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Molecular characterization of an unusual new plant RNA virus reveals an evolutionary link between two different virus families.

ABSTRACT: An unusual novel plant virus provisionally named goji berry chlorosis virus (GBCV) was isolated from goji berry plants (Lycium chinense Miller) showing chlorosis symptoms and its complete genome sequence was determined. The viral genome consists of a positive-sense single-stranded RNA of 10,100 ribonucleotides and contains six open reading frames (ORFs). Electron microscopy showed that the viral genome is packaged as a filamentous particle with an average length of approximately 850 nm. Phylogenetic analysis and amino acid similarity analysis of the encoded ORFs revealed that this new virus could be classified in an intermediate position between the families Benyviridae and Virgaviridae. The GBCV 200-kDa replicase (ORF1) is more similar to benyvirus replicases than to virgavirus replicases, while its 17-kDa coat protein (CP, ORF2) is more closely related with virgavirus CPs than benyvirus CPs. ORF3 was predicted to produce a C-terminally extended protein from ORF2 via frameshifting. While ORF4 (45-kDa), ORF5 (44-kDa), and ORF6 (16-kDa) have no apparent sequence homology with other known viruses, ORF5 is predicted to encode a movement protein (MP) that is phylogenetically related to the furovirus MP and ORF6 was experimentally proven to encode a viral suppressor of RNA silencing. These unusual characteristics suggest that GBCV may represent an evolutionary link between the families Benyviridae and Virgaviridae and indicate the existence of a novel, unidentified virus group.

SUBMITTER: Kwon SJ

PROVIDER: S-EPMC6197668 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The diversity of a highly variable RNA plant virus was considered to determine the range of virulence substitutions, the evolutionary pathways to virulence, and whether intraspecific diversity modulates virulence pathways and propensity. In all, 114 isolates representative of the genetic and geographic diversity of Rice yellow mottle virus (RYMV) in Africa were inoculated to several cultivars with eIF(iso)4G-mediated Rymv1-2 resistance. Altogether, 41 virulent variants generated from ten wild isolates were analyzed. Nonconservative amino acid replacements at five positions located within a stretch of 15 codons in the central region of the 79-aa-long protein VPg were associated with virulence. Virulence substitutions were fixed predominantly at codon 48 in most strains, whatever the host genetic background or the experimental conditions. There were one major and two isolate-specific mutational pathways conferring virulence at codon 48. In the prevalent mutational pathway I, arginine (AGA) was successively displaced by glycine (GGA) and glutamic acid (GAA). Substitutions in the other virulence codons were displaced when E48 was fixed. In the isolate-specific mutational pathway II, isoleucine (ATA) emerged and often later coexisted with valine (GTA). In mutational pathway III, arginine, with the specific S2/S3 strain codon usage AGG, was displaced by tryptophane (TGG). Mutational pathway I never arose in the widely spread West African S2/S3 strain because G48 was not infectious in the S2/S3 genetic context. Strain S2/S3 least frequently overcame resistance, whereas two geographically localized variants of the strain S4 had a high propensity to virulence. Codons 49 and 26 of the VPg, under diversifying selection, are candidate positions in modulating the genetic barriers to virulence. The theme and variations in the evolutionary pathways to virulence of RYMV illustrates the extent of parallel evolution within a highly variable RNA plant virus species.

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Molecular characterization of an unusual new plant RNA virus reveals an evolutionary link between two different virus families.

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