Plant VAP27 proteins: domain characterization, intracellular localization, and role in plant development.

• The endoplasmic reticulum (ER) is connected to the plasma membrane (PM) through the plant specific NETWORKED protein, NET3C, and phylogenetically conserved Vesicle-Associated Membrane Protein-Associated Proteins (VAPs). • Ten VAP homologues (VAP27-1 to 10) can be identified in the Arabidopsis genome and can be divided into three clades. Representative members from each clade have been tagged with fluorescent protein and expressed in Nicotiana benthamiana. • Proteins from clades one and three localised to the ER as well as to ER/PM contact sites (EPCS), whereas proteins from clade two are found only at the PM. Some of the VAP27 labelled EPCS localised to plasmodesmata, and we show that the mobility of VAP27 at the EPCS is influenced by the cell wall. EPCS closely associate with the cytoskeleton, but their structure is unaffected when the cytoskeleton is removed. • VAP27 labelled EPCS are found in most cell types in Arabidopsis with the exception of cells in early trichome development. Arabidopsis expressing VAP27-GFP fusions exhibit pleiotropic phenotypes including defects in root hair morphogenesis. A similar effect is also observed in plants expressing VAP27 RNAi. • Taken together these data indicate that VAP27 proteins used at the EPCS are essential for normal ER-cytoskeleton interaction and for plant development