Functional Characterization of Inositol Pyrophosphates in Arabidopsis thaliana

Diphosphorylated inositol polyphosphates, also termed inositol pyrophosphates, are important energy-rich molecules that regulate many crucial molecular events in different eukaryotic organisms. In mammals and fungi, two distinct classes of inositol polyphosphate kinases mediate their biosynthesis: Kcs1/IP6K- and Vip1/PPIP5K-like proteins. Even though inositol polyphosphate molecules more polar than InsP6 have been detected in some plant species, their synthesis, isomer identity and most importantly, their physiological functions have not yet been addressed. The present work reports that PPIP5K homologs are widely distributed in plants and that Arabidopsis VIH1 and VIH2 are functional PPIP5K enzymes. This study provides evidence that jasmonate specifically induces the inositol pyrophosphate InsP8 and that both steady state and jasmonate-induced levels of InsP8 depend on VIH2. Analyses of vih2 loss of function lines, in silico docking experiments and in vitro radioligand binding-based reconstitution assays suggest that InsP8 is a critical co-factor of the ASK1-COI1-JAZ jasmonate coreceptor complex and plays important roles in the plant defense against insect herbivores and necrotrophic fungi. The obtained data show furthermore that the F-box component COI1 determines the inositol polyphosphate binding specificity of the jasmonate receptor and suggest that coincidence detection of two unrelated ligands, jasmonate and inositol pyrophosphate, is critical for hormone perception.