Intracellular localization and movement phenotypes of Alfalfa mosaic virusmovement protein mutants

Thirteen mutations were introduced in the movement protein (MP) gene of Alf alfa mosaic virus (AMV) fused to the green fluorescent protein (GFP) gene a nd the mutant MP-GFP fusions were expressed transiently in tobacco protopla sts, tobacco suspension cells, and epidermal cells of tobacco leaves. In ad dition, the mutations were introduced in the MP gene of AMV RNA 3 and the m utant RNAs were used to infect tobacco plants. Ten mutants were affected in one or more of the following functions of MP: the formation of tubular str uctures on the surface of protoplasts, association with the endoplasmic ret iculum (ER) of suspension cells and epidermal cells, targeting to punctate structures in the cell wall of epidermis cells, movement from transfected c ells to adjacent cells in epidermis tissue, cell-to-cell movement, or long- distance movement in plants. The mutations point to functional domains of t he MP and support the proposed order of events in AMV transport. Studies wi th several inhibitors indicate that actin or microtubule components of the cytoskeleton are not involved in tubule formation by AMV MP. Evidence was o btained that tubular structures on the surface of transfected protoplasts c ontain ER- or plasmalemma-derived material.