Mobile signals in systemic acquired resistance

Plants possess a unique form of broad-spectrum long-distance immunity termed systemic acquired resistance (SAR). SAR involves the rapid generation of mobile signal(s) in response to localized microbial infection, which transport to the distal tissue and 'prime' them against future infections by related and unrelated pathogens. Several SAR-inducing chemicals that could be classified as the potential mobile signal have been identified. Many of these function in a bifurcate pathway with both branches being equally essential for SAR induction. This review reflects on the potential candidacy of the known SAR inducers as mobile signal(s) based on historical knowledge of the SAR signal and recent advances in the SAR signaling pathway.