Another Example of Convergent Biochemical Evolution: Caffeine
Sometimes I feel a bit like an odd-man-out living in Seattle, the coffee house capital of the U.S., because I don't like coffee. Don't get me wrong -- I'm no saint when it comes to caffeine. I just prefer to obtain the chemical through other means: I love tea (I've never tried a tea I didn't like), and I'm also a lifelong
addict connoisseur of that sweet intelligently designed nectar known as Mountain Dew. (Here's a shot of a shelf in my office sporting a small basalt column and two bottles of Dew.) But have you ever wondered why there other means of imbibing caffeine - i.e., why are there multiple types of (natural) caffeinated beverages? Coffee is derived from plants of the genus Coffea which belong to the order Gentianales, whereas most popular teas are derived from the plant Camellia sinensis of the order Ericales. And then of course caffeine is also found in beans of the cacao tree (order Malvales), which are used to produce chocolate. How is it that each of these plants came to naturally produce caffeine? After sequencing the "coffee genome," some biologists have now investigated this question, and they found that -- you guessed it - caffeine is another example of "convergent" biochemical evolution. According a recent article in Nature news, "Coffee got its buzz by a different route than tea":
Caffeine's buzz is so nice it evolved twice. The coffee genome has now been published, and it reveals that the coffee plant makes caffeine using a different set of genes from those found in tea, cacao and other perk-you-up plants.The original study published in Science, "The coffee genome provides insight into the convergent evolution of caffeine biosynthesis," puts it this way:
When the team looked for gene families that distinguish coffee from other plants, those that make caffeine topped the list. The genes encode methyltransferase enzymes, which transform a xanthosine molecule into caffeine by adding methyl chemical groups in three steps. Tea and cacao, meanwhile, make caffeine using different methyltransferases from those the team identified in robusta. 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, Albert says.
These results highlight the distinct acquisition of caffeine biosynthesis in the coffee plant, providing an example of convergent evolution of secondary metabolic pathways encoded by tandemly duplicated genes.They propose that there were at least two (and maybe three) instances of the origin of caffeine production:
Caffeine biosynthetic NMTs [N-methyltransferases] from coffee nested within a gene clade distinct from those of cacao or tea, which group together as sister lineages. Thus, a minimum of two independent origins of caffeine biosynthetic NMT activity can be inferredConvergent biochemical evolution? Sounds like a candidate for explanation via common design to me.