Roses Are Red, Violets Are Blue, but Scientists Just Made Roses Bluer Too

Four borrowed genes helped roses manufacture both blue pigments and their molecular partners.

The blue rose has always been something of a botanical cheat since the world’s first genetically engineered blue rose was reported in 2004. Despite the name, flowers sold as blue have generally bloomed in shades of mauve, lavender or violet. Roses simply lack some of the molecular machinery that naturally blue flowers use.

Now researchers at the Suntory Global Innovation Center in Japan say they have pushed the rose closer to the elusive color by engineering not only blue pigments, but also the nearly colorless molecules that help those pigments actually look blue.

The resulting roses were classified as violet-blue on a standard flower color chart. The bushes continued producing the color through seven years of greenhouse testing in Japan and three years of field trials in Colombia.

The work was presented in August at the 32nd International Horticultural Congress in Kyoto.

Blue Is More Than a Pigment

Roses cannot naturally make delphinidin, an anthocyanin pigment associated with many blue and violet flowers. Anthocyanins are the same broad family of molecules that can produce red, purple and blue hues in petals, fruits and leaves.

Suntory researchers took this as a challenge. They looked at the rose and must have thought ‘this should be easy with genetic engineering.’ They were wrong. The scientists in Japan started work in 1990. But it wasn’t until 2004 that they announced genetically engineered roses capable of accumulating delphinidin. Finally, these were commercialized as SUNTORY blue rose APPLAUSE in 2009. But the flowers were more purple than blue.

Putting a blue pigment into a flower, scientists increasingly understood, is not the same thing as making a blue flower.

In many naturally blue flowers, anthocyanins interact with compounds called copigments. These molecules, often flavones or related chemicals, have little color themselves but associate with anthocyanins and can stabilize them while shifting the color toward blue. Decades of research have shown that petal acidity, metals and other surrounding molecules can also change what an anthocyanin looks like.

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Roses lack the necessary flavone C-glycoside copigments as well.

So, this time, the Suntory team engineered those, too.

Researchers introduced four genes into a light-pink rose. One, from Canterbury bells, helped the plant manufacture delphinidin-related pigments. Two genes from wishbone flowers and another from clustered gentian supplied enzymes needed to make flavone C-glycosides.

The strongest effect appeared when the pigment malvidin was paired with the copigment isoorientin. Roses containing more of these copigments tended to become progressively bluer. Both molecules accumulated inside the engineered petals and the coloration remained stable during three years of Colombian field trials.

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Borrowing a Trick From Other Blue Flowers

The approach has precedent. In a 2017 Science Advances study on genetically engineered blue chrysanthemums, researchers found that producing modified delphinidin pigments was not enough on its own. The flowers became blue when those pigments interacted with flavone compounds already present in the petals.

“Until now, a major focus in flower color modification has been which pigments can be produced in a plant,” said Seitaro Ito, who led the research. “In this study, we looked beyond pigment production itself and focused on the coloration mechanism — how the pigments produced interact with surrounding compounds and ultimately appear as flower color.”

The researchers are not claiming the quest is finished. Their roses are still violet-blue rather than the saturated azure of an iris or cornflower.

But after decades spent trying to give roses the right pigment, the experiment suggests the problem was bigger than pigment all along. To make a rose truly blue, scientists may have to engineer not one molecule, but an entire chemical environment around it.