Satellite RNAs of Cucumber Mosaic Virus: Recombinants Constructed in Vitro Reveal Independent Functional Domains for Chlorosis and Necrosis in Tomato. Gael Kurath. Department of Plant Pathology, Cornell University, Ithaca, NY 14853 U.S.A. Peter Palukaitis. Department of Plant Pathology, Cornell University, Ithaca, NY 14853 U.S.A. . MPMI 2:91-96. Accepted 5 January 1989. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1989.

The biological activity of RNA transcribed from cDNA clones of three cucumber mosaic virus satellite RNAs was assessed in plants and found to correlate with the phenotype of the satellite RNA from which each clone was derived. Thus, transcript RNA of the D-sat, B-sat, and WL₁-sat clones all replicated well in tobacco, and induced necrosis, chlorosis, and amelioration, respectively, in tomato. To localize the satellite RNA domains responsible for symptom induction in tomato, we constructed six recombinant satellite RNA genomes in vitro from the infectious cDNA clones. Each recombinant contained a 185 nucleotide 5’ region and a 150 nucleotide 3’ region from different parental satellite RNA clones. Transcript RNA from each recombinant clone was infectious in tobacco, and replication in tomato induced symptoms that clearly demonstrated that the domain for chlorosis is in the 5’ 185 nucleotides, and the domain for necrosis is in the 3’ 150 nucleotides of the satellite RNA sequence. Analyses of amelioration in tomato indicated that this domain is more complex and will require further investigation. Characterization of the progeny satellite RNAs by RNA protection assays indicated that the recombinant genomes did not undergo major sequence alterations in the host species examined.