Gene Helps Plants Weather Cold

Scientists have engineered a small mustardlike plant to withstand the damaging effects of freezing temperatures. The feat, reported in tomorrow's issue of Science, might someday allow farmers to rest easy when a sudden freeze sets in.

Many plants are equipped with proteins that enable them to tolerate cold weather. Some of these proteins seem to protect against dehydration and shriveling by filling the space between a plant's cell membrane and its tough cell wall. Partly because plants have many of these genes, however, researchers are worried that transferring just one gene wouldn't do much for improving cold tolerance.

In 1994, three teams made a discovery that pointed to a possible solution. They found that several cold-regulated (COR) genes all carry the same regulatory sequences--suggesting they are all turned on by the same signal when the mercury drops. Shortly thereafter, molecular geneticist Michael Thomashow of Michigan State University in East Lansing and his colleagues identified that signal: a transcription factor called CBF1.

In the current work, the Thomashow team attached the CBF1 gene to a regulatory sequence that ensures it will be active all the time. When they inserted the modified gene into Arabidopsis plants, the transgenic plants began producing the COR proteins even in warm temperatures. Experiments in which the researchers first froze and then thawed leaves from the modified plants showed "a dramatic enhancement in freezing tolerance," says Thomashow. What's more, plants could survive sudden temperature drops to as low as -8 degrees Celsius--4 degrees colder than the normal killing temperature for Arabidopsis.

The work "has profound implications for agriculture," says Charles Guy, a plant physiologist at the University of Florida in Gainesville. Crop plants that lack freezing tolerance, such as citrus, may be more difficult to modify than Arabidopsis because they may have lost all or part of their repertoire of cold tolerance genes. But, the experts say, making crops such as corn or soybeans even a little hardier could make a big difference in helping them weather cold snaps early or late in a growing season that cause the biggest crop losses.