Acts on phosphatidylinositol (PtdIns) in the first committed step in the production of the second messenger inositol-1,4,5-trisphosphate. Necessary for proper organization of the trans-Golgi network (TGN) and post-Golgi secretion in root hairs. Together with PI4KB2, required during polarized root hair expansion and pollen tube elongation. Functions redundantly with PI4KB2 upstream of the cold response phosphoinositide-dependent phospholipase C (PI-PLC) pathway. a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol) + ATP = a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol 4-phosphate) + ADP + H(+) Stimulated by phosphatidylinositol 4-phosphate (PtdIns4P). Slightly repressed by phosphatidyl-choline (PtdCho), wortmannin and adenosine. Interacts with AHK2, CBL1 and RABA4D. Associated to tip-localized membranes in growing root hairs. Expressed constitutively in leaves, roots, flowers, and stems. The PPC (Plant PI4K Charged) region is involved in membrane targeting and phospholipid binding. When associated with PI4KB2 disruption: aberrant root hair morphologies, and short and wavy pollen tubes. Belongs to the PI3/PI4-kinase family. Type III PI4K subfamily.