Unravelling the Function of the Sesquiterpene Cyclase STC3 in the Life Cycle of <em>Botrytis cinerea</em>

The genome sequencing of Botrytis cinerea has supplied a general overview of the map of genes involved in secondary metabolite synthesis. B. cinerea genomic data have revealed that this phytopathogenic fungus has seven sesquiterpene cyclase (Bcstc) genes that encode proteins involved in the farnesyl diphosphate cyclization. Three sesquiterpene cyclases (BcStc1, BcStc5 and BcStc7) have been characterized, related to the biosynthesis of botrydial, abscisic acid and (+)-4-epi-eremophilenol, respectively. However, the role of the other four sesquiterpene cyclases (BcStc2, BcStc3, BcStc4 and BcStc6) remains unknown. BcStc3 is a well-conserved protein with homologues in many fungal species, and here, we have undertaken its functional characterization in the life cycle of the fungus. A null mutant ΔBcstc3 and an overexpressed–Bcstc3 transformant (OvBcstc3) were generated, and both strains show deregulation of those other sesquiterpene cyclase-encoding genes (Bcstc1, Bcstc5, Bcstc7). These results suggest a co-regulation of the expression of the sesquiterpene cyclase gene family in B. cinerea. Phenotypic characterization of both transformants revealed that BcStc3 is involved in oxidative stress tolerance, production of reactive oxygen species and virulence. The metabolomic analysis allowed the isolation of characteristic polyketides and eremophilenols from the secondary metabolism of B. cinerea, although no sesquiterpenes different from those already described were identified.