FIGURE 2.

A schematic model describing the proposed functions for lipid transfer proteins (LTPs) in transporting lipid‐derived systemic acquired resistance (SAR) signals. During priming induction, MPK3/MPK6 promotes accumulation of AZI1 in plastids. AZI1/EARLI1 facilitates transport of SAR lipid signalling to the plasmodesmata (PD). Then, AZI1 interacts with plasmodesmata‐localizing protein 1 (PDLP1) and DIR1 in the plasmodesmata, transferring lipid signals to DIR1. The DIR1 and lipid signal complex is transferred to adjacent and systemic cells via the plasmodesmata. Lipid signalling then induces defence responses or transfer to AZI1 to further translocate SAR signals to other cells. Monoterpene (MT) induces a defence response via volatilized systemic tissues and neighbouring plants, where AZI1 mediates monoterpene‐induced defensive signal propagation. DIR1 is involved in dehydroabietinal (DA)‐induced SAR. AZI1 also might regulate systemic stomatal density (SD) via perception or transport of an unknown SAR signal (US).