Trends in Plant Science
ReviewMembrane rafts in plant cells
Section snippets
Plasma membrane heterogeneity: the membrane raft concept
Biological membranes, particularly the plasma membrane (PM), are no longer considered as bilayers composed of homogenously distributed lipids and proteins. Instead, research carried out by biologists, biophysicists, and biochemists has revealed over the past 15 years the existence within the PM of particular domains (rafts) that exhibit a specific molecular composition. These domains are enriched in sterol and sphingolipids, and depleted in unsaturated phospholipids. Self-associating properties
Detergent insolubility of plant membranes: facts and artefacts
The highly compact structure of the Lo phase prevents the incorporation of detergent molecules, thus making membrane rafts more resistant to non-ionic detergent treatment than the fluid non-raft membrane surrounding them. A marked correlation can be observed between the detergent solubilisation of a cell membrane monitored by confocal microscopy of raft marker proteins and that of supported lipid bilayers imaged by atomic force microscopy [8]. Because of this property, the studies of membrane
Insights into membrane domain organization
It is clear from studies on animal cells that the principles of lipid self-association of sterols and sphingolipids can confer organization beyond non-specific fluidity [33]. The extraction of free sterols from isolated tobacco PM using MCD increases lipid acyl chain disorder and reduces the overall liquid-phase heterogeneity, which correlates with the disruption of phytosterol-rich domains [34]. Furthermore, MCD treatment also prevents isolation of DIMs. These results point to a role of
From DIMs to membrane rafts
Besides isolating DIMs and demonstrating with model membranes that particular species of lipids are able to form distinct phases within the membrane, a crucial objective for researchers has been to develop a way of visualizing membrane rafts in situ and to characterize the lateral heterogeneity of the plant PM.
Modelling studies are consistent with the idea that rafts are 10–100 nm in diameter 36, 37, progressively shifting from a microdomain to a nanodomain model. This estimated size, far below
Membrane rafts in plant physiology
There is strong evidence for the involvement of sterol-enriched membrane domains in plant physiology. Because of space constraints, we will only focus on cell polarity and signal transduction in this review. For reviews of aspects of cell trafficking and raft formation along the secretory pathway, see 23, 56. The first set of data concerns growth and development. The polarized transport of the plant hormone auxin depends on AUX1/LAX, PGP and PIN protein families that mediate auxin transport
Conclusions and future perspectives
The existence of a lateral heterogeneity of the distribution of lipids and proteins on the plant PM has been established the last few years. The role of sterols in the maintenance of part of this heterogeneity and its variations in response to environmental constraints has also been evidenced. However, much research remains to be done to understand in more detail what covers this heterogeneity (i.e. are there different types of domains; how many domains; how to characterize them according to
Acknowledgements
We thank Andy Maule, Christophe Ritzenthaler and Vivienne Gianinazzi-Pearson for critical reading of the manuscript, and Elodie Noirot and Alain Glowczack for help with figure design. We acknowledge the French ‘Agence Nationale pour la Recherche’ (ANR) for financial support (contracts NT09_517917 PANACEA to S.M. and F.S-P). We apologize to all those colleagues whose work was not cited because of space restriction.
The authors declare that they have no conflict of interest.
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