Although nanomaterials (NMs) may inhibit viral pathogens, the mechanisms governing plant-virus-nanomaterial interactions remain unknown. Nicotiana benthamiana plants were treated with nanoscale titanium dioxide (TiO) and silver (Ag), C fullerenes, and carbon nanotubes (CNTs) at 100, 200 and 500 mg L for a 21-day foliar exposure before inoculation with GFP-tagged tobacco mosaic virus (TMV). Plants treated with CNTs and C (200 mg L) exhibited normal phenotype and viral symptomology was not evident at 5 days post-infection. TiO and Ag failed to suppress viral infection. RT-qPCR analysis revealed that viral coat protein transcript abundance and GFP mRNA expression were reduced 74-81% upon CNTs and C treatment. TEM revealed that the chloroplast ultrastructure in carbon NM-treated plants was unaffected by TMV infection. Fluorescence measurement of CNTs and C (200 mg L) treated plants indicated photosynthesis equivalent to healthy controls. CNTs and C induced upregulation of the defense-related phytohormones abscisic acid and salicylic acid by 33-52%; the transcription of genes responsible for phytohormone biosynthesis was elevated by 94-104% in treated plants. Our findings demonstrate the protective role of carbon-based NMs, with suppression of TMV symptoms via hindered physical movement and viral replication. Given the lack of viral phytopathogen treatment options, this work represents a novel area of nano-enabled agriculture.
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