Monks once hoped to turn lead into gold through alchemy. But consider the cauliflower instead. It only takes two genes to transform the common stems, stems and flowers of the weed, tasteless species Brassica oleracea into a formation as wonderful as this fractal, cloud-like vegetable.
This is true alchemy, says Christophe Godin, senior researcher at the National Institute for Research in Digital Science and Technology in Lyon, France.
Dr. Godin studies plant architecture by practically modeling the evolution of different species in three dimensions. He wondered what genetic modification lay behind the cauliflower̵
“How is nature capable of building such unexpected objects?” he asked. “What could the rules behind this be?”
Fifteen years ago, Dr. Godin met François Parcy, a plant biologist at the National Center for Scientific Research in Grenoble, France. In Dr. Parcy recognized Dr. Godin a colleague for fractal flowers.
“There’s no way you can not notice that it is such a beautiful vegetable,” said Dr. Parcy, with reference to Romanesco.
Drawn from a passion for Brassica, Dr. Godin and Dr. Parcy, the genetic mystery of the fractal geometry in both Romanesque and ordinary cauliflower, evoked the plants in mathematical models and also grew them in real life. Their results, which suggest that the fractals are formed in response to shifts in networks of genes that control flower development, will be published Thursday in Science.
“It’s such a good integration of genetics on the one hand and strict modeling on the other,” said Michael Purugganan, a biologist at New York University who was not involved in the research. “They’re trying to show that by adjusting the rules of how genes interact, you can make dramatic changes to a plant.”
In the early 2000s, Dr. Parcy that he understood the cauliflower. He even taught classes about its flower development. “What is a cauliflower? How can it grow? Why does it look like this? ” he said.
Cauliflower, like Brussels sprouts, comes from centuries of selective breeding of Brassica oleracea. Humans bred Brussels sprouts for lateral buds and cauliflower for flower clusters. Cauliflower, however, does not produce flower buds; their inflorescences or flower-bearing shoots never ripen to produce flowers. Instead, cauliflower blooms generate replicas of themselves in a spiral, creating clusters of curd like plant-based cottage cheese.
When the two researchers discussed cauliflower, Dr. Godin, that if Dr. Parcy really understood the plant, should it be easy to model the morphological development of the vegetable. As it turned out, it was not.
The two first confronted the colliding ant on the board and sketched various diagrams of genetic networks that could explain how the vegetable mutated to its current form. Their muse was Arabidopsis thaliana, a well-studied weed in the same family as cauliflower and its many cousins.
If a cauliflower has a single cauliflower at the base of the plant, Arabidopsis has many cauliflower-like structures along its elongated stem. But what genes could refine these smaller cauliflowers into a magnificent, compact cauliflower? And if they identified these genes, could they then wring these cauliflowers into the peaks that Romanescos formed?
To answer these questions, the researchers would adapt the gene network and run it through mathematical models, generate it in 3D and mutate it in real life. “You imagine something, but until you program it, you do not know what it will look like,” said Dr. Parcy.
(During the study, Dr. Parcy also collected several specimens of Romanesco from his local farmers market, sequenced and dissected them. He and his colleagues then ate on the leftovers, usually raw with various dips along with glasses of beer.)
Many initial models flopped and did not look like cauliflower. At first, the researchers thought the key to the cauliflower lay in the stem. But when they programmed Arabidopsis with and without a short stalk, they realized that they did not need to reduce the stalk size of the cauliflower, neither in the 3D models nor in real life.
And the cauliflowers, the ones simulated and grown, were simply not fractal enough. The patterns were only visible in two fractal scales, such as a spiral embedded in another spiral. In contrast, an ordinary cauliflower often shows similarity on at least seven fractal scales, meaning a spiral embedded in a spiral embedded in a spiral embedded in a spiral embedded in a spiral embedded in a spiral embedded in, ultimately, another spiral.
So instead of focusing on the stem, they concentrated on the meriston, an area of plant tissue at the tip of each stem where actively dividing cells produce new growth. They assumed that making the meristem larger would increase the number of shots produced.
The only problem was that the researchers did not know which gene could control the meristem’s rate of shoot production.
One day, Eugenio Azpeitia, then a postdoctoral fellow in Dr. Godin’s laboratory, remembered a gene known to change the size of the meristem’s central zone. The three researchers enjoyed a brief moment of euphoria and then waited patiently for several months for their newly modified Arabidopsis to grow. When the shoots sprouted, they had cauliflower with distinct conical tips.
“Very reminiscent of what’s happening in Romanesco,” said Dr. Goddess proud.
Usually when a plant germinates a flower, the flowering tip of the plant prevents more growth from the stem. A cauliflower mass is a bud that is designed to become a flower, but which never quite gets there and instead takes a shoot. But the researchers’ experiments in the meristem found that because this shoot has passed a transient flowering stage, it is exposed to a gene that triggers its growth. “Because you have been a flower, you are free to grow and you can make a shoot,” said Dr. Parcy.
This process creates a chain reaction where the meristem creates many shoots, which in turn creates many more shoots that adopt a cauliflower fractal geometry.
“It’s not a normal tribe,” said Dr. Goddess. “It’s a stalk without a leaf. A stalk without inhibition. ”
“It’s the only way to make a cauliflower,” said Dr. Parcy.
Researchers say there are likely other mutations responsible for the spectacular form of Romanesco. Ning Guo, a researcher at the Beijing Vegetable Research Center who is also studying the potential genetic mechanism behind the architecture of cauliflower architecture, says the paper has offered “a lot of inspiration.”
“The story is not over yet,” said Dr. Godin and added that he and Dr. Parcy will continue to refine their cauliflower models. “But we know we’re on the right track.”
But they are open, they say, to studying everything that flourishes.