Agrivax: A chemical inducer of plant immunity identified by high-throughput screening.

Plants possess a multilayered immune system that detects and responds to pathogen invasion through pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). We recently developed a high-throughput screening platform using transgenic Arabidopsis thaliana expressing the β-glucuronidase (GUS) reporter gene under the control of the promoter of the PTI marker gene FRK1 (pFRK1::GUS) to identify chemical inducers of plant immunity. Among the ∼10,000 screened compounds, we identified 10 candidate compounds with the potential to activate FRK1 expression. In this study, we focused on one of these small molecules, designated Agrivax, for analysis. Agrivax is a previously unreported small molecule that activates immune signaling. Agrivax induces FRK1 expression in a dose-dependent manner, triggers the transient phosphorylation of MAPKs, and enhances resistance against Pseudomonas syringae pv. tomato DC3000 (Pst DC3000). While Agrivax alone did not elicit reactive oxygen species (ROS) production, it synergistically amplified flg22-and chitin-induced ROS bursts and root growth inhibition. Furthermore, Agrivax pretreatment potentiated the ETI-associated hypersensitive response upon challenge with Pst DC3000 carrying AvrRpt2. These findings demonstrate that Agrivax functions as an immune priming chemical to activate immune responses and disease resistance, making it a promising lead compound for developing plant immune inducers and a valuable tool for dissecting immune signaling pathways.