Together with movement protein P3a, facilitates long-distance movement of virions in host (PubMed:30373157). Transports viral genome to neighboring plant cells directly through plasmosdesmata, without any budding (Probable). The movement protein allows efficient cell to cell propagation, by bypassing the host cell wall barrier (Probable). Binds ssRNA (By similarity). Homodimer (PubMed:30373157). Heterodimer with movement protein P3a (PubMed:30373157). Localizes to secondary branched plasmodesmata in source organs. Targeted to plasmodesmata in an actin- and endoplasmic reticulum-Golgi-dependent manner (By similarity). P3a directs P17 to the mitochondrial outer membrane while P17 regulates the localization of the P3a-P17 heterodimer to plastids (PubMed:30373157). The N-terminus is involved in homodimerization (By similarity). The C-terminus binds ssRNA (By similarity). The C-terminus is phosphorylated (By similarity). Expressed as a nonphosphorylated 20kDa form and a phosphorylated 22kDa form (By similarity). Phosphorylated by a host PKC-related kinase (By similarity). Serine phosphorylation is required for plamodesma targeting (By similarity). Poleroviruses are transmitted by aphids directly into phloem tissue. The virus replicates most efficiently in phloem companion cells and then moves through plasmodesmata between companion cells or into sieve elements for long distance transport. Belongs to the polerovirus movement protein family.