COAT PROTEIN-MEDIATED RESISTANCE IN TRANSGENIC TOBACCO EXPRESSING THE TOBACCO MOSAIC-VIRUS COAT PROTEIN FROM TISSUE-SPECIFIC PROMOTERS

Coat protein-mediated resistance (CP-MR) was studied in transgenic Nicotiana tabacum 'Xanthi nn' and 'Xanthi NN' that express chimeric tobacco mosaic virus (TMV) coat protein (CP) gene constructs using two different tissue-specific promoters. The Phaseolus vulgaris pal2 promoter leads to gene expression in the upper leaf epidermis and the xylem, while the rolC promoter from Agrobacterium rhizogenes leads to gene expression in phloem and leaf hair tip cells. Tissue-specific gene expression was verified using the gusA(uidA) reporter gene, while accumulation of TMV CP was verified by Western blot analysis. Transgenic Xanthi nn plants harboring the pal2-CP gene construct were partially resistant to TMV infection. On Xanthi NN plants that expressed the pal2-CP gene construct, fewer necrotic lesions were formed after TMV inoculation compared to nontransformed control plants. The level of resistance, however, was substantially less than in plant lines that expressed TMV CP from the cauliflower mosaic virus 35S promoter. By contrast, expression of the rolC-CP construct did not confer resistance in either Xanthi nn or Xanthi NN. The results provide further evidence that CP-MR to systemic TMV infection in tobacco is probably due to inhibition of infection rather than to effects on lang-distance spread through the phloem.