Scent engineering: toward the goal of controlling how flowers smell.

Floral scent has an important role in the reproductive processes of many plants and a considerable economic value in guaranteeing yield and quality of many crops. It also enhances the aesthetic properties of ornamental plants and cut flowers. Many floral scent volatiles fall into the terpenoid or phenylpropanoid/benzenoid classes of compounds. Although the biochemistry of floral scent is still a relatively new field of investigation, in the past decade investigators have begun to identify 'scent genes'. Several of these genes, most of which, but not all, encode enzymes that directly catalyze the formation of volatile terpenoid or phenylpropanoid/benzenoid compounds, have now been used to manipulate, through genetic engineering techniques, the mix of volatiles emitted from the flowers of several plant species. The outcomes of these experiments, which are discussed here, have indicated that the genetic engineering approach to altering floral scents has potential; however, they have also revealed the limitations that result from our inadequate knowledge of the metabolic pathways responsible for scents and their regulation.