A Non-Invasive Pathogen‑Responsive RUBY Reporter Enables Visible Monitoring of PR1 Activation.

We report a non‑invasive, pathogen‑responsive reporter system in Arabidopsis thaliana generated by placing the PR1 (AT2G14610) promoter upstream of the betalain‑producing RUBY cassette. Two independent transgenic lines showed robust, dose‑dependent red pigmentation accumulation in response to flg22 (a flagellin-derived peptide) and salicylic acid (a defense-signaling molecule that induces PR1 ) in both seedling and adult tissues. This reporter provides a simple, low‑cost visual readout of defense activation without the need for destructive sampling or specialized instrumentation. Seeds have been deposited at ABRC, and the plasmid has been made available through Addgene.