Abstract:Some plant virus encoded proteins contain nuclear localization signals (NLS) or nuclear export signals (NES) that mediate nucleo-cytoplasmic transport by three types of transport proteins: nuclear import proteins, nuclear export proteins and nucleo-cytoplasmic shuttling proteins. Virus proteins containing classical NLS are imported into the nucleus by recognizing the host nuclear transport receptors Importin α and Importin β, whereas the XPO1 protein mediates leucine-rich NES-dependent protein to export from the nucleus by involvement of the host Ran protein. The plant virus nucleo-cytoplasmic transport proteins get in and out of the nucleus to regulate biological functions through the host transport mechanism. Such functions include meditating nuclear import and export of the viral genome, local and long-distance virus movement, resisting host-induced RNA silencing, controlling virus replication and expression, regulating transcriptional activity of host cells and development of the disease phenotype. This review presents an overview of research advances in nucleo-cytoplasmic transport of plant virus proteins. We have mainly focused on types of nucleo-cytoplasmic transport proteins and their NLS and NES motifs, mechanisms of action and biological significance, and the host protein- mediated interactions.