The 5 ' noncoding region of grapevine chrome mosaic nepovirus RNA-2 triggers a necrotic response on three Nicotiana spp.

The 5' noncoding region (NCR) of grapevine chrome mosaic nepovirus (GCMV) w as cloned in a viral vector derived from potato virus X (PVX), The recombin ant virus obtained was inoculated to Nicotiana benthamiana, N. clevelandii, and N, tabacum plants. Infected plants developed necrotic symptoms in plac e of the vein clearing and mosaic typically observed after inoculation with PVX. Northern (RNA) blot analysis showed that the replication of PVX was n ot specifically altered by the presence of the GCMV 5' NCR. Inoculation of recombinant PVX harboring deleted forms of the GCMV 5' NCR showed that the three stem-loop structures at the 3' end of the 5' NCR (nucleotides 153 to 206) are dispensable for the induction of necrosis. Further deletion analys is indicated that neither the 5'-most 70 nucleotides of the 5' NCR nor the downstream region (nucleotides 71 to 217) alone is able to induce the necro tic symptoms. In the presence of both the sequence encoding the GCMV coat p rotein and the GCMV 3' NCR, the GCMV 5' NCR failed to induce necrosis in th e PVX background. The mechanisms by which the expression of the 5' NCR migh t modify PVX symptoms are discussed.