A receptor-like kinase links movement protein phosphorylation with immune regulation of plasmodesmata

Plasmodesmata integrate intercellular communication with immune regulation, but howreceptor-like kinase signalling is connected to viral movement protein control remainspoorly understood. Here, we identify the Arabidopsis lectin receptor-like kinase RDA2as a plasmodesmata-associated regulator of viral movement. RDA2 localizes toplasmodesmata-associated membrane sites, physically associates with movementproteins from tobacco mosaic virus and cucumber mosaic virus, and directlyphosphorylates them in vitro. Phosphorylation analysis of TMV MP identifies T75 as akey residue required for plasmodesmal targeting, intercellular movement andcomplementation of viral spread. In rda2 mutants, MP-dependent cell-to-cell movementand systemic TMV accumulation are enhanced. RDA2 is also required for poly(I:C)-induced plasmodesmal callose accumulation and immune marker gene activation,placing this kinase within a dsRNA-triggered pathway that controls symplasmicconnectivity. These findings identify RDA2 as a plasmodesmal immune kinase thatlinks inducible PD regulation with phosphorylation-dependent control of 30K movementproteins.