Mikanolide enhances tobacco TMV resistance by strengthening cell walls via EXP/PG repression and activating defense via LYKs.

Tobacco mosaic virus (TMV) is a major pathogen of Solanaceae, threatening tobacco yield and quality. In this study, 12 compounds from Mikania micrantha were evaluated for their inhibitory effects on TMV using the half-leaf method and ID-ELISA assay. Compound 1 (Mikanolide) showed superior protective (63.43 %) and therapeutic (69.09 %) activities compared to other compounds and Ningnanmycin. It also exhibited inactivation (50.98 %) and proliferation inhibition (60.64 %) against TMV. Molecular docking revealed its binding to TMV-CP through hydrogen and hydrophobic bonds. Mechanistic analyses indicated that Mikanolide elevated chlorophyll contents, flavonoid and total phenol biosynthesis, and salicylic acid accumulation, thereby enhancing defense-related enzymatic activity. Transcriptome analyses showed increased expression of cell wall-related EXP and PG genes, as well as LYKs defense response genes, while suppressing LRR protein 66, Hsc70, BTB/POZ-TAZ, polygalacturonase, and expansins, indicating maintenance of cell wall integrity during TMV infection. RT-qPCR confirmed these results. In conclusion, Mikanolide enhances tobacco's resistance to TMV by inhibiting viral replication and proliferation and activating the plant's disease resistance signaling.