Turnip mosaic virus co-opts host RNA methylation machinery to orchestrate plant infection

N6-methyladenosine (m ⁶ A) is a key RNA modification that regulates transcript stability and translation. However, its function in plant viruses remains largely unclear. Here, we show that the positive-sense single-stranded +ssRNA Turnip mosaic virus (TuMV) relies on the host m ⁶ A machinery to support efficient infection. Our findings uncover a previously unrecognized nuclear phase in the TuMV life cycle, during which viral RNA undergoes extensive methylation by host enzymes. We identify a complex and non-canonical methylation landscape on the TuMV genome, where canonical DRACH motifs are embedded within clusters of additional virus-specific non-canonical m ⁶ A sites. Notably, we also detect the presence of another RNA modification, m ⁵ C (5-methylcytosine), in close proximity to m ⁶ A-marked regions. This coordinated methylation landscape appears to be critical for efficient viral polyprotein synthesis. In its absence, the virus displays aberrant methylation and reduced infectivity as observed in m ⁶ A writer and reader mutants. Based on this, we propose a “seeding” model in which initial m ⁶ A deposition at canonical sites nucleates the formation of a broader network of m ⁶ A and m ⁵ C marks, likely guided by RNA structure rather than sequence motifs alone.