Chemists Finally Uncover the Secret to a Rose’s Iconic Scent

A rose by any other name would smell just as sweet, as Shakespeare wrote, but erase just one tiny molecule in its blossoms and you’ll be lucky to catch a whiff of anything. In recent decades, commercial gardeners have cultivated roses that grow in different colors, are more resistant to insects, and have a longer vase life. But there’s a trade-off to that manipulation: the most attractive flowers to look at often lose their strong aromatic fragrances.

What do roses need to produce their pleasant scents, and more importantly, how do we get them back? A new study published Monday in PNAS identified a key enzyme called farnesyl diphosphate (FPP) synthase, crucial in driving the reaction that creates the fresh, floral scent of a rose. The findings could help find a way to create more fascinating and beautiful roses.

A chemical called geraniol is responsible for the sweet scent we associate with roses. Roses produce the compound through a chemical reaction involving FPP synthase in addition to several other enzymes. The process involves NUDX1 hydrolase, an enzyme found in plant cells’ liquid interior, or cytosol, that make up rose petals. To create a strong, sweet aroma, flowers need a lot of NUDX1 hydrolase activity. This is only possible when there is enough of a binding molecule called geranyl diphosphate (GPP). GPP binds to the enzyme and drives it into action.

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But for this process to work, the binding molecule must be close. This is not the case with roses. Lead author BenoƮt Boachon, a plant biochemist at the French National Center for Scientific Research, says that most plants maintain GGP hydrolase and NUDX1 in another area called plastids. These organelles act as key sites for photosynthesis. This motivated Boachon and his colleagues to find out where roses get the GPP to produce geraniol. He hypothesizes that GPP might have some mechanism that transports it from the plasmid to the cytosol, or that there is another pathway for the flower to generate its own supply of GPP.

To solve the mystery of the plant, the study authors studied the biochemical reactions that take place in a variety of pink roses called Old Blush. They isolated different parts of the plant and shut down the chemical pathways involved in creating or releasing geraniol. If the altered roses no longer produced geraniol, or the plants produced it in low amounts, that was an important clue for the scientists: They had found a pathway that plays a role in the supply of GPP. On the other hand, the team could rule out a process if geraniol continues to be produced at normal levels.

Their search led them to a particular pathway in the plant cytosol, where they became interested in a second unknown role for the FPP synthase protein. When inhibitors blocked the plant’s ability to express this enzyme, geraniol levels dropped.

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The enzyme was found to create two chemical compounds. Plant scientists have known that it produces a chemical related to GPP, called farnesyl diphosphate, which contributes to a rose’s sweet smell. But the biochemical analysis of the study reveals that the enzyme is also capable of producing GPP. Natalia Dudareva, director of Purdue University’s Center for Plant Biology and one of the study’s co-authors, says roses must have evolved FPP synthase long ago to make more available GPP. Protein sequencing of the enzyme revealed two amino acids that may have been mutated to allow it to make GPP instead of converting all GPP to farnesyl diphosphate.

The next step was to see if the FPP synthase enzyme produced similar effects within a plant in real time. They engineered tobacco leaves to express this enzyme and the chemical pathway used to produce geraniol. As expected, the tobacco leaves where they found the enzyme produced both GPP and farnesyl diphosphate.

Understanding the essential players involved in fragrance making could restore the scent of commercially grown roses. And by isolating the enzyme, Boachon says one potential application is metabolically reintroducing the sweet fragrance to roses that have lost their iconic scent over time.

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