Regulation of phototransduction responsiveness and retinal degeneration by a phospholipase D-generated signaling lipid

Drosophila melanogaster phototransduction proceeds via a phospholipase C (PLC)-triggered cascade of phosphatidylinositol (PI) lipid modifications, many steps of which remain undefined. We describe the involvement of the lipid phosphatidic acid and the enzyme that generates it, phospholipase D (Pld), in this process. Pld^null flies exhibit decreased light sensitivity as well as a heightened susceptibility to retinal degeneration. Pld overexpression rescues flies lacking PLC from light-induced, metarhodopsin-mediated degeneration and restores visual signaling in flies lacking the Pl transfer protein, which is a key player in the replenishment of the Pl 4,5-bisphosphate (PlP₂) substrate used by PLC to transduce light stimuli into neurological signals. Altogether, these findings suggest that Pld facilitates phototransduction by maintaining adequate levels of PlP₂ and by protecting the visual system from metarhodopsin-induced, low light degeneration.