A mutually antagonistic mechanism mediated by RNA m⁶A modification in plant-virus interactions.

Abstract

RNA-based immunity plays a central role in host defense against pathogens, with both hosts and pathogens continually evolving antagonistic strategies in their ongoing arms race. Although the presence of N6-methyl-adenosine (m⁶A) in viruses has been recognized for decades, its functional significance in plant antiviral defenses has only recently been revealed. Moreover, viral counterstrategies targeting m⁶A-mediated defenses remain largely unexplored. Here, we uncover a mutually antagonistic mechanism between m⁶A-mediated antiviral defense and a countermeasure employed by the RNA virus Cucumber mosaic virus (CMV). The deposition of m⁶A modification on CMV genomic RNAs was validated through m⁶A antibody-mediated MeRIP and nanopore-based direct RNA sequencing (DRS). During infection, plant m⁶A methyltransferases are translocated to the cytoplasm through their interaction with the viral coat protein (CP), facilitating viral m⁶A deposition. The plant EVOLUTIONARILY CONSERVED C-TERMINAL REGION 8 (ECT8) protein acts as a reader of viral m⁶A, destabilizing viral RNAs and mediating antiviral activity. Conversely, the CMV-2b protein, known as a viral suppressor of RNA silencing (VSR), antagonizes this defense by inhibiting viral m⁶A deposition. This occurs via direct interactions between 2b and the m⁶A methyltransferase components MTB and HAKAI, disrupting the methyltransferase complex's functionality. Furthermore, CMV-2b also downregulates global plant m⁶A levels, leading to the misexpression of defense-related transcripts. Collectively, our findings elucidate a previously unrecognized layer of host-virus interaction in which m⁶A modification serves as a regulatory battleground, positioning m⁶A dynamics as a new frontier in plant-virus coevolution.