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Phosphatidylinositol-4-phosphate (PtdIns4P) is the most abundant phosphoinositide in plants and the precursor of phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P₂]. This lipid is the substrate of phosphoinositide-dependent phospholipase C (PI-PLC) that produces diacylglycerol (DAG) which can be phosphorylated to phosphatidic acid (PtdOH). In plants, it has been suggested that PtdIns4P may also be a direct substrate of PI-PLC. Whether PtdIns4P is the precursor of PtdIns(4,5)P₂ or a substrate of PI-PLC, its production by phosphatidylinositol-4-kinases (PI4Ks) is the first step in generating the phosphoinositides hydrolyzed by PI-PLC. PI4Ks can be divided into type-II and type-III. In plants, the identity of the PI4K upstream of PI-PLC is unknown. In Arabidopsis, cold triggers PI-PLC activation, resulting in PtdOH production which is paralleled by decreases in PtdIns4P and PtdIns(4,5)P₂. In suspension cells …