Catalyzes the transfer of the phosphorylinositol group from phosphatidylinositol (PI) to phytoceramide, an essential step in sphingolipid biosynthesis (PubMed:19001565, PubMed:20309609). May play an important role in modulating plant programmed cell death (PCD) associated with defense (e.g. toward Golovinomyces cichoracearum) by promoting sphingolipid metabolism and thus regulating ceramide accumulation (PubMed:19001565). a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol) + an N-(2R-hydroxy-very-long-chain fatty acyl)-(R)-4-hydroxysphingoid base = a 1,2-diacyl-sn-glycerol + a 1D-myo-inositol-1-phospho-N-[(R)-2-hydroxy-very-long-chain fatty acyl]-(R)-4-hydroxysphingoid base Sphingolipid metabolism. Expressed in leaves, roots, stems, flowers and siliques. By powdery mildew (e.g. Golovinomyces cichoracearum and Pseudomonas syringae) inoculation. Constitutive RPW8-mediated HR-like cell death characterized by salicylic acid (SA) accumulation, enhanced transcription of RPW8 and RPW8-dependent spontaneous HR-like cell death (SHL) in leaf tissues. Reduced plant stature. Sphingolipid (e.g. ceramides and hydroxyceramides) accumulation associated with a reduced inositol-phosphorylceramide synthase (IPCS) activity. Belongs to the sphingomyelin synthase family.