Metabolic engineering in strawberry fruit uncovers a dormant biosynthetic pathway

Wild strawberry (Fragaria vesca) fruit contains several important phenylpropene aroma compounds such as eugenol, but cultivated varieties are mostly devoid of them. We have redirected the carbon flux in cultivated strawberry (Fragaria×ananassa) fruit from anthocyanin pigment biosynthesis to the production of acetates of hydroxycinnamyl alcohols, which serve as the precursors of the phenylpropenes, by downregulating the strawberry chalcone synthase (CHS) via RNAi-mediated gene silencing and, alternatively, by an antisense CHS construct. Simultaneous heterologous overexpression of a eugenol (EGS) and isoeugenol synthase (IGS) gene in the same cultivated strawberry fruits boosted the formation of eugenol, isoeugenol, and the related phenylpropenes chavicol and anol to concentrations orders of magnitude greater than their odor thresholds. The results show that Fragaria×ananassa still bears a phenylpropene biosynthetic pathway but the carbon flux is primarily directed to the formation of pigments. Thus, partial restoration of wild strawberry flavor in cultivated varieties is feasible by diverting the flavonoid pathway to phenylpropene synthesis through metabolic engineering.