Characterization of odorant receptors from a non-ditrysian moth, <i>Eriocrania semipurpurella</i> sheds light on the origin of the sex pheromone receptors in Lepidoptera

Abstract:
Pheromone receptors (PRs) are essential in moths to detect sex pheromones for mate finding. However, it remains
unknown from which ancestral proteins these specialized receptors arose. The oldest lineages of moths, so-called
non-ditrysian moths, use short-chain pheromone components, secondary alcohols, or ketones, so called Type 0 pheromones
that are similar to many common plant volatiles. It is, therefore, possible that receptors for these ancestral
pheromones evolved from receptors detecting plant volatiles. Hence, we identified the odorant receptors (ORs) from a
non-ditrysian moth, Eriocrania semipurpurella (Eriocraniidae, Lepidoptera), and performed functional characterization
of ORs using HEK293 cells. We report the first receptors that respond to Type 0 pheromone compounds; EsemOR3
displayed highest sensitivity toward (2S, 6Z)-6-nonen-2-ol, whereas EsemOR5 was most sensitive to the behavioral
antagonist (Z)-6-nonen-2-one. These receptors also respond to plant volatiles of similar chemical structures, but with
lower sensitivity. Phylogenetically, EsemOR3 and EsemOR5 group with a plant volatile-responding receptor from the
tortricid moth Epiphyas postvittana (EposOR3), which together reside outside the previously defined lepidopteran PR
clade that contains the PRs from more derived lepidopteran families. In addition, one receptor (EsemOR1) that falls at
the base of the lepidopteran PR clade, responded specifically to b-caryophyllene and not to any other additional plant or
pheromone compounds. Our results suggest that PRs for Type 0 pheromones have evolved from ORs that detect
structurally-related plant volatiles. They are unrelated to PRs detecting pheromones inmore derived Lepidoptera, which,
in turn, also independently may have evolved a novel function from ORs detecting plant volatiles.