title: Infection of capilloviruses requires subgenomic RNAs whose transcription is controlled by promoter-like sequences conserved among flexiviruses.
abstract: The first open-reading frame (ORF) of apple stem grooving virus (ASGV), of the genus Capillovirus, encodes an apparently chimeric polyprotein containing conserved regions for replicase (Rep) and coat protein (CP). However, our previous study revealed that ASGV mutants with distinct and discontinuous Rep- and CP-coding regions successfully infect plants, indicating that CP expressed via a subgenomic RNA (sgRNA) is sufficient for viability of the virus. Here we identified a transcription start site of the CP sgRNA and revealed that CP translated from the sgRNA is essential for ASGV infection. We mapped the transcription start sites of both the CP and the movement protein (MP) sgRNAs of ASGV and found a hexanucleotide motif, UUAGGU, conserved upstream from both sgRNA transcription start sites. Mutational analysis of the putative CP initiation codon and of the UUAGGU sequence upstream from the transcription start site of CP sgRNA demonstrated their importance for ASGV accumulation. Our results also demonstrated that potato virus T (PVT), an unassigned species closely related to ASGV, produces two sgRNAs putatively deployed for the CP and MP expression and that the same hexanucleotide motif as found in ASGV is located upstream from the transcription start sites of both sgRNAs. This motif, which constituted putative core elements of the sgRNA promoter, is broadly conserved among viruses in the families Alphaflexiviridae and Betaflexiviridae, suggesting that the gene expression strategy of the viruses in both families has been conserved throughout evolution.
authors.affiliation: Laboratory of Plant Pathology, Department of Agricultural and Environmental Biology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Komatsu
authors.forename: Hisae
authors.initials: H
authors.lastname: Hirata
authors.forename: Takako
authors.initials: T
authors.lastname: Fukagawa
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Yamaji
authors.forename: Yukari
authors.initials: Y
authors.lastname: Okano
authors.forename: Kazuya
authors.initials: K
authors.lastname: Ishikawa
authors.forename: Tatsushi
authors.initials: T
authors.lastname: Adachi
authors.forename: Kensaku
authors.initials: K
authors.lastname: Maejima
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Hashimoto
authors.forename: Shigetou
authors.initials: S
authors.lastname: Namba
mesh_terms: D001483:Base Sequence; D027465:Chenopodium quinoa / Q000821:virology; D017124:Conserved Sequence; D052677:Flexiviridae / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification / Q000502:physiology*; D015967:Gene Expression Regulation, Viral; D016679:Genome, Viral; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000821:virology; D011401:Promoter Regions, Genetic; D012367:RNA, Viral / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D012367:RNA, Viral; D014764:Viral Proteins