It’s harder to stop and smell the roses these days, and not just because modern life is hectic. Thanks to generations of breeding for looks, roses’ scents have faded. Now, a team of geneticists say they’ve found the gene that gives roses their scent, and that discovery may help rose breeders produce sweeter-smelling roses again.
Roses’ fading scent
When you sniff a rose, you’re inhaling a mixture of hundreds of chemical compounds that add up to a pleasant scent. Most of those nice-smelling compounds are alcohols called monoterpenes.
But many modern rose cultivars don’t produce as many monoterpenes as their ancestors once did. Natural selection originally put pressure on roses to evolve a sweet scent that would attract pollinators, but when rose breeders stepped in instead, things changed.
“Rose breeders have focused on the most commercially important characteristics,” explained geneticist and study co-author Philippe Hugueney. Today’s roses were bred for attractive looks and flowers that can stay fresh in a vase for a long time. Since they’re a commercial crop, they were also bred for disease resistance and the ability to survive transport around the world.
“Scent has not been a priority; therefore, it has been lost over the breeding process,” Hugueney said.
An enzyme by any other name
Now, many rose breeders want to restore scent to their flowers, Hugueney said, especially those who sell roses for the cut flower market. To do that, they’ll need to understand the genetics behind that sweet scent.
For some of the less important compounds in rose scent, scientists already knew the answers. But they didn’t know the genetic basis of the monoterpenes that account for as much as 70% of the scent of some cultivars, like the heavily scented Papa Meilland variety.
To find it, the team of researchers didn’t just stop and smell the roses, they studied their genomes. In particular, they compared the genomes of Papa Meilland roses and scentless Rouge Meilland roses, looking for differences that might provide a clue about why one rose smelled and the other didn’t.
They found that the biggest difference was in a gene called RhNUDX1. They then inspected ten other rose varieties and confirmed their suspicion: roses that strongly expressed the gene produced more monoterpenes and had stronger scents.
It turns out that roses use the RhNUDX1 enzyme to make a monoterpene called geraniol, which is the main component of rose oil, the researchers report this week in Science.
Smell the roses again
Hugueney and his colleagues hope their discovery might help bring back scented roses. Since scentless roses still have the RhNUDX1 gene but have it turned off, rose breeders may be able to turn it back on to produce sweeter-smelling roses.
And it doesn’t look like that will conflict with breeding for looks and vase life. The researchers didn’t find any genetic link between scent and vase life in the roses they studied.
Breeders could also try more futuristic approaches. Hugueney said they could produce genetically modified roses, designed to heavily express the gene and produce a stronger scent, although they might not be accepted in some markets, like Europe. And in theory, it could someday even be possible to drop the gene into a genetically modified microbe to produce rose oil for perfumes and cosmetics – but that’s just speculation for now.