Discovery of novel plant immune-priming compounds through WRKY45 promoter-based chemical screening

Plant activators enhance disease resistance by priming host immunity, offering a sustainable alternative or complement to conventional pesticides. To advance this field, we established a high-throughput screening platform based on activation of the rice WRKY45 promoter, a central regulator of disease resistance. From a library of 80,232 compounds, we identified five novel plant immune-priming compounds (PIPC1–5) that significantly enhanced resistance to rice blast caused by Magnaporthe oryzae following seed or foliar application. These PIPCs showed no direct antifungal activity, indicating that they act through activation of host defense responses. The PIPCs also conferred broad-spectrum resistance to rice bacterial blight (Xanthomonas oryzae pv. oryzae), rice false smut (Ustilaginoidea virens), pepper spotted wilt (tomato spotted wilt virus), and downy mildew of Chinese cabbage (Hyaloperonospora brassicae). Notably, PIPCs lack the thiazole ring characteristic of classical salicylic acid (SA) pathway activators such as probenazole and benzothiadiazole, representing a novel chemical scaffold. Mechanistically, the PIPCs primed rice seedlings to establish immune memory by acting either upstream or downstream of SA synthesis, thereby accelerating defense gene induction upon subsequent pathogen challenge. These findings expand the repertoire of immune-priming agents for managing diverse and evolving crop pathogens.