If you’re anything like me, you responded to recent news articles on the global coffee and chocolate shortage with a wail. My own dismayed “Nooooo!” was just about fit for a Star Wars movie. I love coffee and chocolate, especially together: their rich color; their smoky, bitter, very lightly sweetened tastes; the caffeine… the caffeine.
I imagine chocolate coming from Europe and coffee coming from Seattle, but of course it wasn’t always that way. Though chocolate has a venerable place in European culture, it got there just five hundred years ago in the Columbian exchange; and any coffee aficionado worth their grounds can tell you that both Arabica and robusta beans are native to Ethiopia.
When plants full of the same psychoactive compound start turning up across oceans, you start to wonder when they evolved that compound, and why. And the plot thickens: caffeine is also found in tea, of course, not to mention the kola nut from Nigeria, and the yerba mate holly, guarana, and guayusa from the Amazon. If you’ve been keeping score, that’s three continents’ worth of caffeinated delights, and those are only the plants that humans consume.
Caffeine is what’s known among plant biologists as a specialized metabolite. It isn’t absolutely needed to keep the plant alive, but improves its chances a little; human addicts may feel the same effect. Plants synthesize caffeine mostly in seeds and nascent leaves, where the compound paralyzes pests that try and eat these vulnerable tissues. The caffeine molecule looks a great deal like the universally-used nucleotide (DNA component) adenosine, and it does its work both in the human brain and the insect physiology by impersonating adenosine’s energy-carrying cousin ATP.
Caffeine biosynthesis is a fairly simple pathway. Once you have adenosine around, which every organism known to science does, it’s just a matter of cutting one or two bonds and switching out a methyl group or two to generate caffeine. It’s the kind of metabolite that, if gene products were patents, would make you smack your forehead and shout, “Why didn’t I think of that first?!” Therefore it’s not surprising that caffeine biosynthesis has evolved at least twice in plants: they have plenty of enzymes that specialize in cutting bonds and transferring methyls, it was only a matter of time and slightly altered specificity. In fact, these researchers say, based on protein sequence analysis, that the same cutting-and-switching enzymes that held down one job in the plant left for the new caffeine-synthesis job several times in different plant lineages. So, although tea, coffee, and chocolate have the same delectable effects on our brains, they came to these effects independently.
Knowing this stuff won’t help us solve the caffeine shortage that is sure to give many of us metaphorical (and also withdrawal-induced) headaches over the next harvest season. Besides a sudden reversal of global climate change, it’s not clear what can do that. But at least we know that this precious metabolite is a feature of many plants, probably some we haven’t found yet. And if all else fails, there’s always straight-up pharmacological synthesis!