title: Asynchronous accumulation of lettuce infectious yellows virus RNAs 1 and 2 and identification of an RNA 1 trans enhancer of RNA 2 accumulation.
abstract: Time course and mutational analyses were used to examine the accumulation in protoplasts of progeny RNAs of the bipartite Crinivirus, Lettuce infectious yellow virus (LIYV; family Closteroviridae). Hybridization analyses showed that simultaneous inoculation of LIYV RNAs 1 and 2 resulted in asynchronous accumulation of progeny LIYV RNAs. LIYV RNA 1 progeny genomic and subgenomic RNAs could be detected in protoplasts as early as 12 h postinoculation (p.i.) and accumulated to high levels by 24 h p.i. The LIYV RNA 1 open reading frame 2 (ORF 2) subgenomic RNA was the most abundant of all LIYV RNAs detected. In contrast, RNA 2 progeny were not readily detected until ca. 36 h p.i. Mutational analyses showed that in-frame stop codons introduced into five of seven RNA 2 ORFs did not affect accumulation of progeny LIYV RNA 1 or RNA 2, confirming that RNA 2 does not encode proteins necessary for LIYV RNA replication. Mutational analyses also supported that LIYV RNA 1 encodes proteins necessary for replication of LIYV RNAs 1 and 2. A mutation introduced into the LIYV RNA 1 region encoding the overlapping ORF 1B and ORF 2 was lethal. However, mutations introduced into only LIYV RNA 1 ORF 2 resulted in accumulation of progeny RNA 1 near or equal to wild-type RNA 1. In contrast, the RNA 1 ORF 2 mutants did not efficiently support the trans accumulation of LIYV RNA 2. Three distinct RNA 1 ORF 2 mutants were analyzed and all exhibited a similar phenotype for progeny LIYV RNA accumulation. These data suggest that the LIYV RNA 1 ORF 2 encodes a trans enhancer for RNA 2 accumulation.
authors.affiliation: Department of Plant Pathology, University of California, Davis 95616, USA.
authors.forename: H H
authors.initials: HH
authors.lastname: Yeh
authors.forename: T
authors.initials: T
authors.lastname: Tian
authors.forename: L
authors.initials: L
authors.lastname: Rubio
authors.forename: B
authors.initials: B
authors.lastname: Crawford
authors.forename: B W
authors.initials: BW
authors.lastname: Falk
mesh_terms: D001483:Base Sequence; D019663:Chenopodiaceae; D017790:Closterovirus / Q000235:genetics*; D004279:DNA, Viral; D004742:Enhancer Elements, Genetic; D018545:Lactuca / Q000821:virology*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D012367:RNA, Viral / Q000378:metabolism*
chemical_list: D004279:DNA, Viral; D012367:RNA, Viral