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Title:
'Evidence that a plant
virus switched hosts to infect a vertebrate and then recombined
with a vertebrate-infecting virus.'
(Full
paper - pdf format - available - click here)
Author: Gibbs MJ; Weiller GF
Address: Bioinformatics, Research School
of Biological Sciences, The Australian National University,
G.P.O. Box 475, Canberra 2601, Australia. mgibbs@rsbs.anu.edu.au
Source: Proc Natl Acad Sci USA,
96(14):8022-7 1999 Jul 6 Abstract
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 ourphylogenetic 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.
Explanitory extracts from paper:
'Sometimes viruses are transmitted to a host species that they have not previously infected or that they rarely infect. Several of these atypical interspecies transmission events (host-switching events) have led to disease outbreaks in this century (1-3).....similarities between the genomes of some plant-infecting, vertebrate-infecting, invertebrate-infecting, and microbe infecting viruses indicate that they have common ancestors (5), and suggest that at some point, ancestral viruses switched between these very different kinds of hosts. These more radical changes in host preference have led to the evolution of many new virus species. They are significant in terms of both disease and evolution; beyond that, little about them is known: neither the identity of the original hosts, nor the possibility of linkage between the change in host preference and a specific genetic change.
The history of viruses is further complicated by interspecies recombination. Distinct viruses have recombined with each other, producing viruses with new combinations of genes (6,7); viruses have also captured genes from their hosts (8,9).....
Interspecies recombination between viruses has been linked to disease outbreaks (10), and some analyses suggest that it may be linked to host-switching (7,11)....'
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