9β-Hydroxy-Ageraphoron Enhances TMV Resistance in Tobacco by Activating the SA Signaling Pathway through Upregulation of <i>MYB</i> and <i>DOF</i> Genes

Tobacco mosaic virus (TMV) poses a significant threat to global tobacco production. In this study, nine sesquiterpenoids isolated from <i>Ageratina adenophora</i> were evaluated for their anti-TMV activity using the half-leaf method. Among them, compound <b>1</b> (9β-hydroxy-ageraphorone) demonstrated the highest therapeutic (42.97%) and superior inactivation (48.87%) efficacy at 50 μg/mL. Further studies revealed that compound <b>1</b> disrupted TMV particle integrity and accelerated virion polymerization via hydrogen bonding and hydrophobic interactions with the viral coat protein. Additionally, it upregulated salicylic acid (SA) levels and enhanced the activities of PAL, POD, and SOD. Transcriptome and qRT-PCR analyses further indicated that compound <b>1</b> upregulated stress-responsive genes particularly <i>MYB</i> and <i>LBD</i> and activated the SA signaling pathway, leading to elevated expression of disease-resistant transcription factors and proteins, thereby enhancing TMV resistance in tobacco. These findings highlight 9β-hydroxy-ageraphorone as a promising candidate for botanical antiviral agents, contributing to the development of eco-friendly crop protection strategies.