Viral effector suppresses MTA/MTB-mediated m⁶A modification of genomic RNAs of a plant virus to facilitate infection.

N⁶-methyladenosine (m⁶A) is a prevalent dynamic RNA epigenetic modification that plays a crucial role in plant defense against viral infection. However, whether viruses have evolved mechanisms to counteract the m⁶A-associated defense remains unknown. Here, we report that a viral pathogen effector, the 2b protein encoded by cucumber mosaic virus (CMV), disables the methyltransferase of the m⁶A modification complex to evade the m⁶A-mediated plant defense. The viral effector 2b interacts with methyltransferase B (MTB), and this interaction re-localizes the MTA, the core component of the m⁶A methyltransferase, from the cytoplasm to the nucleus. The 2b protein not only prompts the MTA/MTB complex to form condensates in the nucleus but also inhibits their enzymatic activity, thereby suppressing m⁶A modification on the genomic/subgenomic RNAs of CMV to promote viral infection. Collectively, our findings uncovered a viral effector that targets and suppresses the m⁶A methyltransferase complex, shedding light on the mechanism by which plant viruses counteract m⁶A-mediated antiviral defense.