Jasmonate signalling drives rapid local and systemic immunity establishment

Systemic acquired resistance (SAR) provides plants with broad protection against many pathogens, but until recently, it was unclear how SAR signals are produced, transported, and expressed in distant tissues. In a new study in Nature Plants, Gaikwad and colleagues created a reporter construct that tracks these processes in real time. Following inoculation of leaves with Pseudomonas syringae expressing avrRpm1 to trigger effector-triggered immunity (ETI), JASMONATE-INDUCED SYSTEMIC SIGNAL 1 (JISS1), a protein in the endoplasmic reticulum with an unknown function, is activated quickly. Using a JISS1::LUC reporter, luciferase activity appeared in the petiole of locally treated leaves within 3 hours and spread to nearby leaves within 30 minutes, well before any visible cell death. Surprisingly, this fast signaling did not depend on the usual SAR components (SID2, NPR1, FMO1) or known SAR triggers. Instead, it relied on jasmonate production and sensing. Blocking JA-Ile synthesis with chemicals abolished or markedly attenuated DCavrRpm1-elicited JISS1::LUC activity in both local and systemic leaves, mirroring the phenotype observed in jasmonate biosynthesis (aos) and signaling (coi1-16) mutants. The researchers also found that ETI initiates jasmonate-dependent systemic surface electrical potentials that require both glutamate receptors and JISS1. However, neither glr mutants nor jiss1 loss-of-function lines lost SAR to Pseudomonas syringae, indicating that while these electrical potentials correlate with SAR signaling, they are not essential for establishing systemic resistance against this bacterial pathogen. Calcium signaling was also necessary, as the calcium inhibitor LaCl₃ completely inhibited reporter activity. This study challenges the idea that jasmonates undermine biotrophic immunity and instead shows that they are crucial for rapid SAR, offering new ways to study long-distance immune signaling. (Summary by Jahed Ahmed) Nature Plants 10.1038/s41477-025-02178-4