5-Fluoroindole Inhibits Its Putative Target Methionine Synthase and Pseudomonas syringae pv. actinidiae Virulence

Bacterial canker caused by Pseudomonas syringae pv. actinidiae (Psa) severely impacts global kiwifruit production. This study shows that 5-fluoroindole exerts significant bactericidal activity against Psa, with a half-maximal effective concentration (EC50) of 15.34 μg/mL, demonstrating a higher efficacy than the positive control copper hydroxide (EC50 = 58.65 μg/mL). 5-Fluoroindole disrupts membrane integrity, induces oxygen species (ROS) accumulation, and triggers apoptosis in Psa. Transcriptome analysis reveals that 5-fluoroindole treatment increased the expression of the methionine synthase II (MetE) gene by 6.28 fold compared with the expression of this gene in the control (CK) group. Microscale thermophoresis and isothermal titration calorimetry show that the dissociation constants of the binding of 5-fluoroindole to MetE protein are 0.33 and 8.55 μM, respectively. Molecular docking experiments indicate that Asp693 is a key binding site and that there is no specific binding between 5-fluoroindole and the Psa MetED693A mutant. This study provides valuable insights for developing effective agents to control kiwifruit bacterial canker.