Transgenic plants that express the coat protein genes of tobacco mosaic virus or alfalfa mosaic virus interfere with disease development of some nonrelated viruses

Transgenic tobacco (Nicotiana tabacum 'Xanthi') plants that express the coat protein (CP) gene from the U₁ strain of tobacco mosaic virus (TMV) are resistant to infection by TMV. To determine whether these plants also are protected against other viruses, they were inoculated with low concentrations of potato virus X (PVX), potato virus Y (PVY), cucumber mosaic virus (CMV), alfalfa mosaic virus (AlMV), and the cowpea strain of TMV (Cc-TMV). Although the accumulation of virus in inoculated leaves was equivalent in plants that express the CP gene (CP+) and plants that do not express the CP gene (CP-), there was a delay of 1 to 3 days in the development of systemic disease symptoms on CP(+) plants infected with PVX, PVY, CMV, and A1MV as compared with CP(-) plants. The magnitude of protection, however, was significantly lower than against TMV. Protection against Cc-TMV, assayed on a CP(+) local lesion host, also was much lower than against TMV-U₁. A delay in disease development also was observed when transgenic tobacco (N. tabacum 'Samsun') plants expressing the CP gene of A1MV were infected with PVX and CMV, but not when they were infected with TMV-U₁. The results of these experiments demonstrate that transgenic tobacco plants that express different CP genes have a low but significant degree of protection against other viruses.