Abstract
The plant plasma membrane (PM) is an essential barrier between the cell and the external environment, controlling signal perception and transmission. It consists of an asymmetrical lipid bilayer made up of three different lipid classes: sphingolipids, sterols, and phospholipids. The glycosyl inositol phosphoryl ceramides (GIPCs), representing up to 40% of total sphingolipids, are assumed to be almost exclusively in the outer leaflet of the PM. However, their biological role and properties are poorly defined. In this study, we investigated the role of GIPCs in membrane organization. Because GIPCs are not commercially available, we developed a protocol to extract and isolate GIPC-enriched fractions from eudicots (cauliflower and tobacco) and monocots (leek and rice). Lipidomic analysis confirmed the presence of trihydroxylated long chain bases and 2-hydroxylated very long-chain fatty acids up to 26 carbon atoms. The glycan head groups of the GIPCs from monocots and dicots were analyzed by gas chromatograph–mass spectrometry, revealing different sugar moieties. Multiple biophysics tools, namely Langmuir monolayer, ζ-Potential, light scattering, neutron reflectivity, solid state 2H-NMR, and molecular modeling, were used to investigate the physical properties of the GIPCs, as well as their interaction with free and conjugated phytosterols. We showed that GIPCs increase the thickness and electronegativity of model membranes, interact differentially with the different phytosterols species, and regulate the gel-to-fluid phase transition during temperature variations. These results unveil the multiple roles played by GIPCs in the plant PM.
Highlights
The plant plasma membrane (PM) is an essential barrier between the cell and the external environment, controlling signal perception and transmission
The Glycosyl Inositol phosphatidyl ceramide (GIPC) head group linked to the ceramide consists of a phosphate bound to an inositol, forming the inositol phosphoryl ceramide (IPC) backbone, which is further substituted with further sugar moieties
We devised a new protocol to obtain milligram amounts of highly enriched GIPC samples from both monocots and eudicots, suitable for use in studies of GIPC structure and its role in PM organization. Using biophysics tools such as Langmuir monolayers, molecular modeling, supported lipid bilayers, giant unilamellar vesicles (GUVs), dynamic light scattering (DLS), ζ-potential, cryoelectron microscopy, solid state 2H-NMR, and neutron reflectivity, we aim to uncover the role of GIPCs, in synergy with sterols, in the plant PM organization
Summary
The plant plasma membrane (PM) is an essential barrier between the cell and the external environment, controlling signal perception and transmission. The glycosyl inositol phosphoryl ceramides (GIPCs), representing up to 40% of total sphingolipids, are assumed to be almost exclusively in the outer leaflet of the PM Their biological role and properties are poorly defined. We showed that GIPCs increase the thickness and electronegativity of model membranes, interact differentially with the different phytosterols species, and regulate the gel-to-fluid phase transition during temperature variations. Sphingolipids are part of essential lipids involved in the regulation of cellular signaling, trafficking, growth, and stress responses Ubiquitous to eukaryotes, they are structurally different between the animal, fungi, and plant kingdoms [3]. In Arabidopsis, the GIPC series A headgroup Man-GlcA-IPC is predominant in leaves and callus [15, 16], whereas a complex array of N-acetyl glycosylated with up to three pentose units are present in pollen [17]. The predominant GIPC series is series B [7], their core structures are yet to be deciphered
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