Evidence for a satellite RNA associated naturally with the U5 strain and experimentally with the U1 strain of tobacco mosaic virus
Summary Isolates of tobacco mosaic virus strain U5 (TMV-U5) from native Nicotiana glauca plants induced the accumulation of a dsRNA (mol. wt. 0.6 × 106) in infected plants that was more abundant than the replicative form (RF) dsRNA of TMV (mol. wt. 4.3 × 106). Some but not all subcultures of such a field isolate obtained from single local lesions on N. tabacum cv. Xanthi-nc, had lost the ability to induce the 0.6 × 106 mol. wt. dsRNA. Co-inoculation experiments in N. silvestris established that the dsRNA could accumulate in plants infected with TMV-U1, but to a lesser extent than when associated with TMV-U5. A ssRNA (mol. wt. 0.3 × 106) was isolated from plants containing the dsRNA. This was not infectious by itself but became so when associated with TMV-U5 or TMV-U1, and then induced the accumulation of the 0.6 × 106 dsRNA. Plants infected with TMV-U5 isolates which did or did not induce the 0.6 × 106 dsRNA had identical symptoms. The host range of the 0.3 × 106 ssRNA was the same as that of the TMV strain with which it was associated in each of the 20 experimental hosts tested. Complementary DNA transcribed from purified 0.6 × 106 dsRNA did not hybridize with RF and other dsRNAs of TMV-U5, TMV-U1, tobacco necrosis virus, potato virus X, citrus tristeza virus, and cucumber mosaic virus + CARNA 5, but the cDNA did hybridize with the 0.6 × 106 mol. wt. dsRNA and the 0.3 × 106 mol. wt. ssRNA found only in plants containing this dsRNA. The results indicate that the 0.6 × 106 dsRNA is the RF of a satellite RNA of TMV. Purified nucleoprotein from plants infected with TMV-U5 and the satellite RNA were infectious for the satellite RNA, but the nature of encapsidation of the satellite RNA has yet to be determined.