P-263 - Suppression of defense gene expression under nutrient-rich condition in Arabidopsis seedlings

Chemicals called plant activators (PAs) including probenazole, acibenzolar-s-methyl and 2,6-dichloroisonicotinic acid activate plant immune systems, providing protection against pathogens. Unlike conventional pesticides that directly target pathogens, PAs boost the host's defense mechanisms, potentially reducing the likelihood of drug resistance development. Various high-throughput screening systems（HTS）have been developed with the aim of searching for PAs. Transgenic Arabidopsis lines harboring defense gene promoter-luciferase reporter fusion gene allow us to monitor the activity of defense-related gene in vivo. To investigate the influence of nutrients on the HTS system, we conducted luciferase assays using Arabidopsis seedlings and observed the suppression of defense gene expression in response to the treatment of PAs. Reverse transcription quantitative polymerase chain reaction was employed to monitor the expression levels of endogenous genes in response to nutrient-rich conditions and confirmed the suppression effect of defense gene expression as observed in the luciferase reporter assays. The results highlight the importance of considering nutrient effects when evaluating PAs and screening for compounds that induce defense gene expression under nutrient-rich conditions. Based on these findings, using luciferase-reporter based HTS, we have identified novel PA candidates that induce defense gene expression even under eutrophic conditions.