A dual-function movement protein regulates viral replication suppression and movement facilitation in plant viral infections

Viral replication and intracellular movement are essential and interdependent steps during plant viral infections. Mechanistic insights into each step have been established, but the regulatory interplay between these processes and their underlying molecular mechanisms remains poorly understood. Here, we observed the P4 movement protein (MP) of pod pepper vein yellows virus (PPeVYV), which represents the smallest identified member of the 30K movement protein superfamily, in Nicotiana benthamiana plants. Notably, P4 is recruited from the cytoplasm to plasmodesmata (PD) by components of the viral replication complexes (VRCs) that include P1, the P1-P2 fusion protein (P1P2), and viral RNA in a process that is mediated by P4 interacting with the C-terminal domain of P1P2 (P1P2C) during virus infection. The intracellular movement of P4 and the VRC depends on the endoplasmic reticulum (ER) and microfilaments, which are propelled by the myosin motors VIII-B and XI-K. Interestingly, the inhibitory function of P4 on viral replication is mediated by the specific recognition and degradation of viral RNA. Collectively, our data suggest a regulatory paradigm in which P4 orchestrates the spatiotemporal transition from viral genome replication to intracellular movement.