A receptor-like kinase controls plasmodesmal transport of conserved 30K viral movement proteins through phosphorylation

Intercellular viral movement in plants is mediated by movement proteins (MPs) that modulate plasmodesmata (PD) enabling cell-to-cell and systemic trafficking. Although phosphorylation has long been implicated in the regulation of MP localization and activity, the identity of host kinases and the interface with immune signaling have remain unresolved. Here, we identified the Arabidopsis thaliana lectin receptor-like kinase RDA2 as a PD-associated regulatory component of viral movement. Using proximity labeling, we detected RDA2 as a proximal interactor of the tobacco mosaic virus (TMV) MP, and show that RDA2 directly phosphorylates MP at multiple sites in vitro . Phosphorylation at threonine 75 is required for efficient PD targeting and intercellular movement, while phospho-dead mutants failed to complement viral spread. Loss of RDA2 enhanced MP mobility and increased TMV accumulation in planta , indicating that RDA2 modulates PD transport during the infection. RDA2 also interacted with and phosphorylated the movement protein of cucumber mosaic virus, implicating that this regulatory mechanism extends across members of the 30K MP superfamily. Our findings demonstrate that a plasma membrane receptor-like kinase can directly modify viral movement proteins, establishing a mechanistic link between receptor-mediated immune signaling and the post-translational control of symplasmic connectivity. One-sentence summary RDA2, a lectin receptor-like kinase, directly phosphorylates conserved 30K viral movement proteins to control their plasmodesmal targeting and restrict cell-to-cell viral spread in plants