From Aspens to Artichokes, Genetics Breakthrough May Speed Up Breeding
USING genetic engineering, scientists have discovered a way to put flowering on fast-forward in a wide variety of plants.
From the lowly mustard weed to tomatoes and aspen trees, the technique could revolutionize commercial breeding of crops and ornamental plants, enhance tree reproduction, and serve as a powerful tool for studying plant genetics.
"This is very, very significant," says Andrew Bent, a plant geneticist at the University of Illinois at Urbana-Champaign. "For crops that have long generation times, this gives you an opportunity to speed up the flowering process," allowing breeders to modify a plant's characteristics at a much faster pace.
The discovery came as two research teams sought to activate one of two genes whose functions appeared to overlap.
One group, led by Detlef Weigel of the Salk Institute for Biological Studies in La Jolla, Calif., focused on a gene known as LEAFY. The other group, led by M. Alejandra Mandel at the University of California at San Diego, zeroed in on a gene called APETALA1. Both are present in a wide range of plant species.
Ordinarily, plant flowering responds to two broad triggers - environmental influences, such as day length and temperature, and an internal developmental "clock" that tracks growth time.
The mechanism for processing and sending this information to the rest of the plant is still poorly understood. But during the very early stages of flower formation, chemical signals activate the LEAFY and APETALA1 genes, as well as others, ensuring that nascent buds form flowers rather than shoots.
"We knew both genes were needed by plants to make flowers because mutant forms of these genes led to the formation of shoots, not flowers," Dr. Weigel says. "So, we asked the simple question: Is either gene enough to initiate flowering?"
TO answer the question, the researchers had to trick the genes into activating ahead of schedule. Through genetic engineering, the scientists developed mustard-like Arabidopsis plants whose LEAFY and APETALA1 genes respond to a chemical "promoter" from a cauliflower virus. The scientists then used the promoter to switch on the LEAFY and APETALA1 genes.
The activation of either LEAFY or APETALA1 gene was sufficient to induce flowering in the tiny plants. And the process took about one-third the time needed by normal Arabidopsis plants.
The Salk team also tested the approach on aspen trees, with dramatic results. Aspens generally don't begin to reproduce until they are from eight to 20 years old. By triggering the LEAFY gene, Weigel induced flowering in seven-month-old aspens.
Both teams, whose results are reported in the current issue of the journal Nature, are testing the technique on food crops such as corn, tomatoes, and rice. It could speed the introduction of new pest-or disease-resistant varieties. Over the longer term, some envision the precocious plants aiding growers in regions with short growing seasons.
Yet, some researchers note that the teams' technique reduces the number of flowers a plant produces, which could undercut yields. "In something like wheat, the crop is seeds, and the number of seeds is related to the number of flowers," says George Coupland, a plant geneticist at the Norwich Research Park in Britain.
This effect, however, could be an advantage in breeding unique ornamental plants. Although many of these applications may be a decade away, Dr. Bent says, he foresees the prospect of using the approach to breed trees such as poplar, cottonwood, or conifers for use in the paper and lumber industries.
"The problem with trees is that they most often are propagated by cuttings," Dr. Weigel adds. "This leads to little variation, making them more susceptible to pests or disease. By breeding, we can introduce variety to counteract that."
For ornamental plants, the technique could lead to new shapes for old varieties, aiding landscapers. Dr. Coupland, for instance, envisions snapdragons that have two or three large blossoms instead of clusters of flowers on the stalk. As for the next steps, "we need to analyze the regulatory sequences upstream of the LEAFY gene to understand how environmental factors induce flowering," says Elliot Meyerowitz, a biology professor at the California Institute of Technology in Pasadena, who is credited with pioneering the research into the LEAFY gene.