Hot peppers gain spice through duplication

I’m a pretty big fan of spicy food and hot peppers, but I’ll be honest and admit that I didn’t know much about the genomics of organisms which give rise to the flavor. So it was neat to see that Nature Genetics has an open access paper on the topic, Genome sequence of the hot pepper provides insights into the evolution of pungency in Capsicum species. Lots of new information to me in the publication. For example it seems that hot peppers have a genome on the same order of size as that of humans (and therefore most tetrapods). This is contrast to a model plant such as Arabidopsis thaliana, which is much smaller. Most of the genome consists of repetitive elements, not to surprising among eukaryotes. And the number of genes is estimated to be north of 30,000, so somewhat more than humans, but in the same range. Because peppers are Solanaceae there are excellent genomic resources to compare it with, tomato and potoato (and with nearly 200× coverage I’m assuming the assembly was OK).

The big question that they seemed to want to answer was the nature of the capsaicin biosynthesis pathway. Basically what makes peppers spicy (the posited functional reason for spiciness is that it discourages mammal consumption, but encourages birds, who are much better at scattering seeds because they fly). The conclusion the authors come to is that particular genes implicated in this function exhibit both elevated gene expression and duplication in relation to Solanaceae outgroups. This seems plausible enough, and suggests that spiciness is just a ramping up of a flavor which is present at some lower basal fraction. Why it might be useful to know which loci are implicated in spiciness is pretty obvious.

Citation: Nature Genetics (2014) doi:10.1038/ng.2877

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