Broad bean wilt virus 2 movement protein VP37 relocalizes the host co-chaperone HOP from the nucleus to plasmodesmata to promote viral intercellular movement

1. VP37 recruits NbHOP from the nucleus to plasmodesmata during BBWV2 infection. 2. NbHOP is essential for BBWV2 cell-to-cell movement and systemic spread in plants. 3. VP37 exploits the HSP90–HOP complex to stabilize MP folding and tubule formation. Plant viruses exploit host cellular machinery to fold, stabilize, and target their movement proteins (MPs) to plasmodesmata (PD), enabling viral cell-to-cell and systemic spread. In this study, we identified Nicotiana benthamiana HSP70–HSP90 organizing protein (NbHOP) as a proviral host factor that interacts with the Broad bean wilt virus 2 (BBWV2) MP, VP37. Yeast two-hybrid and co-immunoprecipitation assays revealed a specific interaction between VP37 and NbHOP. Subcellular localization analyses showed that NbHOP, which predominantly accumulates in the nucleus, is relocalized to PD upon co-expression with VP37 or during BBWV2 infection. Bimolecular fluorescence complementation confirmed that VP37 and NbHOP directly interact at PD. Domain mapping further demonstrated that the C-terminal region of TPR2B domain in NbHOP is required for VP37 binding. Functional assays demonstrated that NbHOP is essential for efficient BBWV2 infection: NbHOP silencing significantly reduced both systemic infection and cell-to-cell movement, whereas its overexpression enhanced viral cell-to-cell movement. Together with our previous finding that VP37 associates with HSP90, these results support a model in which VP37 co-opts the HSP90–HOP module to ensure proper folding, stabilization, and tubule formation at PD. This study uncovers an unrecognized role of HOP in plant–virus interactions and highlights the conserved HSP90–HOP chaperone complex as a key host machinery exploited for viral intercellular trafficking.