Expression of thePeanut stunt virusCoat Protein Gene Is Essential and Sufficient for Production of Host-Dependent Ribbon-Like Inclusions in Infected Plants

We previously have reported that infection of tobacco protoplasts or leaf tissue with the cucumovirus Peanut stunt virus (PSV) induced the production of unusual cytoplasmic ribbon-like inclusions. The formation of these novel inclusions is strain-specific, because infection of tobacco with subgroup II PSV strains, but not subgroup I strains, induced the production of inclusions. Furthermore, we have demonstrated that induction of the ribbon-like inclusions maps to PSV subgroup II RNA3, which codes for the coat protein (CP) and movement protein (MP). We have now extended these studies using chimeric constructs containing CP and MP open reading frames (ORFs) from PSV strains ER and W that belong to subgroups I and II, respectively. Additionally, recombinant Potato virus X (PVX) vectors containing translatable and untranslatable PSV CP ORF were constructed. Plants inoculated with infectious chimeric PSV or recombinant PVX transcripts were analyzed for CP expression by enzymelinked immunosorbent assay and reverse transcription-polymerase chain reaction and for inclusion production by electron microscopy. The results of these experiments indicated that translation of the CP ORF alone is essential and sufficient for inclusion production. In immunogold labeling experiments using an antiserum to PSV virions, abundant gold labeling of the inclusions was observed, suggesting that PSV CP is probably a major component of the inclusions. Because inclusion production is host specific, a host factor is likely to be involved. In addition to their diagnostic importance, these novel inclusions may also prove valuable in identifying the host factors that interact with PSV CP.