The two satellite RNAs associated with CYMV infections were sequenced. The larger (sCYMV-L1) has only linear molecules 1145 nucleotides long, a poly(A) tail, a long open reading frame (ORF) coding for a protein of M~ 39636 resembling in composition those of other large nepovirus satellite RNAs, a 5' leader sequence of 16 nucleotides and a 3' non-coding region of 40 nucleotides. In vitro translation of sCYMV-L1 yielded a protein product with a size that corresponded to that predicted from the sequence. The smaller satellite (sCYMV-S1) is 457 nucleotides long, has no ORF of significant length and no in vitro messenger activity. Both linear and circular forms of this satellite RNA were detected in infected tissues.Comparison of the sCYMV-S 1 primary structure with the sequences of other small nepoviral satellites reveals large regions of homology. Analysis of the secondary structures derived from the sequences of the plus and minus strands suggests possible consensus sequences for their self-cleavage.
CARNA 5, the small cucummber mosaic virus-dependent replicating RNA which is the causal agent of lethal tomato necrosis disease, causes a drastic reduction of disease symptoms in at least two other plant species. Satellite-like RNA's associated with plant viruses have a disease-regulating function.
A benign viral satellite RNA, in combination with a mild strain of cucumber mosaic virus (CMV-S), was used as a “vaccine” or “preinoculum” to demonstrate the feasibility of protecting pepper (Capsicum annuum cv. California Wonder) and melon (Cucurbita melo cv. Janus des Canaries) against two severe CMV strains, CMV-D and CMV-16, in the final 2 years of a 4-year pilot field and greenhouse experiment. In the field, healthy pepper and melon seedlings challenged with CMV-D and CMV-16 reduced yields by 33 to 60%; CMV-S caused only limited yield reduction in pepper and had no effect on the yield of melon. Different time intervals between preinoculation of pepper and melon seedlings with CMV-S and challenge inoculation with the severe CMV strains were tested. All plants challenged 3 weeks after vaccination showed nearly complete protection from subsequent infection by severe strains. The yield from preinoculated and challenged pepper plants was 80% that of untreated plants, while the yield from preinoculated and challenged melon plants was increased slightly over the untreated control plants. The use of this technology for biological control of plant viruses is discussed.
Numerous field trials have indicated that the effectiveness of Bacillus thuringiensis var. israelensis (B.t.i.) is limited to a short distance in streams, but the reasons for loss of toxicity have not been identified. Two streams were treated with B.t.i. and experiments were conducted to monitor the transfer of B.t.i. toxicity from the channel water to different compartments within the stream. These compartments included benthic substrates such as sediments, periphyton covering bedrocks, vegetation (moss and grass), and water samples taken from hyporheic probes (15, 35, and 65 cm depth). B.t.i. toxic activity was measured using bioassays with mosquito neonate larvae. Results indicated that loss to the hyporheic zone accounted for a significant fraction of B.t.i. removal from the open-channel water. Additional losses were attributable chiefly to moss, but sediments may play an important role in filtering or retaining B.t.i. toxic particles.
A cucumber mosaic virus (CMV-Ix) from Ixora is unusual in that it does not support the accumulation of some well-characterized CMV satellite RNAs in plants. CMV-Ix can support a particular satellite RNA variant which causes lethal tomato necrosis when inoculated with other CMV strains but not when inoculated with CMV-Ix. This difference in ability to support accumulation of specific satellite variants is apparent even when their sequences differ by only 10 nucleotides. Electroporation of tomato protoplasts with combinations of CMV-Ix or CMV-1 RNA plus the same satellite variants showed similar differences in accumulation, indicating a defect in satellite RNA replication and not movement or encapsidation. Pseudorecombinant virus infections between CMV-1 and CMV-Ix indicated that the genomic determinants responsible for this phenotype reside on RNA 1 since only combinations with CMV-Ix RNA 1 failed to replicate satellite RNA. The complete genome of CMV-Ix was cloned, sequenced and compared with the genomes of other cucumoviruses. CMV-Ix is most similar in RNA and protein sequence to subgroup 1 CMV-Fny and CMV-Y but slightly less similar than they are to each other. CMV-Ix and all cucumovirus strains sequenced thus far share a domain in the 3' untranslated portion of their genomic RNAs in which 39 of 40 bases are completely conserved.
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