Ubiquitin-Conjugating Enzyme Positively Regulates Salicylic Acid and Jasmonic Acid Biosynthesis to Confer Broad-Spectrum Antiviral Resistance in Nicotiana benthamiana

Ubiquitin-conjugating enzyme (UBC) plays a significant role in plant hormone signal transduction. In this study, we observed that TuMV infection markedly upregulates UBC mRNA expression, suggesting a close association between UBC and viral infection. Using Tobacco rattle virus (TRV)-based virus-induced gene silencing (VIGS) to downregulate UBC expression in <i>Nicotiana benthamiana</i>, we found that UBC-silenced plants exhibited enhanced susceptibility to TuMV compared with control plants. Conversely, transient overexpression of UBC protein suppressed viral propagation. Further analysis by reverse transcription quantitative PCR (RT-qPCR) revealed a substantial downregulation in the expression of SA and JA biosynthetic genes in UBC-silenced plants. Accordingly, liquid chromatography-tandem mass spectrometry (LC-MS/MS) confirmed a marked decrease in the accumulation of the corresponding hormones. Exogenous application of SA or JA partially restored antiviral resistance in UBC-silenced plants, indicating that hormonal deficiency contributes to enhanced viral susceptibility. Collectively, our results demonstrate that UBC positively regulates SA and JA biosynthesis. UBC silencing impairs both SA- and JA-mediated defense pathways, thereby facilitating viral infection in <i>N. benthamiana</i>.