THE COWPEA MOSAIC-VIRUS M-RNA-ENCODED 48-KILODALTON PROTEIN IS RESPONSIBLE FOR INDUCTION OF TUBULAR STRUCTURES IN PROTOPLASTS

Tubular structures extending from plasmodesmata in cowpea mosaic virus (CPMV)-infected tissue have been implicated to play an important role in cell-to-cell movement of this virus. Using a cauliflower mosaic vi rus 35S promoter-based transient expression vector, we show that expre ssion of only the CPMV M RNA-encoded 48-kDa protein (48K protein) in c owpea protoplasts is sufficient to induce these structures. Strikingly , expression of the 48K protein in protoplasts from a number of nonhos t plant species, such as barley, Arabidopsis thaliana, and carrot, als o resulted in tubular structure formation. Thus, it is not likely that the viral 48K protein, though playing a key role in cell-to-cell move ment of CPMV, has a role in determining the host range of CPMV.