The molecular basis for water taste in Drosophila

The detection of water and the regulation of water intake are essential for animals to maintain proper osmotic homeostasis1. Drosophila and other insects have gustatory sensory neurons that mediate the recognition of external water sources2-4, but little is known about the underlying molecular mechanism for water taste detection. Here, we identify a member of the Degenerin/Epithelial Sodium Channel family5, ppk28, as an osmosensitive ion channel that mediates the cellular and behavioral response to water. We use molecular, cellular, calcium imaging and electrophysiological approaches to show that ppk28 is expressed in water-sensing neurons and loss of ppk28 abolishes water sensitivity. Moreover, ectopic expression of ppk28 confers water sensitivity to bitter-sensing gustatory neurons in the fly and sensitivity to hypo-osmotic solutions when expressed in heterologous cells. These studies link an osmosensitive ion channel to water taste detection and drinking behavior, providing the framework for examining the molecular basis for water detection in other animals.