Coat proteins of necroviruses target 14-3-3a to subvert MAPKKKα-mediated antiviral immunity in plants.

Mitogen-activated protein kinase (MAPK) cascades play an important role in innate immunity against various pathogens in plants and animals. However, we know very little about the importance of MAPK cascades in plant defense against viral pathogens. Here, we used a positive-strand RNA necrovirus, beet black scorch virus (BBSV), as a model to investigate the relationship between MAPK signaling and virus infection. Our findings showed that BBSV infection activates MAPK signaling, whereas viral coat protein (CP) counteracts MAPKKKα-mediated antiviral defense. CP does not directly target MAPKKKα, instead it competitively interferes with the binding of 14-3-3a to MAPKKKα in a dose-dependent manner. This results in the instability of MAPKKKα and subversion of MAPKKKα-mediated antiviral defense. Considering the conservation of 14-3-3-binding sites in the CPs of diverse plant viruses, we provide evidence that 14-3-3-MAPKKKα defense signaling module is a target of viral effectors in the ongoing arms race of defense and viral counter-defense.