Geneticists Find Switch That Makes Plants Bloom : Science: One gene is enough to turn roots or thorns into petals. Discovery has huge potential for agriculture.

In the cells of the mustard weed and the trembling aspen, scientists have discovered the master genetic switch that makes plants bloom, giving gardeners the potential to turn the rose’s thorn into a flower and farmers the ability to speed their crops to harvest.

Two groups of scientists at the Salk Institute for Biological Studies and at UC San Diego independently demonstrated in research made public Wednesday that only a single gene is needed to turn what might normally be cells of roots, thorns, stems or leaves into flowers.

It is a revolution in a flower pot.

“We have virtually complete control over the onset of flowering,” said Martin Yanofsky, the senior scientist on the UC San Diego research group.

By activating that molecular switch, the researchers showed they also can reset a plant’s biological clock to make it flower much earlier than normal.

An aspen tree, for example, normally does not bloom until it is about a decade old and 30 feet tall, but Salk researchers are able to make it bear flowers when it is still a seedling barely 5 months old and two inches high. The Salk group is the first to succeed in accelerating the flowering of trees, said National Science Foundation officials who funded the work.

“We were completely surprised, I must say,” Detlef Weigel, the biologist who led the Salk team, said. “The dogma was that you just cannot induce flowers in young trees.”

Experts said that the work is much more than a horticultural curiosity.

Virtually every important crop produces flowers as part of its development before yielding the fruits and cereals on which most people depend for nutrition. “Rice and corn flowers are not very impressive, but they are flowers nonetheless,” Weigel said.

Control of flowering could give farmers the ability to change when crops come to harvest. If crops are threatened by an unseasonable frost, for example, growers could spray genetically engineered plants with a harmless chemical that would activate the flowering gene and trigger an early harvest. The gene could also be used to increase crop yields by sharply reducing the time it takes a crop to flower and produce seed grains such as corn, wheat and rice.

Almost immediately, scientists could use the gene to accelerate the breeding of new trees and other long-lived plants by reducing the time it takes to cultivate new generations of seeds from plants modified in a laboratory greenhouse. Once a new plant variety was perfected, researchers could return it to a more normal growth cycle by deactivating the gene.

“This a fundamental step forward,” said Elliot Meyerowitz, a recognized authority at Caltech on plant genetics and flowering. “The practical applications are a wonderful side benefit.

“The application which could begin now is to speed up breeding programs in trees. We want better, more ecologically sound sources of paper now, not in 100 years. There also are huge shortages of timber. . . . If we could find ways to develop better trees agriculturally and grow them, we would not have to cut down the old forests we have now.”

The new work, published in the journal Nature, involves two genes that have been known to play a key role in flowering. The Salk group focused its efforts on a single gene found in several unrelated plants, called LEAFY, while the UC San Diego group worked exclusively with a gene identified in the mustard plant, called APETALA1.

“These same two genes--LEAFY and APETALA1--are probably the key developmental switches in most, if not all, flowering plants, but each plant uses those genes a little differently, developing different mechanisms for turning on those genes,” Yanofsky said.

Many factors work together to tell a plant when it is time to flower, including the amount of food and water available, light, temperature and a plant’s age. Just how a plant senses many of these things remains a puzzle, but the latest discovery offers the key, experts said.

The LEAFY gene appears to be an ancient actor in the plant kingdom. Its function is to trigger any one of a large number of variations of the APETALA1 gene found in different plants, the researchers said.

Working in tandem, the genes initiate a cascade of thousands of genetic changes that result in the precisely defined whorls and colored petals of a flower.

“Somewhat to our surprise, either gene is sufficient to convert shoots into flowers,” Weigel said.

The Salk team has already patented its discovery. Its gene may find more commercial applications because it seems to be easier to identify in different flowering plants and therefore is not as hard to isolate.

Scientists suspect that the LEAFY gene may have appeared very early in the evolution of plants. It is possible it may be the universal trigger for the formation of reproductive structures in even the most primitive ferns and lichens, they said.

They currently are testing the effect of the gene in spruce trees in the hope that they can accelerate the formation of seed cones in a conifer.