Plant bacterial diseases have caused substantial economic losses to agriculture worldwide and have seriously threatened the sustainable development of modern agriculture. Chemical control remains the most effective control method in the future. However, there are currently significant problems such as outdated varieties of agricultural antibacterial agents, low control efficacy, enhanced bacterial resistance, excessive pesticide residues, and a shortage of alternative varieties. To develop new, efficient and safe agricultural antibacterial agents, this article classifies antibacterial agrochemicals into oxadiazole/thiadiazole, triazole, isopropanolamine, onium salt, quinazoline, flavonoids, amide, ester, metal complex and others according to their active skeletons, and reviews the research on the SAR and action mechanisms of agricultural antibacterial agents in recent years. Summary the mechanisms of action of antibacterial agrochemicals was shown in
Fig. 11. Oxadiazole/thiadiazole compounds can not only enhance the activities of SOD, POD and chlorophyll in plants but also enhance various regulatory pathways, thereby enhancing resistance to bacteria. In addition, oxadiazole/thiadiazole compounds destroy the morphology of bacteria, enhance the permeability of cell membranes, and achieve the purpose of antibacterial. Exciting results have also been achieved in the discovery of targets. Song
et al. found through proteomics that compound
4 affects the motility and virulence of
Xoc. Subsequently, the ABPP technique was further employed to screen out the target proteins CsrA and Xoc3530. Moreover, using the ABPP technique, the target protein DLST of
Xoo and
Xac was also identified for compound
1. Triazole compounds also disrupt the morphology of bacteria and enhance the permeability of cell membranes. What is more, triazoles may downregulate the bacterial type Ⅲ secretion system and transcription activator-like effector related proteins, and interfere with bacterial redox system. However, the understanding of the mechanism of action of triazole compounds is mainly based on the phenotypic analysis of pathogenic bacteria and the detection of physiological and biochemical indicators. Their action targets and regulatory mechanisms remain unclear. Isopropanolamine compounds can achieve antibacterial effects through various pathways, such as disrupting cell morphology, influencing bacterial DNA, the redox system, the biosynthesis of DSF, biofilm formation, EPS synthesis, QS pathway proteins, T3SS, extracellular enzymes, fatty acid synthesis, and reducing the aggregation of bacterial flagella. In terms of target discovery, phenotypic experiments have suggested that the possible potential targets of compounds
26 and
28 are the RpfF protein in the QS pathway. Onium salts are electrostatically attracted to the negatively-charged bacterial cell membranes. Then, their hydrophobic chains interact with the negatively-charged phospholipids, thereby disrupting the bacterial morphology. Additionally, onium salts may also affect bacterial FtsZ and ribosomal proteins. In terms of target discovery, based on the approach of similar structures having similar mechanisms and the determination of GTPase activity, it was found that the target of compound
33 is FtsZ. The target was further verified through phenotypic observation, binding constant testing, circular dichroism, and Western blot. Quinazoline compounds may exert antibacterial effects through multiple pathways, including inhibiting fatty acid synthesis, affecting the synthesis and transport of ribosomal proteins, influencing proteins associated with bacterial flagellar biosynthesis, interfering with energy metabolism pathways, disrupting the T2SS and T4SS, suppressing the formation of EPS, altering membrane permeability, and destroying bacterial morphology. In terms of target discovery, the ABPP technique was used to identify that the target of compound
39 against
Xoo is FabF. The results of molecular docking show that compound
39 binds covalently to the Cys151 site in FabF. Flavonoid compounds disrupt the morphology of bacteria and enhance the CAT activity of the host. However, research on their mechanism of action is limited. It remains unknown whether these compounds can inhibit the energy metabolism, nucleic acid synthesis, and other pathways of plant bacteria. Moreover, the targets of flavonoids against plant bacterial diseases have not been discovered yet. Amide compounds have different antibacterial mechanisms. For example, compound
54 can reduce the HR of
Xoo without affecting bacterial growth, while compound
61 can disrupt the bacterial cell morphology, leading to the leakage of electrolytes and proteins, thus killing the bacteria. In terms of targets, Song
et al. used the ABPP technique to screen out that the target of compound
64 against
Xoo is pyruvate kinase, and verified the target through Western blot and enzyme activity assays. The Co-IP method, bacterial two-hybrid assay, and GST pull down assay were used to screen the interacting proteins of pyruvate kinase, which were identified as Clp and RegR. Similarly, Song
et al. used the ABPP technique to screen out that the target of compound
65 against
Xoo is Clp, and verified it through MST experiments, qRT-PCR, and experiments on constructing knockout mutants. Yang
et al. used the DARTS method to screen out that the target of compound
67 acting on
Xoo is the 50S ribosomal protein L2, which was confirmed by MST and fluorescence quenching spectroscopy. Moreover, compound
57, which was designed and synthesized based on FabH as the target, exhibits excellent antibacterial activity against
Xoo. Ester compounds may affect the expression of bacterial T3SS genes, thereby reducing virulence. Compounds
75 and
76 with excellent antibacterial activity were virtually screened based on the targets FtsZ and DHPS. Metal complexes not only interfere with a variety of bacterial virulence factors, affect signal transduction, involve metal sensing systems and metal uptake systems, but also protect plants from infection.