Function of microtubules in intercellular transport of plant virus RNA

Cell-to-cell progression of tobacco mosaic virus (TMV) infection in plants depends on virus-encoded movement protein (MP). Here we show that a conserv ed sequence motif in tobamovirus MPs shares similarity with a region in tub ulins that is proposed to mediate lateral contacts between microtubule prot ofilaments. Point mutations in this motif confer temperature sensitivity to microtubule association and viral-RNA intercellular-transport functions of the protein, indicating that MP-interacting microtubules are functionally involved in the transport of vRNA to plasmodesmata. Moreover, we show that MP interacts with microtubule-nucleation sites. Together, our results indic ate that MP may mimic tubulin assembly surfaces to propel vRNA transport by a dynamic process that is driven by microtubule polymerization.