Design and research of new virulence factor inhibitors for plant bacterial disease control

Abstract

• Compound Z6 showed notable biological activity, with a median effective concentration (EC 50 ) of 0.29 mg/L against Xanthomonas oryzae pv. oryzae ( Xoo ) in vitro , which was higher than thiodiazole copper (TC, 91.00 mg/L). Similarly, Z21 exhibited a strong biological response (EC 50 = 0.83 mg/L) against Xanthomonas axonopodis pv. citri ( Xac ), outperforming TC (EC 50 = 114.60 mg/L). • Following the result of EC 50 values, Z6 (0.29 mg/L) and Z16 (0.32 mg/L) were mixed in a specific ratio ( v/v ) by the method of combination and synergism. The results showed that as the proportion of Z6 increases, the inhibition rate also increases. Consequently, Z6 was chosen as the focus for subsequent in vivo activity testing and mechanism research. • Results of bioactivity test in vivo demonstrate that Z6 displayed significantly better curative and protective activities (51.5%, 47.9%) than TC (47.9%, 30.5%) against rice bacterial leaf blight (BLB). • Mechanistic studies revealed that Z6 can regulate the expression of various VFs, including extracellular polysaccharides, extracellular enzymes, and biofilms, leading to the inhibition of Xoo. Subsequent measurements of chlorophyll content, POD, SOD and CAT activities in rice leaves indicated that Z6 enhances plant photosynthetic ability, increases antioxidant enzymes activities and mitigates the formation of hydroxyl radicals, thereby safeguarding the membrane system from harm. In this work, various chalcone derivatives incorporating piperazine-isopropanolamine were elaborately designed and synthesized. The antibacterial efficacy revealed that compound Z6 showed notable biological activity, with a median effective concentration (EC 50 ) of 0.29 mg/L against Xanthomonas oryzae pv. oryzae ( Xoo ) in vitro , which is around 200 times higher than thiodiazole copper (TC, 91.00 mg/L). Similarly, Z21 exhibited a strong biological response (EC 50 = 0.83 mg/L) against Xanthomonas axonopodis pv. citri ( Xac ), outperforming TC (EC 50 = 114.60 mg/L). Results of bioactivity test in vivo demonstrate that Z6 displayed significantly better curative and protective activities (51.5 %, 47.9 %) than TC (47.9 %, 30.5 %) against rice bacterial leaf blight (BLB). Further biochemical studies indicates that Z6 targeted multiple virulence factors and repressed the release of essential nutrients required for bacterial proliferation, thereby disrupting the reduction of cell membrane content of the pathogenic bacteria. According to the research, chalcone derivatives containing piperazine-isopropanolamine have potential to be antibacterial candidates.