Ectomycorrhizal Influence on the Dynamics of Sesquiterpene Release by Tricholoma vaccinum

Tricholoma vaccinum is an ectomycorrhizal basidiomycete with high host specificity. The slow-growing fungus is able to produce twenty sesquiterpenes, including α-barbatene, sativene, isocaryophyllene, α-cuprenene, β-cedrene, ß-copaene, 4-epi-α-acoradiene, and chamigrene in axenic culture. For the three major compounds, Δ 6 -protoilludene, β-barbatene, and an unidentified oxygenated sesquiterpene ( m/z 218.18), changed production during co-cultivation with the ectomycorrhizal partner tree, Picea abies , could be shown with distinct dynamics. During the mycorrhizal growth of T. vaccinum – P. abies , Δ 6 -protoilludene and the oxygenated sesquiterpene appeared at similar times, which warranted further studies of potential biosynthesis genes. In silico analyses identified a putative protoilludene synthesis gene, pie1 , as being up-regulated in the mycorrhizal stage, in addition to the previously identified, co-regulated geosmin synthase, ges1 . We therefore hypothesize that the sesquiterpene synthase pie1 has an important role during mycorrhization, through Δ 6 -protoilludene and/or its accompanied oxygenated sesquiterpene production.