<i>Arabidopsis</i> PFA-DSP-Type Phosphohydrolases Target Specific Inositol Pyrophosphate Messengers

Abstract

Inositol pyrophosphates are signaling molecules containing at least one phosphoanhydride bond that regulate a wide range of cellular processes in eukaryotes. With a cyclic array of phosphate esters and diphosphate groups around <i>myo</i>-inositol, these molecular messengers possess the highest charge density found in nature. Recent work deciphering inositol pyrophosphate biosynthesis in <i>Arabidopsis</i> revealed important functions of these messengers in nutrient sensing, hormone signaling, and plant immunity. However, despite the rapid hydrolysis of these molecules in plant extracts, very little is known about the molecular identity of the phosphohydrolases that convert these messengers back to their inositol polyphosphate precursors. Here, we investigate whether <i>Arabidopsis</i> Plant and Fungi Atypical Dual Specificity Phosphatases (PFA-DSP1-5) catalyze inositol pyrophosphate phosphohydrolase activity. We find that recombinant proteins of all five <i>Arabidopsis</i> PFA-DSP homologues display phosphohydrolase activity with a high specificity for the 5-β-phosphate of inositol pyrophosphates and only minor activity against the β-phosphates of 4-InsP₇ and 6-InsP₇. We further show that heterologous expression of <i>Arabidopsis</i> PFA-DSP1-5 rescues wortmannin sensitivity and deranged inositol pyrophosphate homeostasis caused by the deficiency of the PFA-DSP-type inositol pyrophosphate phosphohydrolase Siw14 in yeast. Heterologous expression in <i>Nicotiana benthamiana</i> leaves provided evidence that <i>Arabidopsis</i> PFA-DSP1 also displays 5-β-phosphate-specific inositol pyrophosphate phosphohydrolase activity <i>in planta</i>. Our findings lay the biochemical basis and provide the genetic tools to uncover the roles of inositol pyrophosphates in plant physiology and plant development.