Rose floral scent

The rose is the queen of flowers and is widely used as a garden plant and for the cut flower market. Roses are also used for the production of essential oil for the cosmetic and perfume industries. A lot of botanical roses are scented and use their volatiles to attract pollinators. Fragrances in garden roses are very diverse and scent has always been an important character in the selection process. Breeders have recently tried to introduce new fragrances, for instance reminiscent of fruit or spice odors. But despite their efforts, some roses on the market are not very fragrant, especially the ones bred for the cut flower market. The cause of this lack of scent is not known. In modern roses or Hybrid Tea roses, scent is mainly produced by petals, although stamens can also contribute to the emission. Scent compounds are concentrated in rose petal epidermis, probably in small lipid droplets. In spite of numerous chemical studies, the biosynthetic pathways of many rose scent compounds are unknown. We are studying several genes involved in the biosynthesis of scent in rose. For example, we recently characterized the enzymes responsible for the so-called "tea scent" emitted by Chinese roses. Apart from "tea scent", terpenoids, especially monoterpenes, are also major constituents of rose flowers, mostly responsible for the "typical rose scent". Generally, terpenoids biosynthesis in plants is achieved by various terpene synthases. However, with a combination of transcriptomic and genetic approaches, our group recently discovered a terpene synthase-independent pathway. A key enzyme of this pathway is RhNUDX1, belonging to the Nudix protein family. It has geranyl diphosphate diphosphohydrolase activity in vitro. A positive correlation was found between the expression levels of RhNUDX1 and the production of the monoterpene geraniol, indicating the essential role of this protein in scent production in roses.