Evidence for a Satellite RNA Associated Naturally with the U5 Strain and Experimentally with the U1 Strain of Tobacco Mosaic Virus

Abstract

Isolates of tobacco mosaic virus strain U5 (TMV-U5) from native Nicotiana glauca plants induced the accumulation of a dsRNA (mol. wt 0.6 .times. 106) in infected plants that was more abundant than the replicative form (RF) dsRNA of TMV (mol. wt. 4.3 .times. 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 .times. 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 .times. 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 .times. 106 dsRNA. Plants infected with TMV-U5 isolates which did or did not induce the 0.6 .times. 106 dsRNA had identical symptoms. The host range of the 0.3 .times. 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 .times. 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 .times. 106 mol. wt. dsRNA and the 0.3 .times. 106 mol. wt. ssRNA found only in plants containing this dsRNA. The results indicate that the 0.6 .times. 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, but the nature of encapsidation of the satellite RNA has yet to be determined.