Genes and enzymes involved in strawberry flavor formation

Strawberry (Fragaria x ananassa) aroma consists of a blend of hundreds of components but only a handful are considered as key flavor compounds. The most important is 4-hydroxy-2,5- dimethyl-3(2//)-furanone (HDMF) but during the ripening process it is metabolized further by FaOMT (Fragaria x ananassa O-methyltransferase) to 2,5-dimethyl-4-methoxy- 3(2#)-fiiranone (DMMF). We have discovered the first enzyme involved in the biosynthesis of HDMF in strawberries. The protein was partially purified and peptide sequence analyses of the digested protein showed total identity with the corresponding sequences of a strongly ripening induced, auxin-dependent putative quinone oxidoreductase (FaQR). The recombinant FaQR protein, expressed in E. coli catalyzed the formation of HDMF from a novel metabolite. In addition, we showed that Agrobacterium-medizlQd transformation of strawberry with the Fragaria x ananassa O-methyltransferase (FaOMT) gene in sense and antisense orientation, under the control of a constitutive promoter resulted in a nearly complete loss of DMMF. The levels of the other volatiles remained unchanged. For the first time strawberry flavor has been successfully modified by genetic engineering.