A viral protein activates MAPKs pathway to promote viral infection by downregulating callose deposition in plants

Abstract

Mitogen-activated protein kinase (MAPK) cascades are evolutionarily conserved in both plants and animals, playing critical roles in activating innate immunity to defend against various pathogens. However, the role of MAPK cascades in positively regulating or enhancing virus infections has not been extensively studied. In this study, we investigated the involvement of MAPK cascades in the infection of the positive-RNA virus, tomato chlorosis virus (ToCV), for the first time. Our findings reveal that ToCV infection activates MAPK cascades, promoting the virus spread within the plant. Specifically, ToCV P7, a pathogenicity determinant protein, localizes to the plasma membrane and recruits NbMPK3 from nucleus. Subsequently, P7 is directly phosphorylated on serine 59 by NbMPK3. The phosphorylated P7 then targets a remorin protein NbREM1, inhibiting callose deposition at plasmodesmata. These results demonstrate that conserved MAPK cascades directly phosphorylate viral proteins, modulating antiviral defense mechanisms by downregulating callose deposition at plasmodesmata and thereby enhancing virus transmission in plants. This study unveils molecular events associated with plasma membrane nanodomains and sheds light on the intricate arms race between host defense and viral counter-defense strategies.