Fig. 7.

Integrated hypothetical model representing the different proteins enriched in the poplar DRM and the biological processes in which they are involved. Proteins whose names are highlighted in blue were shown to be enriched in plasma membrane DRMs (gray patches) together with other proteins listed in Table I. All proteins enriched in DRMs are markers of signal transduction, molecular transport, and callose biosynthesis and are known to be involved in biotic and/or abiotic stress. Vesicles carrying proteins involved in endocytosis and exocytosis and cell wall biosynthetic enzymes (callose synthases or GSL) are represented by green circles. The represented cascade of events leads to the release of calcium on the cytoplasmic side of the plasma membrane, which is required for the activation of callose synthase as a final response to stress (80). The enrichment of callose synthase in DRMs suggests a preferential deposition of callose plugs at the surface of plasma membrane microdomains, possibly in specialized plasmodesmatal structures and/or other sites of the plasma membrane. DAG, diacylglycerol; DGK, diacylglycerol kinase; ER, endoplasmic reticulum; GSL, glucan synthase-like/callose synthase; IP3, inositol-3-phosphate; PIP, phosphatidyl-inositol-phosphate; PL, phospholipid; PLC, phosphatidyl-inositol phospholipase C; PLD, phospholipase D; PM, plasma membrane; SCAMP, secretory carrier membrane protein; SNAP, soluble NSF attachment protein; SNARE, SNAP receptor.