Mechanism of action of isobavachalcone in inducing resistance to tobacco mosaic virus disease in tobacco

Isobavachalcone (IBC), a natural active compound derived from the seeds of Psoralea corylifolia L., is a botanical fungicide that has been shown to effectively manage various plant diseases caused by pathogenic fungi, bacteria, and viruses in agricultural settings. However, the mechanism by which IBC induces tobacco resistance to tobacco mosaic virus (TMV) infection remains unclear. In this study, tobacco plants at the 6～8 leaf stage were treated with 40 mg/L IBC three times before inoculation with TMV. At 24 h post-inoculation, differentially expressed genes between the IBC-treated group and the inoculated control group were mainly enriched in plant hormone signal transduction and MAPK(mitogen-activated protein kinase)signaling pathways. The expression levels of positive regulatory factors JAR1, SnRK2, ABF, FLS2, and PR in the above signaling pathways were significantly up-regulated, while the expression level of the negative regulatory factor JAZ was significantly down-regulated. From 1 to 9 days post-inoculation, the activities of four defense enzymes, SOD, PPO, PAL, and POD, in the IBC-treated tobacco leaves were significantly higher than those in the inoculated control. These results suggest that IBC activates the MAPK signaling pathway in plants, regulates the coordination of SA, JA, and ABA plant hormone signaling networks in immune responses, and increases the activities of pathogenesis-related proteins and defense enzymes in tobacco to induce resistance against TMV. This study reveals the mechanism of IBC-induced resistance against TMV in tobacco at the transcriptomic and physiological-biochemical levels, providing a theoretical basis for the widespread application of IBC in agriculture.