Plasmodesmata Localizing Proteins Regulate Transport and Signaling during Systemic Acquired Immunity in Plants

•SA and G3P/AzA are transported via the apoplast and symplast, respectively•Plasmodesmata localizing proteins PDLP1 and PDLP5 are required for SAR•Overexpression of PDLP5 impairs PD permeability and transport of G3P/AzA•PDLP1 interacts with, and contributes to, the intracellular partitioning of AZI1

SummarySystemic acquired resistance (SAR) in plants is mediated by the signaling molecules azelaic acid (AzA), glycerol-3-phosphate (G3P), and salicylic acid (SA). Here, we show that AzA and G3P transport occurs via the symplastic route, which is regulated by channels known as plasmodesmata (PD). In contrast, SA moves via the extracytosolic apoplast compartment. We found that PD localizing proteins (PDLP) 1 and 5 were required for SAR even though PD permeability in pdlp1 and 5 mutants was comparable to or higher than wild-type plants, respectively. Furthermore, PDLP function was required in the recipient cell, suggesting regulatory function in SAR. Interestingly, overexpression of PDLP5 drastically reduced PD permeability, yet also impaired SAR. PDLP1 interacted with AZI1 (lipid transfer-like protein required for AzA- and G3P-induced SAR) and contributed to its intracellular partitioning. Together, these results reveal the transport routes of SAR chemical signals and highlight the regulatory role of PD-localizing proteins in SAR.

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