Cucumber mosaic virus movement protein modifies plasmodesmal function in transgenic melon plants

Most plant viruses encode a protein(s) essential for movement from the site of replication to surrounding, uninfected cells. These movement proteins (MPs) can interact with plasmodesmata (PD) to elicit an increase in the molecular size exclusion limit (SEL) from 1.0 kDa to values ranging from 10 to 30 kDa. In recent years, we have established that transgenic tobacco and potato plants expressing the MP of tobacco mosaic virus (TMV) have PD whose SELs are upregulated to more than 9.4 kDa. Interestingly, constitutive expression of the TMV-MP gene in these transgenic plants significantly affects carbon metabolism in source leaves and alters biomass distribution among the various plant organs, indicating that functional motifs on the MP alter carbohydrate translocation. In the present study, melon plants were transformed with the 3a gene product of cucumber mosaic virus (CMV). Expression of the 30-kDa protein in the transgenic plants was verified by western blot analysis. Dye-coupling technique was employed to examine the effect of this protein on plasmodesmal functioning. These studies established that the 30-kDa protein significantly increases the SEL of PD interconnecting the mesophyll cells of melon plants.