Synthesis and Biological Evaluation of 1,2,4-Triazole Thioethers as Both Potential Virulence Factor Inhibitors against Plant Bacterial Diseases and Agricultural Antiviral Agents against Tobacco Mosaic Virus Infections

Targeting the virulence factors of phytopathogenic bacteria is an innovative strategy for alleviating or eliminating the pathogenicity and rapid outbreak of plant microbial diseases. Therefore, several types of 1,2,4-triazole thioethers bearing an amide linkage were prepared and screened to develop virulence factor inhibitors. Besides, the 1,2,4-triazole scaffold was exchanged by a versatile 1,3,4-oxadiazole core to expand molecular diversity. Bioassay results revealed that a 1,2,4-triazole thioether A 10 bearing a privileged N -(3-nitrophenyl)acetamide fragment was extremely bioactive against Xanthomonas oryzae pv. oryzae (Xoo) with an EC 50 value of 5.01 μg/mL. Label-free quantitative proteomics found that compound A 10 could significantly downregulate the expression of Xoo’s type III secretion system (T3SS) and transcription activator-like effector (TALE) correlative proteins. Meanwhile, qRT-PCR detection revealed that the corresponding gene transcription levels of these virulence factor-associated proteins were substantially inhibited after being triggered by compound A 10 . As a result, the hypersensitive response and pathogenicity were strongly depressed, indicating that a novel virulence factor inhibitor ( A 10 ) was probably discovered. In vivo anti-Xoo trials displayed that compound A 10 yielded practicable control efficiency (54.2–59.6%), which was superior to thiadiazole-copper and bismerthiazol (38.1–44.9%). Additionally, compound A 10 showed an appreciable antiviral activity toward tobacco mosaic virus (TMV) with the curative and protective activities of 54.6 and 76.4%, respectively, which were comparable to ningnanmycin (55.2 and 60.9%). This effect was further validated and visualized by the inoculation test using GFP-labeled TMV, thereby leading to the reduced biosynthesis of green-fluorescent TMV on Nicotiana benthamiana . Given the outstanding features of compound A 10, it should be deeply developed as a versatile agricultural chemical.