The endoplasmic reticulum (ER) is a ubiquitous organelle that plays roles in secretory protein production, folding, quality control, and lipid biosynthesis. The cortical ER in plants is pleomorphic and structured as a tubular network capable of morphing into flat cisternae, mainly at three-way junctions, and back to tubules. Plant reticulon family proteins (RTNLB) tubulate the ER by dimerization and oligomerization, creating localized ER membrane tensions that result in membrane curvature. Some RTNLB ER-shaping proteins are present in the plasmodesmata (PD) proteome and may contribute to the formation of the desmotubule, the axial ER-derived structure that traverses primary PD. Here, we investigate the binding partners of two PD-resident reticulon proteins, RTNLB3 and RTNLB6, that are located in primary PD at cytokinesis in tobacco (Nicotiana tabacum). Coimmunoprecipitation of green fluorescent protein-tagged RTNLB3 and RTNLB6 followed by mass spectrometry detected a high percentage of known PD-localized proteins as well as plasma membrane proteins with putative membrane-anchoring roles. Förster resonance energy transfer by fluorescence lifetime imaging microscopy assays revealed a highly significant interaction of the detected PD proteins with the bait RTNLB proteins. Our data suggest that RTNLB proteins, in addition to a role in ER modeling, may play important roles in linking the cortical ER to the plasma membrane.The endoplasmic reticulum (ER) is a multifunctional organelle and is the site of secretory protein production, folding, and quality control (Brandizzi et al., 2003) and lipid biosynthesis (Wallis and Browse, 2010), but it is also involved in many other aspects of day-to-day plant life, including auxin regulation (Friml and Jones, 2010) and oil and protein body formation (Huang, 1996;Herman, 2008). The cortical ER network displays a remarkable polygonal arrangement of motile tubules that are capable of morphing into small cisternae, mainly at the three-way junctions of the ER network (Sparkes et al., 2009). The cortical ER network of plants has been shown to play multiple roles in protein trafficking (Palade, 1975;Vitale and Denecke, 1999) and pathogen responses (for review, see Pattison and Amtmann, 2009;Beck et al., 2012).In plants, the protein family of reticulons (RTNLBs) contributes significantly to tubulation of the ER (Tolley et al., 2008Chen et al., 2012). RTNLBs are integral ER membrane proteins that feature a C-terminal reticulon homology domain (RHD) that contains two major hydrophobic regions. These regions form two V-shaped transmembrane wedges joined together via a cytosolic loop, with the C and N termini of the protein facing the cytosol. RTNLBs can dimerize or oligomerize, creating localized tensions in the ER membrane, inducing varying degrees of membrane curvature . Hence, RTNLBs are considered to be essential in maintaining the tubular ER network.The ability of RTNLBs to constrict membranes is of interest in the context of cell plate development and the formation of primary plasmo...