Formononetin derivatives containing benzyl piperidine: A brand new, highly efficient inhibitor targeting Xanthomonas spp.

Introduction: Plant bacterial diseases take an incalculable toll on global food security. The indiscriminate use of chemical synthetic pesticide not only facilitates pathogen resistance of pathogenic bacteria, but also poses a major threat to human health and environmental protection. Therefore, it is of great economic value and scientific significance to develop a new antibacterial drug with environmental friendliness and unique mechanism of action.

Objectives: To design and synthesize formononetin derivatives based on natural products, evaluate their in vitro and in vivo antibacterial activities and elucidate the mechanisms involved.

Methods: The synthesis was carried out by classical active group splicing method. The antibacterial activities were evaluated using turbidimetry and pot experiments. The antibacterial mechanism was further investigated using scanning electron microscopy (SEM), virulence factors, defense enzymes activities, proteomics and metabolomics.

Results: 40 formononetin derivatives containing benzyl piperidine were designed and synthesized. The antibacterial results demonstrated that H32 exhibited the most potent inhibitory effect against Xanthomonas oryzae pv. Oryzae (Xoo) with the EC₅₀ of 0.07 μg/mL, while H6 displayed the highest inhibitory activity against Xanthomonas axonopodis pv. Citri (Xac) with the EC₅₀ of 0.24 μg/mL. Furthermore, the control efficacy of H32 against rice bacterial leaf blight (BLB) and H6 against citrus canker (CC) was validated through pot experiments. SEM, virulence factors and host enzyme activities assay indicated that H32 could not only reduce the virulence of Xoo, but also activate the activities of defense enzymes and improve the disease resistance of host plants. The proteomics and metabolomics analysis demonstrated that H32 could inhibit the synthesis of branched-chain amino acids, make Xoo cells in a starvation state, inhibit its proliferation, weaken its virulence and reduce its colonization and infection of host cells.

Conclusion: Formononetin derivatives containing benzyl piperidine could be used as potentially effective inhibitors against Xanthomonas spp.