Terpenoid biosynthesis in the cultivated mushroom Cyclocybe aegerita

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Terpenoids constitute a structurally diverse group of natural products with indispensable applications in the pharmaceutical, nutritional, flavour and fragrance industries. Fungi of the phylum Basidiomycota are known to produce a large variety of terpenoids, yet their biosynthesis pathways remain largely unexplored. The genome of the mushroom model system Cyclocybe aegerita (syn. Agrocybe aegerita) contains nine functional sesquiterpene synthases (STS), of which four are part of biosynthetic gene clusters. By the heterologous expression of these clusters in the related model agaric fungus Coprinopsis cinerea, the peculiar characteristics of these biosynthesis pathways will be investigated in detail. 1) The recently detected bissesquiterpenoids bovistol A-C are assembled by a Diels-Alderase, whose substrate spectrum will be determined by in vitro reactions. 2) Their illudin-precursors contain a three-membered ring structure, which is responsible for their strong cytotoxic effects. Despite the very broad distribution of this skeletal in fungi, the key ring contraction reaction catalysed apparently by P450-type monooxygenases remains an enigma. 3) A new viridiflorene-based diterpene is produced by C. aegerita, which is expected to be produced by the characterised STS Agr2. We will investigate whether this enzyme accepts geranylgeranyl pyrophosphate in addition to farnesyl pyrophosphate. Since we determine the structures and bioactivities of both volatile and non-volatile secondary metabolite products, we will not only further tap the secondary metabolome of the edible mushroom C. aegerita, but also seek to understand the terpenoid biosynthesis of a typical Basidiomycota in general.