Arabidopsis ITPK1 and ITPK2 Havean Evolutionarily Conserved Phytic Acid Kinase Activity

Diphospho-myo-inositol polyphosphates, also termed inositol pyrophosphates, are molecular messengers containing at least one high-energy phosphoanhydride bond and regulate a wide range of cellular processes in eukaryotes. While inositol pyrophosphates InsP7 and InsP8 are present in different plant species, both the identity of enzymes responsible for InsP7 synthesis and the isomer identity of plant InsP7 remain unknown. This study demonstrates that Arabidopsis ITPK1 and ITPK2 catalyze the phosphorylation of phytic acid (InsP6) to the symmetric InsP7 isomer 5-InsP7 and that InsP6 kinase activity of ITPK enzymes is evolutionarily conserved from humans to plants. We also show by 31P NMR that plant InsP7 is structurally identical to the in vitro InsP6 kinase products of ITPK1 and ITPK2. Our findings lay the biochemical and genetic basis to uncover physiological processes regulated by 5-InsP7 in plants.