Mapping the propagation of a salicylic acid wave during pathogen spread using a fluorescent sensor

Salicylic acid (SA) is a central signaling molecule in systemic acquired resistance (SAR) in plants, yet long-term monitoring of its real-time dynamics in living tissues has remained technically challenging. Using the recently developed genetically encoded fluorescent sensor SalicS1, high-resolution spatiotemporal imaging of SA was successfully performed in intact plants for the first time, revealing an SA wave that propagates ahead of the invading pathogen. This breakthrough tool directly captures the dynamic spread of plant defense signals. In addition, SalicS1 provides a technological foundation for dissecting the temporal relationships between SA and upstream early signals such as calcium ions and reactive oxygen species and for identifying novel immune signaling components through genetic screening. The development of this sensor marks a transition in plant immunity research from static measurements to real-time dynamic imaging.