title: Mapping nucleotides in the 126-kDa protein gene that control the differential symptoms induced by two strains of tobacco mosaic virus.
abstract: The differential symptom determinants of the Holmes' masked (M) and U1 strains of tobacco mosaic virus previously were mapped to the 5'-coterminal open reading frame (ORF) encoding the 126-kDa protein and the N-terminal two-thirds of the 183-kDa protein. Both proteins influence viral RNA accumulation, but the function of, and impact on, symptom formation by large domains within the 126-kDa gene, which are not conserved with sequences in analogous ORFs from other related viruses, are unknown. In the current study, cDNA clones representing each strain (i.e., MIC-TMV and U1-TMV) were mutated in these nonconserved domains to further define the nucleotides responsible for mosaic symptom induction on Nicotiana tabacum. Progeny virus of a mutant containing only eight nucleotide substitutions from the MIC-TMV sequence to the U1-TMV sequence within the 126-kDa protein ORF of MIC-TMV induced U1-TMV-like symptoms. Single or multiple substitutions among these eight nucleotides further defined residues critical for symptom modulation. Complementary substitutions in the MIC-TMV and U1-TMV sequences did not always yield progeny virus that induced complementary visual symptoms. Progeny of some mutants contained second-site spontaneous mutations at specific positions shown to influence symptom phenotype. For a subset of the stable site-directed mutants, there was no correlation between severity of systemic symptoms and chlorotic lesion size or virus accumulation in these chlorotic lesions on inoculated leaves.
authors.affiliation: Samuel Roberts Noble Foundation, Plant Biology Division, Ardmore, Oklahoma 73402, USA.
authors.forename: M H
authors.initials: MH
authors.lastname: Shintaku
authors.forename: S A
authors.initials: SA
authors.lastname: Carter
authors.forename: Y
authors.initials: Y
authors.lastname: Bao
authors.forename: R S
authors.initials: RS
authors.lastname: Nelson
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D002874:Chromosome Mapping; D004279:DNA, Viral; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D016366:Open Reading Frames; D010947:Plants, Toxic; D014026:Nicotiana / Q000821:virology; D014027:Tobacco Mosaic Virus / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity; D014764:Viral Proteins / Q000235:genetics* / Q000502:physiology
chemical_list: D004279:DNA, Viral; D014764:Viral Proteins