UNUSUAL CYTOPLASMIC INCLUSIONS INDUCED IN TOBACCO BY PEANUT STUNT VIRUS SUBGROUP-II STRAINS MAP TO RNA3

Infection of tobacco protoplasts or leaf tissues with peanut stunt vir us (PSV) subgroup II strains induced the production of unusual cytopla smic ribbon-like inclusions. The inclusion structures appeared as long , thin, densely staining sheets that were prevalent within the cytopla sm, accumulating most commonly near vacuoles. Numerous virions and rib osomes could be seen adjacent to the inclusion surfaces. The formation of these novel inclusions appeared to be subgroup specific, since inf ection of tobacco with PSV strains W and B (subgroup II), but not stra ins ER, V, and J (subgroup I), induced the inclusions. Furthermore, in clusion formation was shown to be host specific, because the inclusion s were not detected in either of two leguminous host species infected with PSV subgroup II strains. Using tobacco protoplasts electroporated with various assortments of infectious RNA transcripts derived from c DNA clones of genomic RNAs of PSV-ER and PSV-W, we demonstrated that i nduction of the unusual ribbon-like inclusions maps to PSV-W (subgroup II) RNA3. This conclusion is consistent with the finding that PSV str ain BV-15, a natural intraspecific reassortant that derives its RNA2 a nd RNA3 from a subgroup I strain, did not induce inclusion formation.