A plant RNA virus hijacks a dual-specificity phosphatase to attenuate MAPK-mediated immunity for robust infection

Mitogen-activated protein kinase (MAPK) cascades play vital roles in plant responses to biotic and abiotic stresses; however, their regulation during viral infection and the mechanisms by which viruses counteract these defenses remain poorly understood. Here, we report that the Arabidopsis thaliana atypical dual-specificity phosphatase (DSP) DSP4 negatively regulates plant immunity against turnip mosaic virus (TuMV), a member of the Potyviridae family. Subcellular localization, fractionation, and mutagenesis revealed that DSP4 is anchored to the cellular membrane via its C-terminus. Notably, only the membrane-bound form of DSP4 interacts with and dephosphorylates the MAPKs, MPK6 and MPK3, which redundantly restrict TuMV infection. Furthermore, TuMV P3 protein binds to DSP4, maintaining it on the membrane to dephosphorylate MPKs, whereas DSP4 is typically released from the membrane during immune priming. These findings unveil a molecular mechanism wherein TuMV P3 exploits this membrane-associated phosphatase to dampen MAPK-mediated immunity and promote virus infection.