Specific Membrane Lipid Composition Is Important for Plasmodesmata Function in Arabidopsis

Abstract

Plasmodesmata (PD) are nano-sized membrane-lined channels controlling intercellular communication in plants. Although progress has been made in identifying PD proteins, the role played by major membrane constituents, such as the lipids, in defining specialized membrane domains in PD remains unknown. Through a rigorous isolation of "native" PD membrane fractions and comparative mass spectrometry-based analysis, we demonstrate that lipids are laterally segregated along the plasma membrane (PM) at the PD cell-to-cell junction in Arabidopsis thaliana. Remarkably, our results show that PD membranes display enrichment in sterols and sphingolipids with very long chain saturated fatty acids when compared with the bulk of the PM. Intriguingly, this lipid profile is reminiscent of detergent-insoluble membrane microdomains, although our approach is valuably detergent-free. Modulation of the overall sterol composition of young dividing cells reversibly impaired the PD localization of the glycosylphosphatidylinositolanchored proteins Plasmodesmata Callose Binding 1 and the b-1,3-glucanase PdBG2 and altered callose-mediated PD permeability. Altogether, this study not only provides a comprehensive analysis of the lipid constituents of PD but also identifies a role for sterols in modulating cell-to-cell connectivity, possibly by establishing and maintaining the positional specificity of callosemodifying glycosylphosphatidylinositol proteins at PD. Our work emphasizes the importance of lipids in defining PD membranes.

Glycosylphosphatidylinositol (GPI) modification serves as a primary plasmodesmal targeting signal

“…It was found recently that the region of the PM that lines the Pd channel is highly enriched in sphingolipids and sterols (Grison et al, 2015). Moreover, it was shown that Pd localization of GPI-APs, like PDCB1 and PDBG2, could be disrupted by inhibiting the sterol biosynthesis pathway (Grison et al, 2015).…”

“…It was found recently that the region of the PM that lines the Pd channel is highly enriched in sphingolipids and sterols (Grison et al, 2015). Moreover, it was shown that Pd localization of GPI-APs, like PDCB1 and PDBG2, could be disrupted by inhibiting the sterol biosynthesis pathway (Grison et al, 2015). In addition, proteomic analysis of sterol-enriched detergent-resistant membranes in Arabidopsis revealed that GPI-APs are overrepresented in those membranes (Kierszniowska et al, 2009).…”

“…Recently, Grison et al (2015) showed that mCherry-tagged PDCB1 without the GPI signal, but with its C-terminal unstructured region, had a soluble apoplastic localization pattern with no Pd enrichment, suggesting that the unstructured region in PDCB1 might have a role in enhancing the export of CBM43 CB from the ER. Similar effects were shown with other plant GPI-APs, in which deletion of the GPI signal resulted either in a complete lack of protein export (Lee et al, 2009;Li et al, 2015;Deng et al, 2016) or soluble extracellular accumulation with no PM fraction (Sun et al, 2004;Li et al, 2010).…”

“…Recent studies have shown that the region of the plasma membrane (PM) lining the Pd channel is a specialized membrane microdomain whose lipid and protein composition differs from the rest of the PM (Tilsner et al, 2011(Tilsner et al, , 2016Bayer et al, 2014;González-Solís et al, 2014;Grison et al, 2015). In a similar manner, the cell wall domain surrounding the Pd channel is specialized and, unlike the rest of the cell wall, is devoid of cellulose, rich in pectin, and contains callose (an insoluble b-1,3-glucan; Zavaliev et al, 2011;Knox and BenitezAlfonso, 2014).…”

Sterols Modulate Cell-to-Cell Connectivity at Plasmodesmata

“…Lipids are also thought to affect the structure and function of PD (Delage and Zurzolo, 2013), but little is known about the lipid constituents of PD. Grison et al (2015) analyzed the lipid composition of membranes lining primary PD using highly purified PD-derived membranes from Arabidopsis thaliana suspension cells. A comparative mass spectrometry-based analysis showed that the lipid composition of PD membranes differed from that of the surrounding plasma membrane, with PD membranes being enriched in sterols and complex sphingolipids with very long saturated fatty acid tails.…”