Poets are captivated by the fragrance of flowers. So are scientists. A rather prosaic answer to the source of fragrance — for one species at least — is that it has a lot to do with the ODORANT1 gene (see Plant Cell doi:10.1105/tpc.104.028837; 2005).
Julian C. Verdonk et al. have studied Petunia hybrida (pictured), which emits its scent at night to attract its nocturnal pollinators, hawkmoths. The scent consists of a combination of volatile benzenoid compounds. The chain of precursors from which benzenoids are produced is well understood, but what's less clear is why their synthesis and release peak at night.
To find out, Verdonk et al. compared the genes expressed in flowers that were producing scent with those from flowers that were just about to produce scent and those from a different P. hybrida cultivar that emits low levels of benzenoids. This led the authors to a gene that they have called ODORANT1 (ODO1), whose activity is increased in the fragrant flowers at the appropriate time of day.
Sequence comparisons suggested that the protein encoded by ODO1 is a gene regulator. Indeed, eliminating ODO1 expression led to decreased expression of several other genes, whose protein products catalyse early steps in the benzenoid-synthesis pathway. Benzenoid production was also decreased. Curiously, however, there was no effect on flower colour, even though one of the benzenoid precursors is also involved in making floral pigments. That tallies with the idea that pigment production occurs at an earlier developmental stage than scent synthesis, and so is unaffected by the later experimental interference with ODO1 expression.
That won't be the end of this scented story, however. One obvious question is how ODO1 itself is turned on at the right time. Another is how its protein product interacts with its target genes — does it do so directly or through other factors? And can the scent of other plant species be attributed to ODO1 activity?