Metabolic engineering of tomato fruits for production of raspberry ketone glycosides

Raspberry ketone is a valuable aromatic compound that occurs only at trace levels in natural sources. In this study, transgenic tomato fruits expressing benzalacetone synthase (BAS) from Rheum palmatum and raspberry ketone/zingerone synthase 1 (RZS1) from Rubus idaeus under the CaMV 35S promoter accumulated raspberry ketone (9.9-19.3 μg g^-1 fresh weight) together with minor amounts of rhododenol (2.7-4.4 μg g^-1 fresh weight), predominantly as glycosides during fruit ripening. LC-MS/MS analysis using an authentic standard identified raspberry ketone monoglucoside as a major glycosylated form present in transgenic fruits but absent in wild-type controls. Raspberry ketone glycosides were predominantly detected in the fruit peel, with negligible levels in the flesh, seeds, or leaves. Co-expression of the Arabidopsis thaliana R2R3-MYB transcription factor AtMYB12 further enhanced raspberry ketone production, reaching up to 88 μg g^-1 fresh weight. These results demonstrate effective metabolic redirection of phenylpropanoid flux in an edible fruit tissue and establish tomato as a viable heterologous host for raspberry ketone production. This metabolic engineering strategy highlights the potential of edible fleshy fruits as sustainable plant-based platforms for the biosynthesis of high-value aromatic phenolics.