Abstract text: In plants, the plasma membrane controls signal perception and transmission, with glycosylinositolphosphorylceramides (GIPCs) as its major outer-leaflet sphingolipids bearing complex glycosylated polar heads. They consist of a membrane-anchored lipid moiety and large glycosylated polar heads facing the cell wall. In plants, GIPCs contain glucuronic acid linked to IPC, followed by mannose or glucosamine, with additional sugars forming complex series of up to ten residues, composition largely unknown.

A HPSEC–HRMS/MS approach developed in the GAS team (IJPB-INRAE) is designed to address two complementary objectives. First, it elucidates poorly characterized GIPC polar head structures using an enzymatic fingerprinting strategy that selectively cleaves them, releasing inositol phosphoglycans (IPGs) from the lipid moiety and enhancing their mass spectrometric detection.

We next analyzed plant mutants impaired in GIPC glycosylation or in activated sugar biosynthesis/transport and uncovered an unexpected structural complexity of GIPCs, including atypical sugars, prompting a reassessment of phenotypes previously attributed solely to cell wall defects.

Finally, we showed that, like plant cell wall polysaccharides, all GIPC series are continuously remodeled by GIPC-specific phospholipases in planta, generating inositol phosphate–containing oligosaccharides with potential signaling roles. We demonstrated that these oligosaccharides were biologically active in planta, protecting plants against a major phytopathogen by activating signaling pathways.