E. Bayer - Lateral segregation of plasma membrane lipids across plasmodesmata cell boundary: a role for lipids in the regulation of intercellular trafficking?

Abstract:

To compartmentalize and coordinate biological processes, membrane bilayers have evolved the propensity to segregate their constituents laterally thereby acquiring the ability to organise domains with specialised functions. Plasmodesmata (PD) are compelling examples of such membrane functional sub-compartmentalisation with the specialisation of the endoplasmic reticulum (ER) and the plasma membrane (PD-PM) across cell boundary. Functionality at PD hinges on the molecular specification of both membrane domains.

Although progress has been made in defining PD protein constituents, the role played by major membrane constituents, e.g. the lipids, in defining PD membrane domains remains completely uncovered. Not only the lipid composition of PD membranes is currently unknown but the contribution of membrane lipids in the regulation of intercellular communication in plant remains unexplored. Yet research in biological membrane over the last decade has unequivocally demonstrated that lipids are functional units that can modulate membrane organisation and cellular function.

In this work we have focussed our attention on the specialised PD-PM domain with the aim to characterise its lipid composition. Through the rigorous isolation of “native” PD membrane fractions and comparative mass spectrometry-based analysis, we demonstrate that not only proteins but also lipids are laterally segregated along the PM at site of cell-to-cell junctions. Remarkably, our results showed that the PD membrane domain displayed a significant enrichment in complex sphingolipids, sterols and glycerolipids containing saturated fatty acids when compared to the bulk of the PM. Modulating the overall sterol composition of young dividing cells reversibly impaired targeting of GPI-anchored proteins to the PD channels. Altogether, this study not only provides for the first time a comprehensive analysis of the lipid constituents of PD but also identifies a role for sterols in establishing and maintaining positional specificity at PD. Our work emphasizes the importance of the lipid composition in defining PD membrane domains.

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