View Program - 63rd Annual Drosophila Research Conference

Drosophila melanogaster use their sense of taste to forage for food, avoid toxic or hazardous substances, to select partners for courtship and mating and to choose suitable oviposition sites. Although the cellular and molecular basis of sweet, bitter and salt tastes have been well characterized in flies a detailed understanding of how they sense acid is lacking. Based on past studies, members of Gustatory Receptor (GR) or Ionotropic Receptor (IR) families are unlikely to function broadly as acid receptors. Hence, we elected to test whether fly genes that are distantly related to mammalian Otop1, a proton channel required for sour taste in mammals, are required for acid taste in flies. RNAi-mediated silencing as well as CRISPR/Cas9-mediated mutagenesis of OtopLA, but not of OtopLB or of OtopLC caused a severe reduction in behavioral aversion to sweet solutions in the presence of low pH or high concentrations of carboxylic acids as well as action potentials induced by acids on neurons in labellar taste bristles. We identified a novel OtopLA isoform from the proboscis (OtopLAp)that rescued the behavioral deficit as well as the reduced neuronal sensitivity to acids exhibited by the OtopLA mutant. Although high concentrations of HCl caused behavioral aversion, we observed mild attraction to low concentrations of HCl. This attraction was also impaired in OtopLA mutant. By conducting cell-type specific genetic rescue experiments in various subsets of taste neurons, we demonstrated that OtopLA functions in different neuronal subsets to cause different behavioral outcomes. This study demonstrates functional conservation of a taste receptor between flies and mammals. It also elucidates that the same taste receptor is required both for appetitive and repulsive gustatory behaviors.

Cellular and molecular basis of detection of acidic pH in fly gustatory system