Biosynthesized silver nanoparticles mediated by Ammi visnaga extract enhanced systemic resistance and triggered multiple defense-related genes, including SbWRKY transcription factors, against tobacco mosaic virus infection

Abstract Background Tobacco mosaic virus (TMV) is a highly infectious plant virus that impacts a broad variety of plants and reduces crop yield around the world. Here, we assessed the effectiveness of using Ammi visnaga aqueous extract to synthesize silver nanoparticles (Ag-NPs) and their potential to combat TMV. Different techniques were used to characterize Ag-NPs, such as scanning and transmission electron microscopy (SEM, TEM), energy-dispersive X-ray spectroscopy (EDS), fourier transform infrared spectroscopy (FTIR), and dynamic light scattering (DLS). Results TEM demonstrated that the biosynthesized Ag-NPs had a spherical form with an average size of 25 nm. The zeta potential indicated the high stability of Ag-NPs, with a value of -15.9 mV. FTIR revealed various functional groups involved in the stability and capping of Ag-NPs. Interestingly, the Pre-treatment of tobacco plants (protective treatment) with Ag-NPs at 100 or 500 µg/mL significantly suppressed viral symptoms, while the Post-treatment (curative treatment) delayed their appearance. Furthermore, protective and curative treatments significantly increased chlorophyll a and b, total flavonoids, total soluble carbohydrates, and antioxidant enzymes activity. At the same time, it caused a drop in oxidative stress markers. The RT-qPCR results and volcano plots analysis showed that the Ag-NPs treatments triggers and regulates transcriptional of ten defense-related genes (SbWRKY-1, SbWRKY-2, JERF-3, GST-1, POD, PR-1, PR-2, PR-12, PAL-1, HQT-1). The heatmap revealed that GST-1, the primary gene involved in anthocyanidin production, was consistently the most expressed gene across all treatments throughout the study. Analysis of the gene co-expression network revealed that SbWRKY-19 was the most central gene among the studied genes, followed by PR-12 and PR-2. Conclusions Overall, the reported antiviral properties (protective and/or curative) of biosynthesized Ag-NPs against TMV lead us to recommend using Ag-NPs as a simple, stable, and eco-friendly agent in developing pest management programs against plant viral infections.