<i>Drosophila</i> Fatty Acid Taste Signals through the PLC Pathway in Sugar-Sensing Neurons

<div><p>Taste is the primary sensory system for detecting food quality and palatability. <i>Drosophila</i> detects five distinct taste modalities that include sweet, bitter, salt, water, and the taste of carbonation. Of these, sweet-sensing neurons appear to have utility for the detection of nutritionally rich food while bitter-sensing neurons signal toxicity and confer repulsion. Growing evidence in mammals suggests that taste for fatty acids (FAs) signals the presence of dietary lipids and promotes feeding. While flies appear to be attracted to fatty acids, the neural basis for fatty acid detection and attraction are unclear. Here, we demonstrate that a range of FAs are detected by the fly gustatory system and elicit a robust feeding response. Flies lacking olfactory organs respond robustly to FAs, confirming that FA attraction is mediated through the gustatory system. Furthermore, flies detect FAs independent of pH, suggesting the molecular basis for FA taste is not due to acidity. We show that low and medium concentrations of FAs serve as an appetitive signal and they are detected exclusively through the same subset of neurons that sense appetitive sweet substances, including most sugars. In mammals, taste perception of sweet and bitter substances is dependent on phospholipase C (PLC) signaling in specialized taste buds. We find that flies mutant for <i>norpA</i>, a <i>Drosophila</i> ortholog of PLC, fail to respond to FAs. Intriguingly, <i>norpA</i> mutants respond normally to other tastants, including sucrose and yeast. The defect of <i>norpA</i> mutants can be rescued by selectively restoring <i>norpA</i> expression in sweet-sensing neurons, corroborating that FAs signal through sweet-sensing neurons, and suggesting PLC signaling in the gustatory system is specifically involved in FA taste. Taken together, these findings reveal that PLC function in <i>Drosophila</i> sweet-sensing neurons is a conserved molecular signaling pathway that confers attraction to fatty acids.</p>