Attenuation of cell-cell movement of tobamoviruses by the C-terminal GPI signal peptide of arabinogalactan protein FLA8

Plant viruses infect a wide range of plants and cause great economic losses worldwide every year. Following initial inoculation, plant viruses move cell to cell and systemically to establish systemic infection, whereas the host plant attempts to counteract these processes and restrict infection. Here, we identify a fasciclin-like glycosylphosphatidylinositol (GPI)-anchored arabinogalactan protein, FLA8, in Arabidopsis thaliana that functions in attenuating cell-to-cell movement of tobamoviruses. FLA8 interacts with the movement protein (MP) of turnip vein-clearing virus (TVCV) and restricts its ability to move between cells. Interestingly, the hydrophobic C-terminal GPI signal peptide (GPIsp) of FLA8 is necessary and sufficient for its interaction with MP and for movement suppression, suggesting that GPIsp domains of plant GPI-anchored proteins, once released from the rest of the protein molecule, can fulfill independent biological functions. FLA8 also restricts the cell-to-cell movement of tobacco mosaic virus (TMV) MP, highlighting a potential role for FLA8 in anti-tobamoviral defense.