Protection against tobacco mosaic virus infection in transgenic plants requires accumulation of coat protein rather than coat protein RNA sequences.

Transgenic tobacco plants which express a chimeric gene encoding the tobacco mosaic virus (TMV) coat protein (CP) and the TMV 3' untranslated region are protected against infection by TMV. In this study chimeric genes that encode the sequences representing the TMV CP subgenomic RNA, but do not produce protein (because of removal of the initiation codon), and RNA that lacks the tRNA-like sequence of the TMV 3' end were expressed in transgenic plants. Only plants that accumulated CP, regardless of the presence of absence of the 3' end of TMV-RNA, were protected against infection by TMV. The results indicate that the CP per se, rather than TMV RNA, is responsible for the resistance to infection by TMV. Furthermore, the degree of protection is dependent upon the level of accumulated CP.