Transgenic tobacco plants expressing the putative movement protein of tomato spotted wilt tospovirus exhibit aberrations in growth and appearance

Within the Bunyaviridae virus family, members of the genus Tospovirus are unique in their ability to infect plants. A characteristic genetic difference between tospoviruses and the animal-infecting members of this virus family is the occurrence of an additional gene, denoted NSM, located on the genomic M RNA segment. This gene has previously been implicated in the cell-to-cell movement of this virus during systemic infection. Transgenic tobacco plants have been obtained expressing the NSM protein of tomato spotted wilt virus (TSWV), the type member of the tospoviruses, from a constitutive promoter. Detectable amounts of the NSM protein could be observed in plants from nine different lines. The protein was only detectable in fractions enriched for cell wall material. More detailed immunogold labelling studies revealed specific association of NSM protein with plasmodesmata. Plants accumulating the NSM protein to detectable levels developed aberrations in growth, resulting in a significant reduction of size and accelerated senescence. In addition, these plants are restricted in their capacity to produce flowers. The results presented provide additional evidence that the NSM protein, by modifying plasmodesmata, represents the cell-to-cell movement function of tospoviruses. Furthermore, the phenotype of the NSM transgenic plants suggests involvement of the NSM gene product in TSWV symptom expression