University of Florida researchers are securing the future of floral fragrance using caladium

Photo © David / Adobestock

Draw close to an aromatic shrub or a fragrant, fresh-cut bouquet, and you may experience several things: the pleasure of the fragrance itself, grounded in the present, or a montage of memories evoked by the scent.

That is unless you’re Thomas A. Colquhoun, Ph.D. (pronounced Calhoon), a University of Florida associate professor of plant biotechnology doing cutting-edge research in floral fragrance.

“I can smell some sulfur compounds, but other than that, I got nothing,” he says, with a laugh.

Despite his olfactory limitations — or because of them — Colquhoun was drawn to floral fragrance when he first came to UF to earn his Ph.D. in plant molecular and cellular biology. The self-proclaimed lab rat’s interest was piqued in his first project, identifying the production of floral volatiles in petunias. He began discovering the genetic secrets behind the floral fragrances the rest of world enjoys, and his interest grew.

Fragrant inspiration in an unexpected source

Photo courtesy of University of Florida

As Colquhoun worked more with floral fragrance, he learned more about the history of breeding roses. Many independent garden center operators and others in the horticultural industry understand all too well that many modern rose varieties lack the intoxicating fragrances of their predecessors.

Colquhoun learned how fragrance had been overlooked as rose breeding efforts focused on disease resistance, shipping tolerances and similar traits.

“That’s how the fragrance got bred out of roses,” he says. “That really sparked my interest. What if we could figure this out molecularly, genetically, and then be able to give that information to the breeders so that they could be paying attention to the fragrance in an easy way?”

Fast forward a bit — through several years of valuable research — to the day a UF colleague stopped by Colquhoun’s office with a paper from a small journal in hand. The paper was on caladium, a plant favored for foliage, not fragrance. The colleague asked him what was weird about the paper.

As Colquhoun explains, the caladium being studied only made a few volatiles. But the amount of one volatile known as 4-methyl-5-vinylthiazole (MVT) was stunningly high.

“The chemical structure of it made it so a plant shouldn’t be able to make that much,” he says. “It shouldn’t be able to happen. It was just insane.”

Chasing the chain of fragrance promotion

With the impossible suddenly possible, Colquhoun’s team set out to find answers to explain what the paper reported. Through their research, the lab figured out what was happening and why the expression of the gene that promoted the protein behind the volatile was, in his words, through the roof. That’s when it hit.

He determined that if he could harness the mechanism of that promoter — and whatever was turning it on — he could stick it in the floral fragrance gene of other plants. The idea was that it would then trigger high levels of the protein, which would in turn trigger volatile synthesis and seriously increase the fragrance of the recipient.

“As luck would have it, that’s what happened,” he says.

In research funded by American Floral Endowment, Colquhoun’s lab was able to establish proof-of-concept by successfully inserting the promoter gene from Caladium bicolor ‘Tapestry’ into a petunia, nearly doubling the petunia’s fragrance.

To be clear, it’s petunia fragrance, not caladium fragrance. He compares the process to swapping a car engine.

“I’m essentially swapping the engine out of a Porsche and putting it in a Chevy,” he explains. “So, we took this engine, we put it in petunia, driving a transcription factor named ODORANT 1, which is a main player in turning on all the fragrance genes in petunia when the flower opens. That created higher expression of a lot of the components of the biosynthetic pathway for fragrance in petunia, and it resulted in higher levels of fragrance.”

The team then used advanced techniques to successfully create stable, genetically engineered petunias that carried the fragrance-promoting gene through subsequent generations.

Looking to the next fragrance challenge

Now that the research has supported the idea of Colquhoun’s “gangbuster promoter from caladium” working to increase overall floral fragrance biosynthesis in petunia, new goals for his research are in sight.

While his research involves synthetic biology and transgenic techniques, Colquhoun believes the work unveiled fundamental knowledge about fragrance production that can assist traditional breeders in their work. And, of course, it also holds the promise of returning intoxicating fragrances to roses and other plants without spending decades in traditional breeding programs.

Looking to the future, Colquhoun foresees the ability to use genetic engineering to “swap the engine” in roses, for example, and target the production not only of fragrance in general but to tailor volatile production for specific fragrances desired.

“It has been my career goal to understand and manipulate floral fragrance to satisfy consumers,” Colquhoun says.

Though he won’t enjoy the fragrances himself, he will experience the joy that enhanced floral fragrances bring to others.

Jolene Hansen is a freelance writer specializing in the horticulture, floriculture and CEA industries. Contact her at jolene@jolenehansen.com.