Evidence for an association between viral coat protein and host chromatin in mosaic-diseased tobacco leaves

The effect of infection with different viruses on the chromatin-associated protein constitution of young, developing tobacco leaves was investigated using SDS and two dimensional polyacrylamide gel electrophoresis. When systemic mosaic symptoms had developed, marked changes in the protein profile were evident. Tobacco mosaic virus (TMV) infection induced two additional protein bands with molecular masses of approximately -116 kD and 20 kD, respectively. Infection with a “green” isolate of cucumber mosaic virus (CMV) induced the formation of a single protein of about 28 kD, whereas the yellow strain P6 induced the formation of a slightly different protein of about 29 kD. The 20 kD protein induced by TMV was identified serologically as the virus coat protein, and the two CMV-induced proteins co-migrated with the coat proteins of the respective inducer strains. Virus infections resulting in necrosis, whether the virus remained localized in the inoculated leaves or became systemic, did not induce any changes in chromatin-associated proteins. Neither treatment with l-aminocyclocpropane-l-carboxylic acid, which induced premature senescence in young, developing leaves, nor natural senescence of old leaves oil flowering plants induced any changes comparable to TMV infection. Since purified TMV coat protein did not associate with chromatin upon incubation in vitro with nuclei from non-infected tobacco plants, the interaction of viral coat protein with host chromatin in infected plants is considered to be specific. The possibility that this association plays a role in symptom expression is discussed.