VIRAL COAT PROTEIN IS TARGETED TO, BUT DOES NOT GATE, PLASMODESMATA DURING CELL-TO-CELL MOVEMENT OF POTATO-VIRUS-X

The coat protein (CP) of potato virus X was localized immunocytochemic ally in infected leaves of susceptible Nicotiana species and shown to be targeted to the central cavity of plasmodesmata in virus-infected c ells. A viral deletion mutant, in which the CP gene was replaced with the gene for the green fluorescent protein (GFP), was restricted to si ngle, inoculated cells. However, movement of the mutant virus was resc ued on transgenic plants constitutively expressing the CP gene, and th e CP was again targeted to plasmodesmata. The CP was not localized to plasmodesmata in uninfected transgenic plants and, in contrast to the plasmodesmata of PVX-infected cells, the plasmodesmata of the transgen ic plants did not allow the passage of 10 kDa fluorescent dextrans. We propose that the CP is not involved in plasmodesmal gating per se, bu t is necessary for transport of the viral RNA to, and possibly through , plasmodesmata.