Plasmodesmata localizing proteins regulate transport and signaling during systemic immunity. Arabidopsis thaliana cultivar:Columbia-0

Symplastic intracellular transport between adjacent cells occurs via channels known as plasmodesmata (PD). We show that phloem loading of the systemic acquired resistance (SAR)-inducing azelaic acid (AzA) and glycerol-3-phosphate (G3P) occurs via the symplast, whereas that of salicylic acid (SA) occurs via the apoplast. The PD localizing proteins (PDLP) 1 and 5, which regulate PD permeability, are involved in SAR; PD permeability is comparable to or ~25% higher than wild-type plants in the SAR defective pdlp1 and 5 mutants, respectively. Interestingly, constitutive or inducible overexpression of PDLP5, which drastically reduces (~70%) PD permeability, also impaires SAR. PDLP1 interacts with AZI1 (required for AzA- and G3P-induced SAR) and contributes to the intracellular partitioning of this lipid transfer-like protein. Together, these results reveal the transport routes of SAR chemical signals and highlight the regulatory role of PD localizing proteins in SAR.