Fruiting bodies of the oak milkcap (Lactarius quietus). Note the white milk-like liquid exuding from the broken cap. Credit: Francis Martin, INRA.

Within the framework of the Mycorrhizal Genomics Initiative (MGI) and the 1000 Fungal Genomes (1KFG) project, we are aiming to explore the interaction of forest trees with communities of soil fungi, including ectomycorrhizal symbionts that dramatically affect tree growth, and saprotrophic soil fungi impacting carbon cycling in forests. These fungal genomes are compared to understand the evolution of nutrition modes in Fungi. In addition, genomes of species harvested on long-term observatories are providing sufficient taxonomic coverage of fungal genomes to identify and analyze DNA and RNA samples sequenced from environmental samples.

The Oak Milkcap, Lactarius quietus - An Oak-specific Symbiont
The Lactarius genus in the Russulales order is one of the larger known genera of ectomycorrhiza-forming basidiomycetes. Lactarius quietus produces solitarily or scattered groups of fleshy reddish brown fruiting body specifically under oak. The presence of lactiferous hyphae in the fruiting body and ectomycorrhizas is visible through latex exudation from cut or broken tissue in fresh material. In Europe, field observations indicate that a relatively high degree of host specificity exists for most species of Lactarius and L. quietus commonly forms ectomycorrhiza with Quercus species. In North America, the subspecies L. quietus var. incanus is fairly common in the same habitat.

The sequenced diploid isolate S23C was isolated from an ectomycorrhizal root tip collected in a 100-year-old oak French forest in Lorraine by Dr. P-E Courty. Several laboratories investigating the population genetics of this ectomycorrhizal symbiotic fungus will benefit from genetic markers and protein-coding genes to study Lactarius populations. Moreover, L. quietus is an excellent model for studying fungus-host interactions, because of the relatively high degree of host specificity for most species of Lactarius, including L. quietus.

As always, please contact the MGI PI (Francis Martin, INRA) associated with unpublished genomes for permission prior to the use of any data in publications.