Characterization of Tm-1 gene action on replication of common isolates and a resistance-breaking isolate of TMV.

Tm-1 is a gene which confers resistance to infection, in tomatoes, by tobacco mosaic virus (TMV). To investigate the biochemical mechanism of the resistance, we have established cell suspensions of three lines of tomatoes, i.e., +/+ (susceptible, wild-type, no Tm-1 gene), Tm-1/+ (heterozygous for the Tm-1 gene), and Tm-1/Tm-1 (homozygous for the Tm-1 gene). Protoplasts isolated from these cells were inoculated with RNA of the tomato strain L and Lta1 (a resistance-breaking strain which was recently isolated spontaneously from L) of TMV by means of electrophoration. The syntheses of all viral-coded proteins and TMV-specific RNAs could be detected in L-inoculated +/+ and Lta1-inoculated +/+, Tm-1/+, Tm-1/Tm-1 protoplasts, while their production was markedly reduced in L-inoculated Tm-1/+ protoplasts. L strain could multiply in Tm-1/+ protoplasts to a greater extent with less delay when a large amount of inoculum RNA was used. However, viral production was completely blocked in Tm-1/Tm-1 protoplasts even when a large amount of L-RNA was used for inoculation.