Petunias release their scent following the daily rhythm of a circadian-clock gene.

Takato Imaizumi of the University of Washington in Seattle and his colleagues identified a gene that they call PhLHY in the fragrant flower Petunia hybrida, which releases volatile scent molecules primarily at night.

This gene is typically expressed in the morning, dampening the expression of other genes and the production of enzymes involved in producing scent molecules.

Plants engineered to constantly express PhLHY stop producing scent molecules entirely. By contrast, plants in which this gene's expression is reduced show peak scent production around midday.

Proc. Natl Acad. Sci. USA http://doi.org/5xg (2015)