycle, including fruit body formation, can be obtained under axenic conditions in the laboratory using defined culture media. It can be routinely transformed using Agrobacterium tumefaciens and insertional mutant libraries are available making it possible reverse genetic approach to identify fungal functions essential for symbiosis establishment. In addition, the genomic sequence of C. puteana will contribute to a better prospect of brown rot as a fungal nutritional mode, which apparently harbors more than only one ecological strategy.
The on-going sequencing of a phylogenetically and ecologically diverse suite of mycorrhizal fungi, which includes H. cylindroposrum, together with the major clades of symbiotic species associating with trees and woody shrubs will provide insight into the diversity of mechanisms for the mycorrhizal symbiosis. In concert with the sequencing of a suite of fungal wood decayers, these mycorrhizal genomes will also illuminate the functional basis of transitions between decayer and mutualist lifestyles.
Reference: Marmeisse R, Guidot A, Gay G, Lambilliotte R, Sentenac H, Combier JP, Melayah D, Fraissinet-Tachet L, Debaud JC (2004) Hebeloma cylindrosporum - a model species to study ectomycorrhizal symbiosis from gene to ecosystem. New Phytologist 163, 481-498.