Isobavachalcone Alleviates Plant Photosynthesis Inhibition Caused by Tobacco Mosaic Virus (TMV) Infection in Tobacco

Viral infection affects photosynthesis in plants, significantly reducing crop yield and quality. This study investigated the effects of isobavachalcone (IBC), a natural compound extracted from the plant <i>Psoralea corylifolia</i> L., on photosynthesis in tobacco under tobacco mosaic virus (TMV; species <i>Tobamovirus tabaci,</i> family <i>Virgaviridae</i>) stress. TMV infection significantly reduced the chlorophyll content, Rubisco activity, net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO₂ concentration (Ci), and transpiration rate (Tr) in tobacco leaves. However, exogenous application of IBC (40 mg/L) effectively alleviated the negative impacts of TMV. Compared with the inoculated control, IBC treatment increased the chlorophyll content by 16.00-100.68%, enhanced Rubisco activity by 3.72-115.84%, and improved Pn, Gs, Ci, and Tr by 155.65-347.65%, 89.43-408.00%, 17.51-56.18%, and 106.76-336.80%, respectively, at 3-9 days post inoculation (dpi). Tandem massed tag-based quantitative proteomics analysis revealed that IBC upregulated the abundance of photosynthesis-related proteins, including those involved in photosystem II, cytochrome b6/f complex, photosystem I, and ATP synthase, under TMV infection. GO and KEGG enrichment analyses further confirmed that IBC enhanced the expression of proteins associated with photosynthesis and energy production pathways. These findings suggest that IBC can mitigate TMV-induced photosynthesis inhibition by increasing photosynthetic pigment content, promoting carbon assimilation, and regulating photosynthesis-related proteins, providing new insights into the molecular mechanism of IBC-mediated plant protection.