A rose by any other name would smell as sweet, as Shakespeare wrote, but erase just one little molecule in their flowers and you’d be lucky to catch a whiff of anything at all. In recent decades, commercial gardeners have bred roses that grow in different colors, are more insect-resistant, and have a longer vase life. But that manipulation has a trade-off: more visually appealing flowers often lose their strong aromatic fragrances.
What do roses need to make their pleasant odors, 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 for driving the reaction that creates a rose’s fresh and floral scent. The findings could help with finding a way to create more mesmerizing and beautiful roses.
A chemical called geraniol is responsible for the sweet scent we associate with roses. Roses make the compound through a chemical reaction that involves FPP synthase plus several other enzymes. The process involves NUDX1 hydrolase, an enzyme found in the liquid interior of plant cells, or cytosol, that make up the rose petals. To create a strong and sweet aroma, flowers need a ton of NUDX1 hydrolase activity. This is only possible when there is enough of a binding molecule called geranyl diphosphate (GPP). GPP glues to the enzyme and propels it into action.
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But in order for this process to work, the binding molecule needs to be nearby. This isn’t the case for roses. Senior author Benoît Boachon, a plant biochemist at the French National Centre for Scientific Research, says most plants keep GGP and NUDX1 hydrolase in another area called the plastids. These organelles act as key sites for photosynthesis. This motivated Boachon and his colleagues to figure out where roses get the GPP to make geraniol. He hypothesizes that GPP could have some mechanism transporting it from the plasmid to the cytosol, or there’s another pathway for the flower to generate its own supply of GPP.
To solve the plant mystery, the study authors studied the biochemical reactions that take place in a variety of pink roses called Old Blush. They isolated different plant parts and shut down chemical pathways involved with the creation or release of geraniol. If the altered roses no longer made geraniol, or the plants produced it in low amounts, that was a major clue to the scientists—they’d found a pathway that plays a role in supplying GPP. On the other hand, the team could rule out a process if geraniol continued to be made at normal levels.
Their search led them to a particular pathway in plant cytosol–where they took interest in a second, unknown role of the FPP synthase protein. When inhibitors blocked the plant’s ability to express this enzyme, it decreased geraniol levels.
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The enzyme was found to create two chemical compounds. Plant scientists have known that it makes a chemical related to GPP, called farnesyl diphosphate, which contributes to a rose’s sweet smell. But the study’s biochemical analysis reveals the enzyme is capable of producing GPP as well. Natalia Dudareva, the director of the Center for Plant Biology at Purdue University and one of the coauthors of the study, says that roses must have evolved FPP synthase long ago to produce more readily available GPP. Protein sequencing of the enzyme revealed two amino acids that may have mutated to allow it to produce GPP instead of converting all the GPP to farnesyl diphosphate.
The next step was to see if the FPP synthase enzyme produced similar effects inside a plant in real time. They engineered tobacco leaves to express this enzyme and the chemical pathway used for making geraniol. As they 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 aroma of commercially grown roses. And by isolating the enzyme, Boachon says one potential application is to metabolically reintroduce the sweet fragrance into roses that have lost their iconic smell over time.