Cell-to-cell Movement of Plastids in Plants

Land plants developed highly sophisticated intercellular channels or plasmodesmata, which mediate cell-to-cell movement of nutrients, hormones and informa tunneling nanotubes, which were shown to mediate intercellular trafficking of organelles. Our objective was to test whether or not organelles move between cells in plants. As our experimental approach, we grafted two different species of tobacco, Nicotiana tabacum and Nicotiana sylvestris. Grafting triggers formation of new plasmodesmatal connections between the genetically distinct plants creating an opportunity for cell-to-cell organelle movement. We selected in tissue culture of the graft junctions for clonal lines, in which gentamycin resistance encoded in the N. tabacum nucleus was combined with spectinomycin resistance encoded in N. sylvestris plastids. Here we report cell-to-cell movement of the entire 161-kb plastid genome in these plants, most likely in intact plastids. We also report that the related mitochondria were absent, suggesting independent movement of the two DNA-containing organelles. Acquisition of plastids from neighboring cells provides a novel mechanism by which cells may be re-populated with functioning organelles. Our finding suggests a universal nature for intercellular organelle trafficking thus far documented only in mammalian cells and enables new biotechnological applications.