WRKY Group I Transcription Factor Regulates a Strictosidine Synthase-Like Gene and Acts as a Negative Regulator in Bacillus cereus AR156-Induced Systemic Resistance Against Tomato Bacterial Wilt

Induced systemic resistance (ISR) is an essential strategy in biological control. Previous research has shown that Bacillus cereus AR156 can trigger ISR to defend against multiple pathogens, though the underlying mechanisms may vary depending on the pathogen. However, the specific mechanism by which AR156 induces systemic resistance against Ralstonia solanacearum in tomatoes remains unclear. In this study, we focused on WRKY group I transcription factors and identified WRKY4, which is downregulated by AR156 induction. Further analysis confirmed that WRKY4 functions as a negative regulator in AR156-ISR against tomato bacterial wilt. Experimental results demonstrated that WRKY4 is localized in the nucleus and exhibits transcriptional regulatory activity. Subsequent screening revealed that WRKY4 directly targets the promoter region of the SSL3 (Strictosidine Synthase-Like) gene, which encodes a key synthase for metabolic precursors, and consequently suppresses its expression. Finally, we confirmed that WRKY4 negatively regulates SSL3 expression, contributing to AR156-ISR against tomato bacterial wilt as a key negative regulator. Our research enriches our understanding of the ISR network and provides a theoretical foundation for the biological control of diseases. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2026.