Without this key molecule, you wouldn't be able to smell the roses

Geraniol is widely used in the cosmetic and perfume industry after it is derived from essential oils of various plant species it is present in.

Geraniol is produced via a chemical reaction involving FPP synthase and several other enzymes like NUDX1 hydrolase. A flower-like rose needs a lot of NUDX1 hydrolase to create a long-lasting scent. And this is only possible when there is enough geranyl diphosphate (GPP) around, which glues itself to NUDX1 hydrolase to propel it into action.

Most plants keep NUDX1 hydrolase and GPP in another area called the plastids. So where do roses get the GPP to make geraniol?

Popular Science spoke to the research team and found they studied the biochemical reactions inside a particular rose of Chinese origins called Old Blush. The team isolated various parts of the rose to rule out different ways the plant could produce geraniol. If the rose stopped making geraniol or produced low amounts, it would be a tell-tale sign of the role of that particular pathway in supplying GPP. On the other hand, the team could rule out a process if geraniol continued to be made at normal levels.

Natalia Dudareva, the director of the Center for Plant Biology at Purdue University and one of the study's coauthors, told Popular Sciences that inhibitors blocked the plant’s ability to express the enzyme called FPP synthase protein, it decreased geraniol levels. The enzyme created two chemical compounds, and it's capable of producing GPP too. Dudareva added that FPP synthase must have evolved long ago to produce more readily available GPP.

Senior author Benoît Boachon, a plant biochemist at the French National Centre for Scientific Research, says by isolating FPP synthase, the smell of roses can be reintroduced in the flowers that may have lost their scent.

The study was published on May 1, 2023, in the peer-reviewed journal PNAS.

Study abstract:

Geraniol derived from essential oils of various plant species is widely used in the cosmetic and perfume industries. It is also an essential trait of the pleasant smell of rose flowers. In contrast to other monoterpenes which are produced in plastids via the methyl erythritol phosphate pathway, geraniol biosynthesis in roses relies on cytosolic NUDX1 hydrolase which dephosphorylates geranyl diphosphate (GPP). However, the metabolic origin of cytosolic GPP remains unknown. By feeding Rosa chinensis “Old Blush” flowers with pathway-specific precursors and inhibitors, combined with metabolic profiling and functional characterization of enzymes in vitro and in planta, we show that geraniol is synthesized through the cytosolic mevalonate (MVA) pathway by a bifunctional geranyl/farnesyl diphosphate synthase, RcG/FPPS1, producing both GPP and farnesyl diphosphate (FPP). The downregulation and overexpression of RcG/FPPS1 in rose petals affected not only geraniol and germacrene D emissions but also dihydro-β-ionol, the latter due to metabolic cross talk of RcG/FPPS1-dependent isoprenoid intermediates trafficking from the cytosol to plastids. Phylogenetic analysis together with functional characterization of G/FPPS orthologs revealed that the G/FPPS activity is conserved among Rosaceae species. Site-directed mutagenesis and molecular dynamic simulations enabled to identify two conserved amino acids that evolved from ancestral FPPSs and contribute to GPP/FPP product specificity. Overall, this study elucidates the origin of the cytosolic GPP for NUDX1-dependent geraniol production, provides insights into the emergence of the RcG/FPPS1 GPPS activity from the ancestral FPPSs, and shows that RcG/FPPS1 plays a key role in the biosynthesis of volatile terpenoid compounds in rose flowers.