Navigating the network of floral scent production

Flower fragrance is a composite character determined by secondary metabolites of diverse biosynthetic origin. Together with other traits, such as flower color, it is used by plants to lure pollinators and seed dispersers, thus ensuring plant survival. Research into the regulatory mechanisms leading to floral scent production/emission is still in its infancy and even less is known regarding flow within and crosstalk between secondary metabolic pathways leading to floral scent production. Using transgenic plants modified in anthocyanin production, we revealed an intriguing interrelationship between the branches of the phenylpropanoid pathway leading to the production of anthocyanins and volatiles. Specifically, we recorded five- to seven-fold higher levels of the volatile phenylpropanoids methyl benzoate and 2-hydroxymethyl benzoate in flavanone 3-hydroxylase (F3h)-suppressed carnation flowers with dramatically reduced anthocyanin levels, as compared to control non-transgenic flowers. Furthermore, overexpression in petunia flowers of the transcriptional regulator Pap1 (production of anthocyanin pigment 1), which activates the phenylpropanoid pathway, led to increases in both anthocyanin accumulation and volatile phenylpropanoid emission. Using virus-induced gene silencing (VIGS) for large-scale identification of floral scent genes, we further characterized metabolic flow within the pathway. The advantages of VIGS and of petunia as a model plant create a solid infrastructure for the future isolation of regulatory factors involved in floral scent production/emission. Knowledge gained from an understanding of mechanisms leading to floral scent production/emission should provide us with better insight into nature's way of ensuring evolutionary success, as well as with advanced tools for the metabolic engineering of fragrance.