Poxvirus Host Range Genes and Virus-Host Spectrum: A Critical Review

Abstract

The Poxviridae family is comprised of double-stranded DNA viruses belonging to nucleocytoplasmic large DNA viruses (NCLDV). Among the NCLDV, poxviruses exhibit the widest known host range, which is likely observed because this viral family has been more heavily investigated. However, relative to each member of the Poxviridae family, the spectrum of the host is variable, where certain viruses can infect a large range of hosts, while others are restricted to only one host species. It has been suggested that the variability in host spectrum among poxviruses is linked with the presence or absence of some host range genes. Would it be possible to extrapolate the restriction of viral replication in a specific cell lineage to an animal, a far more complex organism? In this study, we compare and discuss the relationship between the host range of poxvirus species and the abundance/diversity of host range genes. We analyzed the sequences of 38 previously identified and putative homologs of poxvirus host range genes, and updated these data with deposited sequences of new poxvirus genomes. Overall, the term host range genes might not be the most appropriate for these genes, since no correlation between them and the viruses' host spectrum was observed, and a change in nomenclature should be considered. Finally, we analyzed the evolutionary history of these genes, and reaffirmed the occurrence of horizontal gene transfer (HGT) for certain elements, as previously suggested. Considering the data presented in this study, it is not possible to associate the diversity of host range factors with the amount of hosts of known poxviruses, and this traditional nomenclature creates misunderstandings.

Keywords: Poxviridae; evolution; horizontal gene transfer; host range genes; network.

Figure 1

Poxvirus host network. The poxvirus species and their hosts (taxonomic level of genus or higher) are depicted in the graph. The network layout was generated by applying a force-based algorithm, followed by manual rearrangement of the nodes. The full names of the viral species are listed in Supplementary Table S1.

Figure 2

Circos plot representing the amount and diversity of host range genes among the poxviruses. Genomic information was available at the NCBI database, following the established criteria (E-value ≤ 0.0001; Ident ≥ 30%; Coverage ≥ 40%). The different colors stand for the genus of poxviruses and the family of host range genes. The full names of the viruses are listed in Supplementary Table S1.

Figure 3

Presence of Ank-box host range gene projected onto a tree showing the phylogenetic relationships of representative poxvirus strains. The tree was generated from a multiple protein sequence alignment of the indicated sequences using the maximum likelihood method. A bootstrap of 1000 was used, and support >50 is indicated above the branches.

Figure 4

Phylogenetic relationship of p28-like genes. The tree was generated from a multiple protein sequence alignment of the indicated sequences using the maximum likelihood method. A bootstrap of 1000 was used, and support >50 is indicated above the branches.

Figure 5

Phylogenetic relationship of poxvirus B5R-related proteins. The tree was generated from a multiple protein sequence alignment of the indicated sequences using the maximum likelihood method. A bootstrap of 1000 was used, and support > 50 is indicated above the branches.