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Nuclear exportin 1 facilitates turnip mosaic virus infection by exporting the sumoylated viral replicase and by repressing plant immunity.

Exportin 1/XPO1 is an important nuclear export receptor that binds directly to cargo proteins and translocates the cargo proteins to the cytoplasm. To understand XPO1 protein functions during potyvirus infections, we investigated the nuclear export of the NIb protein encoding the RNA-dependent RNA polymerase (RdRp) of turnip mosaic virus (TuMV). Previously, we found that NIb is transported to the nucleus after translation and sumoylated by the sumoylation (small ubiquitin-like modifier) pathway to support viral infection. Here, we report that XPO1 interacts with NIb to facilitate translocation from the nucleus to the viral replication complexes (VRCs) that accumulate in the perinuclear regions of TuMV infected cells. XPO1 contains two NIb-binding domains that recognize and interact with NIb in the nucleus and in the perinuclear regions, respectively, which facilitates TuMV replication. Moreover, XPO1 is involved in nuclear export of the sumoylated NIb and host factors tagged with SUMO3 that is essential for suppression of plant immunity in the nucleus. Deficiencies of XPO1 in Arabidopsis and Nicotiana benthamiana plants inhibit TuMV replication and infection. These data demonstrate that XPO1 functions as a host factor in TuMV infection by regulating NIb nucleo-cytoplasmic transport and plant immunity.