Gene find could yield decaffeinated plants

An international team has succeeded in cloning one of tea’s genes for making caffeine—a step toward creating decaf tea and coffee plants.

The gene, TCS1, codes for caffeine synthase, the enzyme that controls the final two steps in the molecule’s four-step synthesis, explain Misako Kato and Hiroshi Ashihara of Ochanomizu University in Tokyo and their colleagues in the Aug. 31 Nature. When the researchers finally cloned TCS1, they found it had little similarity to other genes.

Important as caffeine has been to humanity—inspiring cuisine, commerce, and poetry, not to mention preventing the collapse of the industrialized world on Monday mornings—biologists have only recently begun unraveling nature’s own caffeine synthesis.

Some 40 species of plants make caffeine, but “no function is really known” for the chemical, notes coauthor Alan Crozier of the University of Glasgow in Scotland. He acknowledges the theories that caffeine might repel pests or build up in soil to sabotage seeds from rival plants.

However, he objects, “there are naturally low-caffeine plants that grow quite happily.”

Decaf now amounts to about 20 percent and 8 percent of the total U.S. coffee and tea markets, respectively, Crozier notes. “To someone like me who likes good, strong [coffee], decaffeinated tastes like dishwater,” he grumbles.

Coffee and tea plants become caffeinated by virtually the same chemistry, Crozier says. Finding the right gene to switch off in either plant could create full-flavor beverages without caffeine.

The report in Nature ranks as the first published report of a gene associated with the synthesis of caffeine in tea, Crozier claims. He says published because not everything on caffeine gets into print. The field isn’t exactly boiling. Funding is scarce and the number of labs known to be working in the field may be as small as three. Yet in June, the University of Hawaii in Honolulu received U.S. patent 6,075,184, involving a caffeine-synthesis gene in coffee. The gene sequence in the patent “is nothing like ours,” Crozier comments.

The Hawaiian biologists whose work led to the patent discussed findings in places with lower profiles than Nature: ACTA Horticulture and a 1999 coffee conference.

In the Tokyo-Glasgow collaboration, “the real donkey work and the part where no one thought we were getting anywhere was the 6 or 7 years of trying to purify enough enzyme to work with,” Crozier recalls. Last year, when the researchers determined caffeine synthase’s amino acid sequence, they then were able to create molecular probes for finding the gene encoding the enzyme.

To see whether they’d ferreted out the right gene, the researchers inserted it into Escherichia coli bacteria, which they fed precursors for caffeine. Bacteria with the new gene could pump out caffeine, but unmodified bacteria couldn’t.

John Stiles, one of the biologists behind the patent and now at the biotech firm Integrated Coffee Technologies in Honolulu, speaks admiringly of the Tokyo-Glasgow team’s triumph: “It was certainly a really good feat to purify that enzyme.”

Stiles says his patented enzyme controls an earlier step in the synthesis than the gene reported in the Nature paper. By modifying the patented gene in plants, he hopes to avoid creating plants that build up half-finished caffeine, in the form of a chemical called 7-methylxanthine, which would require research on its potential effects on consumers.

Stiles already has coffee plants growing, but he can’t yet say how things will turn out. William Franke, vice president of scientific and regulatory affairs for Lipton in Englewood, Calif., says the company’s current tea-decaffeinating process is “safe and effective.” But he says if someone finds a good alternative, he’ll take a look.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.