2 PROTEINS OF A PLANT DNA VIRUS COORDINATE NUCLEAR AND PLASMODESMAL TRANSPORT

Plant viruses establish a systemic infection by moving through plasmod esmata, but little is known of the mechanism(s) involved. The roles of two movement-associated proteins of a single-stranded DNA virus were investigated in vivo, using functional proteins expressed in E. coli a nd microinjection into plant cells. We report here that the all protei n of bean dwarf mosaic geminivirus moves extensively from cell to cell , increases mesophyll plasmodesmal size exclusion limit, and potentiat es the movement of double-stranded DNA from cell to cell. Movement of single and double-stranded DNA out of the nucleus is mediated by the B R1 protein. These results provide direct experimental evidence for int ercellular macromolecular transport in plants, and suggest that the BR 1 and BL1 proteins coordinate the movement of viral DNA across both nu clear and plasmodesmal boundaries.