A phosphoinositide-specific phospholipase C pathway elicits stress-induced Ca2+ signals and confers salt tolerance to rice

In animal cells, phospholipase C (PLC) isoforms predominantly hydrolyze phosphatidylinositol- 4,5-biphosphates [PtdIns(4,5) P-2] into the second messengers diacylglycerol (DAG) and inositol 1,4,5-trisphosphate [Ins(1,4,5) P-3] to regulate diverse biological processes. By contrast, the molecular mechanisms and physiological significance of PLC signaling in plants still awaits full elucidation. Here, we identified a rice (Oryza sativa cv) PI-PLC, OsPLC1, which preferred to hydrolyze phosphatidylinositol-4-phosphate (PtdIns4P) and elicited stress-induced Ca2+ signals regulating salt tolerance. Analysis by ion chromatography revealed that the concentration of PtdIns4P was c. 28 times of that of PtdIns(4,5) P-2 in shoots. OsPLC1 not only converted PtdIns(4,5) P2 but also and even more efficiently - converted PtdIns4P into DAG and Ins(1,4,5) P-3 in vitro and in vivo. Salt stress induced the recruitment of OsPLC1 from cytoplasm to plasma membrane, where it hydrolyzed PtdIns4P. The stress-induced Ca2+ signaling was dependent on OsPLC1, and the PLC-mediated Ca2+ signaling was essential for controlling Na+ accumulation in leaf blades, thus establishing whole plant salt tolerance. Our work identifies a conversion pathway and physiological function for PtdIns4P pools in rice and reveals the connection between phosphoinositides and Ca2+ signals mediated by PLC during salt stress responses.