Tobacco mosaic virus particles uncoat and express their RNA in Xenopus laevis oocytes: implications for early interactions between plant cells and viruses.

Xenopus laevis oocytes were microinjected with tobacco mosaic virus (TMV) particles or unencapsidated TMV RNA at equivalent RNA concentrations. After a 5-hr incubation, batches of 10 oocytes from each treatment were frozen and lysed, and the supernatants were subjected to SDS-PAGE and Western immunoblotting with antiserum raised against a TMV RNA-encoded polypeptide of mol wt 126,000 (126K), purified from TMV-infected tobacco. Cross-reaction with a polypeptide of 126K synthesized in vitro, in a rabbit reticulocyte cell-free system programmed with TMV RNA, confirmed the specificity of the antiserum. Oocytes microinjected with TMV particles produced at least as much immunoreactive 126K protein as those injected with TMV RNA. We conclude that intact virus particles were disassembled, at least in part, to release some functional RNA within the cytoplasm of these animal cells. Hypotheses which postulate a specific role for cellulose cell walls, or the external surface of the plasmalemma, in virus disassembly seem unable to explain this observation. We favor an intracellular site and a more universal mechanism for ribonucleocapsid disassembly. This result may also affect our views on factors which determine the host range of plant viruses.