Lipid phosphate phosphatases in Arabidopsis - Regulation of the AtLPP1 gene in response to stress

An Arabidopsis thaliana gene (AtLPP1) was isolated on the basis that it was transiently induced by ionizing radiation. The putative AtLPP1 gene produc t showed homology to the yeast and mammalian lipid phosphate phosphatase en zymes and possessed a phosphatase sig nature sequence motif. Heterologous e xpression and biochemical characterization of the AtLPP1 gene in yeast show ed that it encoded an enzyme (AtLpp1p) that exhibited both diacylglycerol p yrophosphate phosphatase and phosphatidate phosphatase activities. Kinetic analysis indicated that diacylglycerol pyrophosphate was the preferred subs trate for AtLpp1p in vitro. A second Arabidopsis gene (AtLPP2) was identifi ed based on sequence homology to AtLPP1 that was also heterologously expres sed in yeast. The AtLpp2p enzyme also utilized diacylglycerol pyrophosphate and phosphatidate but with no preference for either substrate. The AtLpp1p and AtLpp2p enzymes showed differences in their apparent affinities for di acylglycerol pyrophosphate and phosphatidate as well as other enzymological properties. Northern blot analyses showed that the AtLPP1 gene was prefere ntially expressed in leaves and roots, whereas the AtLPP2 gene was expresse d in all tissues examined. AtLPP2, but not AtLPP2, was regulated in respons e to various stress conditions. The AtLPP1 gene was transiently induced by genotoxic stress (gamma ray or UV-B) and elicitor treatments with mastopara n and harpin. The regulation of the AtLPP1 gene in response to stress was c onsistent with the hypothesis that its encoded lipid phosphate phosphatase enzyme may attenuate the signaling functions of phosphatidate and/or diacyl glycerol pyrophosphate that form in response to stress in plants.