Remorins (REMs) are proteins of unknown function specific to vascular plants. We have used imaging and biochemical approaches and in situ labeling to demonstrate that REM clusters at plasmodesmata and in ∼70-nm membrane domains, similar to lipid rafts, in the cytosolic leaflet of the plasma membrane. From a manipulation of REM levels in transgenic tomato (Solanum lycopersicum) plants, we show that Potato virus X (PVX) movement is inversely related to REM accumulation. We show that REM can interact physically with the movement protein TRIPLE GENE BLOCK PROTEIN1 from PVX. Based on the localization of REM and its impact on virus macromolecular trafficking, we discuss the potential for lipid rafts to act as functional components in plasmodesmata and the plasma membrane.

Lipid composition of plasma membrane (PM) and the corresponding Detergent-Insoluble Membrane (DIM) fraction were analyzed with a specific focus on highly polar sphingolipids so-called Glycosyl-Inositol-Phosphoryl-Ceramides (GIPCs). Using tobacco Bright Yellow-2 cell suspension and tobacco leaves (Nicotiana tabacum), evidences were provided that GIPCs represent up to 40 mol% of the PM lipids. Comparative analysis of DIMs with the PM showed an enrichment of 2-hydroxylated Very Long Chain Fatty Acid (VLCFA)-containing GIPCs and polyglycosylated GIPCs in the DIMs. Purified antibodies raised against these GIPCs were further used for immunogold-electron microscopy strategy, revealing the distribution of polyglycosylated GIPCs in domains of 35{plus minus}7nm in the plane of the PM. Biophysical studies also showed strong interactions between GIPCs and sterols, and suggested a role for VLCFA in the interdigitation between the two PM composing-monolayers. The ins and outs of lipid asymmetry, raft formation and interdigitation in plant membrane biology are finally discussed.

In grape (Vitis vinifera), abscisic acid (ABA) accumulates during fruit ripening and is thought to play a pivotal role in this process, but the molecular basis of this control is poorly understood. This work characterizes ABSCISIC ACID RESPONSE ELEMENT-BINDING FACTOR2 (VvABF2), a grape basic leucine zipper transcription factor belonging to a phylogenetic subgroup previously shown to be involved in ABA and abiotic stress signaling in other plant species. VvABF2 transcripts mainly accumulated in the berry, from the onset of ripening to the harvesting stage, and were up-regulated by ABA. Microarray analysis of transgenic grape cells overexpressing VvABF2 showed that this transcription factor up-regulates and/or modifies existing networks related to ABA responses. In addition, grape cells overexpressing VvABF2 exhibited enhanced responses to ABA treatment compared with control cells. Among the VvABF2-mediated responses highlighted in this study, the synthesis of phenolic compounds and cell wall softening were the most strongly affected. VvABF2 overexpression strongly increased the accumulation of stilbenes that play a role in plant defense and human health (resveratrol and piceid). In addition, the firmness of fruits from tomato (Solanum lycopersicum) plants overexpressing VvABF2 was strongly reduced. These data indicate that VvABF2 is an important transcriptional regulator of ABA-dependent grape berry ripening.

Elicitors are molecules known to trigger plant defence responses against pathogens. In a search for new sources of eliciting compounds from marine algae, an extract was prepared from green algae, Ulva spp., and its elicitor activity was established on the model legume, Medicago truncatula. When infiltrated into plant tissues or sprayed onto the leaves, this extract induced the expression of the defence‐related marker gene PR10 without provoking necrosis. Spraying a solution at 500 µg mL⁻¹ was sufficient to obtain maximum induction of PR10 after 2 d. Using a cDNA array enriched in genes potentially involved in plant defence, the expression of 152 genes was monitored after one or two consecutive treatments. A broad range of defence‐related transcripts was found to be up‐regulated, notably genes involved in the biosynthesis of phytoalexins, pathogenesis‐related proteins and cell wall proteins. In contrast, the expression of primary metabolism‐related genes did not change significantly. Consistent with its effect on defence gene expression, it was found that prior treatment of M. truncatula with the Ulva extract protected the plants against subsequent infection by the pathogenic fungus Colletotrichum trifolii.