What genes in genome of the tree shrew allow it to eat very spicy food ???

Recently these GEITP pages discussed the koala genome, including discovery of an “evolutionary bloom, resulting in 31 genes” in the CYP2C subfamily (compared to just four CYP2C genes in human and 15 Cyp2c genes in mouse); it was speculated that one or more of these additional CYP2C enzymes are likely able to metabolize eucalyptus plants which are the main dietary component for the koala, whereas most eucalyptus is too toxic for most animals. There are many other examples of a plant being noxious to almost all animals, while a particular species thrives on that plant. The plant genus Capsicum is an example –– and the topic herein [see attached article].

Capsicum includes 22 wild species and produces a capsaicinoid called capsaicin, which we all know is VERY spicy hot..!! One of these species, the chili pepper, is a low shrub with capsaicin-containing fruits that are readily accessible to mammals and birds. However, capsaicinoids in these plants repel most animals by evoking a sharp and burning sensation through activation of the nociceptor, transient receptor potential vanilloid type-1 (TRPV1) ion channel. Interestingly, birds are an exception –– due to two specific point mutations in their TRPV1 channel gene that render them insensitive to capsaicin. This environmental adaptation broadens the range of diet in birds and also confers an advantage to the plant, because their seeds can be widely distributed by the birds.

Humans have an acute sensitivity to spicy food, and many find it unbearable; even so, with training, some have learned to enjoy the burning sensation elicited by consuming spicy food –– which might even confer protection against bacterial and fungal infection in the human gut. The tree shrew is a mammal closely related to primates. Authors [see attached paper] found that tree shrews actively feed on chili pepper, when it is provided to them. By whole-genome sequencing (WGS) analysis, authors identified a nucleotide alteration resulting in an amino acid change in the tree shrew TRPV1 gene, and they show that this change renders the TRPV1 channel refractory to capsaicinoid-induced activation.

Moreover, authors discovered that Piper boehmeriaefolium, another spicy plant that overlaps geographically with the ecological niche of the tree shrew, produces Cap2, a capsaicin analog, in abundance. Authors propose that there is a strong selection for the tree shrew TRPV1 gene mutation that might be the result of environmental pressure for positive selection, i.e. part of an evolutionary adaptation mechanism that enables the tree shrew to tolerate pungency –– thus widening the range of its diet for better survival advantage.

PLoS Biol July 2o18; 16: e2004921

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