Amino acids activate parallel chemosensory pathways in Drosophila

Amino acids (AAs) are essential dietary macronutrients that impact an organism's fitness in a concentration-dependent manner, but the mechanisms mediating AA detection to drive consumption are less clear. In Drosophila, we identified the full repertoire of taste cells and receptors involved in feeding initiation towards a glutamate-rich AA mixture, tryptone, using in vivo calcium imaging and the proboscis extension response (PER). We found that AA attraction occurs through sweet cells, whereas feeding aversion is mediated through Ionotropic Receptor 94e (IR94e) cells and bitter cells, dependent on concentration. Further, our results corroborate previous findings that ionotropic receptors IR76b, IR51b, and IR94e detect AAs in their respective cell types. Additionally, we describe a new role for the appetitive IR56d receptor and bitter gustatory receptors in detecting AAs. This work establishes a cellular and molecular framework of AA feeding initiation and highlights redundancy in aversive pathways that regulate AA feeding.