Identification of the Sesquiterpene Cyclase Involved in the Biosynthesis of (+)-4-Epi-eremophil-9-en-11-ol Derivatives Isolated from Botrytis cinerea

Cultivation of the phytopathogenic fungus Botrytis cinerea using sublethal amounts of copper sulfate yielded a cryptic sesquiterpenoids family, which displayed the basic chemical structure of (+)-4-epi-eremophil-9-ene. The biosynthesis pathway was established, and the route involved the likely transformation of the diphosphate of farnesyl (FDP), to give a cis-fused eudesmane cation, through (S)-hedycaryol, finally yielding the (+)-4-epi-eremophil-9-enol derivatives. An expression study of genes that code for the sesquiterpene cydases (STC), including the recently reported gene Bcstc7 present in the B. cinerea genome, was performed in order to establish the STC involved in this biosynthesis. The results showed a higher expression level for the Bcstc7 gene with respect to the other stc1-5 genes in both wild-type strains, B05.10 and Botrytis cinerea UCA992. Deletion of the Bcstc7 gene eliminated (+)-4-epi-eremophilenol biosynthesis, which could be re-established by complementing the null mutant with the Bcstc7 gene. Chemical analysis suggested that STC7 is the principal enzyme responsible for the key step of cyclization of FDP to eremophil-9-en-11-ols. Furthermore, a thorough study of the two wild-types and the complemented mutant revealed four new eremophilenol derivatives whose structures are reported here.