Grapevine Fanleaf Nepovirus P38 Putative Movement Protein Is Located on Tubules In Vivo. Christophe Ritzenthaler. Institut de Biologie Moleculaire des Plantes du CNRS et Universite Louis Pasteur, Laboratoire de Virologie, 12 rue du General Zimmer, 67084 Strasbourg Cedex, France. Anne-Catherine Schmit, Pierre Michler, Christiane Stussi-Garaud, and Lothaire Pinck. Institut de Biologie Moleculaire des Plantes du CNRS et Universite Louis Pasteur, Laboratoire de Virologie, 12 rue du General Zimmer, 67084 Strasbourg Cedex, France. MPMI 8:379-387 . Accepted 31 January 1995. Copyright 1995 The American Phytopathological Society.

In Chenopodium quinoa cells infected with grapevine fan-leaf virus, tubular structures are formed which protrude from or penetrate the cell wall and which contain virus-like particles. These structures are thought to be involved in cell-to-cell spread of the virus. Immunogold cytochemistry using immunoaffinity-purified antibodies permitted the location of the P38 putative movement protein of grapevine fanleaf virus (GFLV) in or on these tubular structures. We have shown by light and electron microscopy that similar structures are formed at the surface of C. quinoa protoplasts, in the absence of cell wall and consequently of plasmodesmata. These tubules, although not abundant, measured 40 to 60 nm in diameter and up to 30 um in length. By immunofluorescence and immunogold-silver staining, P38 was localized along these structures. Together with P38 involvement in tubule formation in planta, this supports the idea that P38 protein has a role in the cell-to-cell spread of GFLV. These studies also revealed that P38 is very abundant in the cytoplasm of infected protoplasts. This subcellular location, although unusual for a movement protein, is, however, in agreement with previous subcellular fractionation experiments with P38 protein in C. quinoa plants.