A Molecular and Cellular Context-Dependent Role for Ir76b in Detection of Amino Acid Taste

Amino acid taste is expected to be a universal property among animals. Although sweet, bitter, salt, and water tastes have been well characterized in insects, the mechanisms underlying amino acid taste remain elusive. From a Drosophila RNAi screen, we identify an ionotropic receptor, Ir76b, as necessary for yeast preference. Using calcium imaging, we identify Ir76b+ amino acid taste neurons in legs, overlapping partially with sweet neurons but not those that sense other tastants. Ir76b mutants have reduced responses to amino acids, which are rescued by transgenic expression of Ir76b and a mosquito ortholog AgIr76b. Co-expression of Ir20a with Ir76b is sufficient for conferring amino acid responses in sweet-taste neurons. Notably, Ir20a also serves to block salt response of Ir76b. Our study establishes the role of a highly conserved receptor in amino acid taste and suggests a mechanism for mutually exclusive roles of Ir76b in salt- and amino-acid-sensing neurons. [Display omitted] •Drosophila females display amino acid feeding preference after mating•Taste neurons in female tarsi are activated by amino acids•A highly conserved receptor, Ir76b, is required for amino acid taste•Ir20a mediates amino acid taste and blocks salt taste dependent on Ir76b Ganguly et al. demonstrate that Ir76b mediates cellular and behavioral responses to amino acids that underlie post-mating yeast and amino acid feeding preferences of Drosophila females. Ir20a, possibly one among many factors, plays a role in changing Ir76b activity from an ungated salt receptor to an amino-acid-gated receptor.