Roses are red, and a variety of other colors.
But they've never been blue — an omission legions of rose breeders have sought for centuries to remedy.
"It would be a beautiful thing to see," said James Armstrong, an award-winning flower show exhibitor and consultant with the San Francisco Rose Society.
Breakthroughs in biotechnology may finally resolve the quest for the elusive blue rose, which, alas, does not exist because roses lack the corresponding pigment genes.
Technology also promises to restore sweet smells to the rose and other flowers. Generations of commercial breeding has led to beautiful but bland-smelling roses. Their colors are stunning and vase lives long, but they've little fragrance.
Genetic engineers are also busy bringing science to bear on diseases and pests that affect the world's 120 different rose species, which have blossomed into a $10 billion-a-year business worldwide.
Still, it's the blue rose that remains the biggest prize.
At Vanderbilt University School of Medicine, scientists studying how drugs metabolize in the liver stumbled across a human protein that may hold the key to creating the world's first-known blue rose.
Elizabeth Gillam, working in the lab of biochemist F. Peter Guengerich, amazed her boss one day with a flask full of bacteria that she turned blue with an enzyme taken from a patient's liver. They're now trying to insert into roses the human gene that produces that blue enzyme.
"I would have called you crazy five years ago if you told me I would be pursuing a blue rose," said Guengerich, who spends most of his time researching disease-fighting drugs. "It's not something we set out to do."
Guengerich marvels that so many gardening enthusiasts lust after the blue rose, the pursuit of which has reached near-mythical proportions.
"For some reason this is the holy grail for this type of work," Guengerich said. "We could try to create blue cotton, blue anything really."
So far, though, they've only managed to get a few blue spots into the stems. "It's not as easy you may think," Guengerich said. "It's going to take more work."
Guengerich and Gillam are nonetheless talking to biotechnology companies about helping them develop a blue rose.
They're not alone — Florigene, an Australian company, was launched in 1986 to develop a blue rose. Its scientists have tried to splice a "blue" petunia gene into roses, with little success so far.
Sweeter-smelling roses are perhaps closer to market. Researchers around the world are working to identify scent genes in roses and other flowers. A key step has been mapping their genomes.
A group of Israeli researchers published a paper in the journal Plant Cell in September that compared the genome of the strong-scented Fragrant Cloud rose to that of the nearly odorless yellow rose. Then, they isolated genes that occurred only in the fragrant rose and may be responsible for scent.
The trick now is to splice the scent genes into non-fragrant varieties, a not-so-easy task.
"Unfortunately, we don't have the technology to transform the rose," David Weiss of the Hebrew University of Jerusalem, co-author of the Plant Cell paper, said in an e-mail interview. "We are working on it."
At Clemson University, researcher Sriyani Rajapakse has developed DNA "fingerprints" so growers can protect their special rose breeds from being stolen. She also has produced a rough draft of the entire rose genome.
Rajapakse said rose genomes will allow growers to more easily and quickly weed out undesirable plants. Now, growers typically have to wait until all of their roses bloom to decide which plants to keep and which to discard.
"Biotechnology holds great promise for roses," Rajapakse said.
Among other biotechnology projects that may soon be under way is the creation through genetic engineering of thornless roses. Robert Skirvin, a professor at the University of Illinois at Urbana-Champaign, hopes his work with thornless blackberry bushes can be used to de-thorn the stems of brambled rose varieties.
Other research in various stages could add more panache to the ornamental flower industry. Of the top ten selling flowers, only the freesia has a naturally occurring blue variety.
While there's growing criticism of biotechnology's use on crops to produce food and pharmaceuticals, protest against tinkering with flowers' genes has been muted. That's probably because flowers aren't generally being consumed.
A few complaints have come from purists, but serious hobbyists like Armstrong of the San Francisco Rose Society view biotechnology a great way to grow better, hardier flowers.
"They still have to be extremely careful that there isn't inadvertent hybridization," said Armstrong, who exhibits roses in shows. "But I'm not a purist. It would be nice to see a blue rose and the only way that's going to happen is through genetic engineering."
Biotech goal: sweet-smelling blue roses, by PAUL ELIAS, AP Biotechnology Writer.