Evidence that a plant virus switched hosts to infect a vertebrate and then recombined with a vertebrate-infecting virus.
There are several similarities between the small, circular, single-stranded-DNA genomes of circoviruses that infect vertebrates and the nanoviruses that infect plants. We analyzed circovirus and nanovirus replication initiator protein (Rep) sequences and confirmed that an N-terminal region in circovirus Reps is similar to an equivalent region in nanovirus Reps. However, we found that the remaining C-terminal region is related to an RNA-binding protein (protein 2C), encoded by picorna-like viruses, and we concluded that the sequence encoding this region of Rep was acquired from one of these single-stranded RNA viruses, probably a calicivirus, by recombination. This is clear evidence that a DNA virus has incorporated a gene from an RNA virus, and the fact that none of these viruses code for a reverse transcriptase suggests that another agent with this capacity was involved. Circoviruses were thought to be a sister-group of nanoviruses, but our phylogenetic analyses, which take account of the recombination, indicate that circoviruses evolved from a nanovirus. A nanovirus DNA was transferred from a plant to a vertebrate. This transferred DNA included the viral origin of replication; the sequence conservation clearly indicates that it maintained the ability to replicate. In view of these properties, we conclude that the transferred DNA was a kind of virus and the transfer was a host-switch. We speculate that this host-switch occurred when a vertebrate was exposed to sap from an infected plant. All characterized caliciviruses infect vertebrates, suggesting that the host-switch happened first and that the recombination took place in a vertebrate.
Bioinformatics, Research School of Biological Sciences, The Australian National University, G.P.O. Box 475, Canberra 2601, Australia. mgibbs@rsbs.anu.edu.au
M J
MJ
Gibbs
G F
GF
Weiller
D000595:Amino Acid Sequence; D000818:Animals; D017925:Circovirus / Q000145:classification* / Q000235:genetics / Q000472:pathogenicity; D004265:DNA Helicases / Q000737:chemistry / Q000235:genetics*; D004268:DNA-Binding Proteins; D019143:Evolution, Molecular; D016679:Genome, Viral; D008969:Molecular Sequence Data; D010802:Phylogeny; D010942:Plant Viruses / Q000145:classification* / Q000235:genetics / Q000472:pathogenicity; D010944:Plants / Q000821:virology*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics*; D014714:Vertebrates / Q000821:virology*; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics*; D014779:Virus Replication
D004268:DNA-Binding Proteins; D015534:Trans-Activators; D014764:Viral Proteins; C045264:replication initiator protein; D004265:DNA Helicases