Characterization of a specific interaction between IP-L, a tobacco protein localized in the thylakoid membranes, and Tomato mosaic virus coat protein.

We previously demonstrated a specific interaction between Tomato mosaic virus (ToMV) coat protein (CP) and a tobacco protein designated IP-L that may be involved in the long-distance movement of ToMV. Here, using the yeast two-hybrid system and GST pull-down assay, we demonstrated that the N-terminal helical region (residues 3-18) of IP-L is required for the interaction, while two alpha-helical domains (residues 21-31 and 142-147) of ToMV CP are involved. Furthermore, using immunoblotting, we showed that both of the IP-L and the majority of ToMV CP are co-localized in the chloroplast thylakoid membranes. These results provide further evidence for the association between tobamovirus CPs and thylakoid membrane components, which has been shown to be involved in chlorosis formation during viral infection, and indicate that the interaction between ToMV CP and IP-L may affect chloroplast function and stability and thus leading to chlorosis.