Signals in systemic acquired resistance of plants against microbial pathogens

After a local infection by the microbial pathogens, plants will produce strong resistance in distal tissues to cope with the subsequent biotic attacks. This type of the resistance in the whole plant is termed as systemic acquired resistance (SAR). The priming of SAR can confer the robust defense responses and the broad-spectrum disease resistances in plants. In general, SAR is activated by the signal substances generated at the local sites of infection, and these small signaling molecules can be rapidly transported to the systemic tissues through the phloem. In the last two decades, numerous endogenous metabolites were proved to be the potential elicitors of SAR, including methyl salicylate (MeSA), azelaic acid (AzA), glycerol-3-phosphate (G3P), free radicals (NO and ROS), pipecolic acid (Pip), N-hydroxy-pipecolic acid (NHP), dehydroabietinal (DA), monoterpenes (alpha-pinene and beta-pinene) and NAD(P). In the meantime, the proteins associated with the transport of these signaling molecules were also identified, such as DIR1 (DEFECTIVE IN INDUCED RESISTANCE 1) and AZI1 (AZELAIC ACID INDUCED 1). This review summarizes the recent findings related to synthesis, transport and interaction of the different signal substances in SAR.

Automated summary

After local infection by microbial pathogens, plants develop systemic acquired resistance (SAR) to defend against subsequent biotic attacks. SAR, activated by signal substances at local infection sites, can provide robust defense responses in plants. The signaling molecules, including endogenous metabolites and associated proteins, play crucial roles in the synthesis, transport, and interaction of SAR.