Phenolic Compound 3-Methylcinnamic Acid Produced by Bacillus cereus BR3 Suppresses the Pathogenicity of Xanthomonas campestris pv campestris

Cabbage black rot, caused by Xanthomonas campestris pv campestris (Xcc), is a severe disease worldwide. The predominant method for controlling this disease relies on agrichemicals, which increase antibiotic resistance. This study showed that the secondary metabolites of B. cereus BR3 elicited induced systemic resistance in cabbage and impaired the type III secretion system (T3SS) of Xcc. Furthermore, the extract of strain BR3 significantly enhanced the activities of plant-defense-related enzymes, suppressed the hypersensitive response (HR) induced by Xcc in tobacco, and attenuated the pathogenicity of Xcc on cabbage. Additionally, several genes of Xcc T3SS were repressed by the BR3 extract. Activity-guided purification identified 3-methylcinnamic acid as an effective inhibitor against the T3SS of Xcc. Overall, this study suggests that 3-methylcinnamic acid produced by strain BR3 disrupts a critical virulence mechanism in Xcc, providing a promising alternative for controlling the black rot disease in cabbage.