A GENE ENCODING PHOSPHATIDYLINOSITOL-4-PHOSPHATE 5-KINASE IS INDUCED BY WATER-STRESS AND ABSCISIC-ACID IN ARABIDOPSIS-THALIANA

Phosphatidylinositol-4-phosphate 5-kinase (PIP5K) phosphorylates phosp hatidylinositol-4-phosphate to produce phosphatidylinositol-4,5-bispho sphate as a precursor of two second messengers, inositol-1,4,5-triphos phate and diacylglycerol, and as a regulator of many cellular proteins involved in signal transduction and cytoskeletal organization. Despit e PIP5K playing such an essential role in a number of physiological pr ocesses, much still remains to be made clear about its association wit h plants. Searching the Arabidopsis expression sequence tag database a gainst already known yeast and mammalian PIP5K cDNAs, we identified tw o clones which partly encode the same Arabidopsis PIP5K and isolated a corresponding full-length cDNA encoding a protein that we designated AtPIP5K1. Recombinant AtPIP5K1 expressed in Escherichia coil possessed a PIP5K activity in vitro. Due to some structural and biochemical dif ferences, AtPIP5K1 was not categorized as either a type I or type II P IP5K. The expression of the AtPIP5K1 mRNA was induced rapidly by treat ing Arabidopsis plants with drought, salt and abscisic acid, which sug gests that AtPIP5K1 is involved in water-stress signal transduction. T hese data give evidence for a close link between phosphoinositide sign aling cascades and water-stress responses in plants.