Cloning of Arabidopsis thaliana phosphatidylinositol synthase and functional expression in the yeast pis mutant

It is believed that phosphatidylinositol (PI) metabolism plays a central role in signalling pathways in both animals and higher plants. PI is synthesized from CDP-diacylglycerol (CDP-DG) and myo-inositol by phosphatidylinositol synthase (PI synthase, EC 2.7.8.11). Here we report the identification of a plant cDNA (AtPIS1) encoding a 26 kDa PI synthase from Arabidopsis thaliana. The plant enzyme as deduced from its cDNA sequence shares 35–41% identical amino acids with PI synthases from Saccharomyces cerevisiae and mammals. AtPIS1 functionally complements a mutant of S. cerevisiae with a lesion in PI synthase, and recombinant AtPIS1 protein present in yeast membranes strongly depends on the two principal substrates, myo-inositol and CDP-DG, and requires Mg²⁺ ions for full activity.