Convergent Caffeine

Richard Mark Glover
 Cacao pods from the Dominican Republic
Cacao pods from the Dominican Republic
(Courier Photo:Richard Mark Glover)

Caffeine, that indispensable morning drug many of us can’t do without, was the object of an experiment chronicled in the journal Nature last week. Scientists completed and published for the first time the genome of coffea canephora also known as coffea robusta, enabling a full analysis of how caffeine in coffea robusta evolved.

The international team of scientists identified over 25,000 protein-making genes in the coffea robusta DNA chain and compared it with cacao and tea, also caffeine producing plants.

Although there are similarities in the plants evolutionary paths, the catalysts producing caffeine in cacao and tea did not evolve from the same lineage as coffee.

“Tea and cacao, meanwhile, make caffeine using different methyltransferases from those the team identified in robusta,”wrote Ewen Callaway in Nature. “This suggests that the ability to make caffeine evolved at least twice, in the ancestor of coffee plants and in a common ancestor of tea and cacao.”

Biologists call this convergent evolution – ending with the same chemical compounds - via different paths.

“They’re all descendants of a common ancestor enzyme that started screwing around with xanthosine compounds,” said Victor A Albert, an evolutionary biologist at the University of Buffalo and a lead scientist in the study.

Along the coffee plant’s evolutionary pathway, xanthosine, a nucleoside, and an enzyme known as N-methyltransferases, provided the biological engine for the metabolic change that produced caffeine in robusta. Catalyzing chemical reactions prompted within the cell by enzymes like N-methyltransferases, often produce chemical weapons the plant uses against other plant competitors.

“When coffee leaves fall to the ground, they contaminate the soil with caffeine, which makes it difficult for other plants to germinate. Coffee may thus use caffeine to kill off the competition,” wrote Carl Zimmer of the New York Times. “Coffee plants also use caffeine to ward off insects that would otherwise feast on their leaves and beans. But coffee…also lace their nectar with low doses of caffeine and in that form it seems to benefit the plants in a different way.”

And most of us know that caffeine sweet spot.

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