Rhodopsin is a light receptor comprised of an opsin protein and a light-sensitive retinal chromophore. Despite more than a century of scrutiny, there is no evidence that opsins function in chemosensation. Here, we demonstrate that three Drosophila opsins, Rh1, Rh4, and Rh7, are needed in gustatory receptor neurons to sense a plant-derived bitter compound, aristolochic acid (ARI). The gustatory requirements for these opsins are light-independent and do not require retinal. The opsins enabled flies to detect lower concentrations of aristolochic acid by initiating an amplification cascade that includes a G-protein, phospholipase Cβ, and the TRP channel, TRPA1. In contrast, responses to higher levels of the bitter compound were mediated through direct activation of TRPA1. Our study reveals roles for opsins in chemosensation and raise questions concerning the original roles for these classical G-protein-coupled receptors.
Bibliographical noteFunding Information:
We thank Wesley Kroeze and Bryan Roth for providing HTLA cells and guidance for the TANGO assay, and Chao Liu for conducting preliminary studies. N.Y.L. was partially supported by a predoctoral fellowship from the National Eye Institute ( F31EY027191 ). M.Y.N. received an Israel Science Foundation grant ( 494/16 ). This work was supported by grants to CM from the National Institute on Deafness and Other Communication Disorders ( DC007864 and DC016278 ).
© 2020 The Author(s)
- TRP channel
- phospholipase C