An m6A methyltransferase confers host resistance by degrading viral proteins through ubiquitination

Posttranscriptional and posttranslational modifications play crucial roles in plant immunity. However, how plants fine-tune such modifications to activate antiviral immunity remains unknown. Here, we report that the m⁶A methyltransferase TaHAKAI is utilized by wheat yellow mosaic virus (WYMV) to increase viral genomic m⁶A modification and promote viral replication. However, TaHAKAI also functions as an E3 ligase that targets the viral RNA silencing suppressor P2 for degradation and inhibits viral infection. A major allele of TaHAKAI in a susceptible cultivar exhibited reduced E3 ligase activity but not m⁶A methyltransferase activity, promoting viral infection. Interestingly, TaHAKAI^R attenuates the stability of TaWPS1 (Wheat paired spikelets 1, WPS1) mRNA, the negative regulator of spike development, which might increase panicle length and spikelet number by modulating its m⁶A modification. Our study reveals a mechanism for balancing disease resistance and yield by fine-tuning m⁶A modification and ubiquitination.