A number of repellent compounds produced by plants elicit a spicy or pungent sensation in mamm
als
1,
2,
3,
4,
5,
6,
7,
8,
9,
10,
11,
12,
13,
14,
15 and
16. In sever
al cases, this has been found to occur through activation of ion channels in the transient receptor potenti
al (TRP) family
1,
2,
3,
4,
5,
6 and
7. We report that isothiocyanate (ITC), the pungent ingredient of wasabi, is a repellent to the insect
Drosophila melanogaster, and that the
painless gene, previously known to be required for larv
al nociception, is required for this avoidance behavior. A
painless reporter gene is expressed in gustatory receptor neurons of the labi
al p
alpus, tarsus, and wing anterior margin, but not in olfactory receptor neurons, suggesting a gustatory role. Indeed,
painless expression overlaps with a variety of gustatory-receptor gene reporters. Some, such as Gr66a, are known to be expressed in neurons that mediate gustatory repulsion
8,
9 and
10.
painless mutants are not taste blind; they show norm
al aversive gustatory behavior with s
alt and quinine and attractive responses to sugars and capsaicin. The
painless gene is an evolutionary homolog of the mamm
alian “wasabi receptor” TRPA1/ANKTM1
[6],
also thought to be involved in nociception. Our results suggest that the stinging sensation of isothiocyanate is caused by activation of an evolutionarily conserved molecular pathway that is
also used for nociception.