A clade of receptor-like cytoplasmic kinases and 14-3-3 proteins coordinate inositol hexaphosphate accumulation

Abstract Inositol hexaphosphate (InsP 6 ) is the major storage form of phosphorus in seeds. Reducing seed InsP 6 content is a breeding objective in agriculture, as InsP 6 negatively impacts animal nutrition and the environment. Nevertheless, how InsP 6 accumulation is regulated remains largely unknown. Here, we identify a clade of receptor-like cytoplasmic kinases (RLCKs), named Inositol Polyphosphate-related Cytoplasmic Kinases 1-6 (IPCK1-IPCK6), deeply involved in InsP 6 accumulation. The InsP 6 concentration is dramatically reduced in seeds of ipck quadruple ( T-4m / C-4m ) and quintuple ( C-5m ) mutants, accompanied with the obviously increase of phosphate (Pi) concentration. The plasma membrane-localized IPCKs recruit IPK1 involved in InsP 6 synthesis, and facilitate its binding and activity via phosphorylation of GRF 14-3-3 proteins. IPCKs also recruit IPK2s and PI-PLCs required for InsP 4 /InsP 5 and InsP 3 biosynthesis respectively, to form a potential IPCK-GRF-PLC-IPK2-IPK1 complex. Our findings therefore uncover a regulatory mechanism of InsP 6 accumulation governed by IPCKs, shedding light on the mechanisms of InsP biosynthesis in eukaryotes.