Movement profiles: a tool for quantitative analysis of cell-to-cell movement of plant viral movement proteins

Movement proteins (MPs) are virally encoded factors that mediate transport of viral nucleic acid between plant cells. Many MPs are able to move between cells themselves. This feature serves as the basis for evaluation of the transport activity of individual MPs. MPs are transiently expressed as a fusion to autofluorescent proteins such as green fluorescent protein (GFP) in individual epidermal cells of leaves by biolistic delivery. Expressing cells can be directly monitored for subcellular localization and cell-to-cell movement of the MP:GFP fusion protein into neighboring cells by confocal scanning microscopy. During the time frame of transient expression, numerous cells are evaluated at several time points, and the accumulated data are depicted in a graph termed "movement profile." Thus, a movement profile will provide information on the correlation between subcellular localization of the MP in the expressing cell and the efficiency of cell-to-cell transport, the time course and efficiency of targeting of the MP to plasmodesmata, and the translocation efficiency of the MP into neighboring cells.