Phosphatidic acid: an emerging plant lipid second messenger

Evidence is accumulating that phosphatidic acid is a second messenger. Its level increases within minutes of a wide variety of stress treatments including ethylene, wounding, pathogen elicitors, osmotic and oxidative stress, and abscisic acid. Enhanced signal levels are rapidly attenuated by phosphorylating phosphatidic acid to diacylglycerol pyrophosphate. Phosphatidic acid is the product of two signalling pathways, those of phospholipases C and D, the former in combination with diacylglycerol kinase. Families of these genes are now being cloned from plants. Several downstream targets of phosphatidic acid have been identified, including protein kinases and ion channels.