Modulates cell-to-cell trafficking. Has a positive role in innate immunity. Required for systemic acquired resistance (SAR) which is mediated by the signaling molecules azelaic acid (AzA), glycerol-3-phosphate (G3P), and salicylic acid (SA) (PubMed:27078071). Negative regulator of plasmodesmata permeability triggered by SA during immune responses, through regulation of callose deposition (PubMed:21934146, PubMed:23749844). Delays the trafficking of Tobacco Mosaic Virus (TMV) movement protein (MP). Required for symplastic signal transport (PubMed:27078071). Monomer (PubMed:28876233). Interacts with PDLP1 (PubMed:27078071). (Microbial infection) Interacts with Grapevine fanleaf virus (GFLV) 2B-MP. Located in cell wall junctions between leaf epidermal and mesophyl cells. Located to the central region of plasmodesmata. Co-localizes with the Grapevine fanleaf virus (GFLV) 2B-MP at the base of tubules within modified plasmodesmata. Highly expressed in inflorescence nodes and rosette senescent leaves. Mostly expressed in cell wall junctions between leaf epidermal and mesophyl cells, and to a lesser extent at the cross walls between epidermal or cortex cells within the hypocotyl (at protein level). Low vascular expression in seedling and mature leaf, but high expression in senescing leaves (at protein level). By the Pseudomonas syringae pv. maculicola effector HopW1-1 (PubMed:18266921, PubMed:16531493). By salicylic acid (PubMed:21934146, PubMed:23749844). No growth defects (PubMed:21934146). Two-fold lower callose accumulation in plasmodesmata than wild type (PubMed:21934146). More susceptible to infection by the plant pathogen Pseudomonas syringae pv. maculicola (PubMed:21934146). Level of salicylic acid (SA) is comparable to wild type but plasmodesmata closure is impaired (PubMed:21934146, PubMed:23749844). However, overexpression leads to growth inhibition and chlorosis in seedling stage, with levels of SA fifteen-fold higher than wild type including all forms of SA, and probably triggering cell death (PubMed:23749844). Ectopic expression affects trafficking of MP from TMV, and shows four-fold accumulation of callose in plasmodesmata than wild type (PubMed:21934146). Compromised systemic acquired resistance (SAR) (PubMed:27078071). Belongs to the cysteine-rich repeat secretory protein family. Plasmodesmata-located proteins (PDLD) subfamily. PDLPs were initially named Cysteine-rich secretory proteins based on a classification work that failed to predict the transmembrane region at the C-terminus (PubMed:11402176). However, it was later shown that PDLPs are membrane proteins.