Figure 1 Morphology of ascovirus virions. (A) Schematic illustration of the structure of a typical ascovirus virion. The virion consists of an inner particle and an outer envelope. The inner particle is complex and contains a DNA/protein core surrounded by an apparent unit membrane, the external surface of which bears a layer of distinctive protein subunits. (B,C) Respectively, ultrathin longitudinal- and cross-sections through typical ascovirus virions. The dense inner layer corresponds with the distinctive layer of subunits shown in top left. (D) Negatively stained preparations of virions from isolates of three different ascovirus species: top right, Spodoptera frugiperda ascovirus 1a (SfAV-1a); E, Trichoplusia ni ascovirus 2a (TnAV-2a), and (F), Heliothis virescens ascovirus 3a (HvAV-3a). The reticulate appearance of the virion is thought to be due to the superimposition of top and bottom layers of the inner particle and outer envelope. The bar represents 50 nm.
Figure 2 Phylogenetic relationships within the family Ascoviridae. Consensus neighbor-joining trees (PHYLIP) were constructed using alignments of ascovirus DNA polymerase and major capsid protein sequences. Trees were rooted using corresponding sequences from the Chilo iridescent virus type 6 (CIV) and DpAV4a. Bootstrap values are shown at branch nodes in the trees and branch lengths are proportional to genetic distances. In shaded boxes are located a lineage of ascovirus that were previously considered as different species but which, in the light of the most recent data, belong to a master species in which some features, such as the presence of occlusion bodies, can vary significantly.
Figure 3 Synthesis of the evolutionary relationships among various genera of Mimiviridae (brown), Phycodnaviridae (green), Iridoviridae (invertebrate genera are in blue and vertebrate genera in dark blue), Ascoviridae (red) and DpAV4a (purple). The name of the principal virus representative of each genus is indicated. This synthetic tree was determined from results obtained with analyses of the 28 core genes. Plain lines represent verified relationships. Dotted lines indicate (putative) evolutionary pathways among virus families that require further support for confirmation. Phylogenetic analyses of major capsid protein (MCP) sequences revealed that at least three groups (G1, G2, G3) occurred within the iridovirus genus. A hypothetical fourth one, G4, was used to suggest the putative origin of the Ascoviridae.