Molecular and Biochemical Characterization of Three WD-Repeat-Domain-containing Inositol Polyphosphate 5-Phosphatases in Arabidopsis thaliana

Type II inositol polyphosphate 5-phosphatases (5PTases) in animals and yeast have been known to be important for regulating inositol and phospholipid signaling by hydrolyzing phosphate from both inositol polyphosphates and phosphoinositides. However, the molecular and biochemical properties of type II 5PTases in plants have not yet been studied. In this report, we show that three Arabidopsis genes, At5PTasel2, At5PTasel3 and At5PTasel4, encode proteins with a 5PTase domain and a WD-repeat domain, a novel combination present only in plant 5PTases. We demonstrate that these genes are differentially expressed in Arabidopsis organs and At5PTasel3 is induced in response to ABA and wounding treatments. Our biochemical studies reveal that although both At5PTasel2 and At5PTasel3 exhibit phosphatase activity toward only Ins(1,4,5)P 3 , At5PTasel4 hydrolyzes phosphate from PI(4,5)P 2 , PI(3,4,5)P 3 and Ins(1,4,5)P 3 with the highest substrate affinity toward PI(4,5)P 2 . All three At5PTases require Mg 2 + for their phosphatase activities. Our molecular and biochemical characterization of three WD-repeat-domain-containing At5PTases provides a foundation for further elucidation of their cellular functions in Arabidopsis.