Characterization of Prunus-infecting apricot latent virus-like Foveaviruses: evolutionary and taxonomic implications.

The complete genomic sequences of four Prunus-infecting Apricot latent virus (ApLV) like isolates were determined and used to analyze the taxonomic position and variability of these viruses. The results indicate that all isolates show a typical Foveavirus genetic organization. Despite an average 23% nucleotide divergence, they show strong colinearity with only three regions of significant indel variability, in the internal and 3' non-coding regions and variable N-terminal half of the coat protein (CP). Sequence comparisons using the polymerase (Pol) and CP genes provide a conflicting taxonomic picture, with divergence level in the Pol and CP genes suggesting the existence of a single or of two species, respectively. However, a range of considerations argue that all four isolates should likely be considered as belonging to the ApLV species. ApLV is closely related to Apple stem pitting virus and could be considered a sister species to it, with ASPV being specialized to infect members of the Maloideae family and ApLV members of the Prunoideae. Analysis of selection pressures affecting the five open reading frames of ApLV and ASPV identified two regions under strong purifying selection, that coding for the conserved C-terminal half of the CP and the gene coding for the first protein of the triple gene block (TGBp1).