Exogenous Thiamine Regulates Multiple Plant Immunity-Associated Pathways to Inhibit MCMV Infection

Thiamine, also known as vitamin B1, serves as an inducer that strengthens plants and elicits defense responses to enhance resistance against pathogens. Currently, the antiviral mechanism of thiamine remains unclear. Here, we used maize chlorotic mottle virus (MCMV) as a model to elucidate the antiviral mechanism of thiamine. We found that thiamine application improved maize resistance to the MCMV. Transcriptome sequencing indicated that MCMV infection influenced the expression of thiamine synthesis pathway-related genes. Besides, MCMV P31 interacted with the key thiamine synthesis factor, ZmTHIC in cytoplasm, and blocked ZmTHIC entering into chloroplast. Using the cucumber mosaic virus (CMV) induced gene silencing system, we silenced ZmTHIC in maize, resulting in higher accumulation of MCMV compared to the control plants. LC-MS analysis revealed that both ZmTHIC silencing and MCMV infection reduced the thiamine content in maize. Thiamine treatment prior to MCMV infection enhanced plant defense responses by activating the MAPK pathway and promoting lignin synthesis in plant cell walls, ultimately inhibiting MCMV infection. Taking together, our results suggest that thiamine induced the synthesis of lignin and MAPK pathway to enhance the systemic immunity, promoting antiviral defense in maize. MCMV P31 hijacked ZmTHIC and prevented it from entering the chloroplasts, thereby inhibiting the synthesis of thiamine to dampen the synthesis of lignin and MAPK pathway to dampen the plant immunity. This research provides new insights into the antiviral mechanism of thiamine.