An m(6)A 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 m(6)A methyltransferase TaHAKAI is utilized by wheat yellow mosaic virus (WYMV) to increase viral genomic m(6)A 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 m(6)A 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 m(6)A modification. Our study reveals a mechanism for balancing disease resistance and yield by fine-tuning m(6)A modification and ubiquitination.