Genetic Variability and Phylogeny of European mountain ash ringspot-associated virus RNA3 and RNA4

The European mountain ash ringspot-associated virus (EMARaV) is a multipartite RNA virus of negative polarity. It infects Sorbus aucuparia (common namerowan) trees throughout their whole distribution area in North and Central Europe. It causes mottling, chlorotic ringspots and decline of the whole plant. Infected rowans are serious virus sources for rowans and other potential hosts. EMARaV incidence and population structure was investigated in Germany, Finland, Sweden, Scotland, and Norway. Overall, EMARaV variants from 42 rowan trees distributed in 20 different locations were studied with regard to the genetic variability of the p3- and p4-coding genome region, as well as the 5 and 3 untranslated regions (UTR) of RNA3. In six of the 42 analyzed samples we found much higher sequence diversities than previously reported at the amino acid level in RNA3 encoded p3 protein sequences as well as at the nucleotide level on the 5 and 3 UTR. The other 36 EMARaV variants confirmed the assumed conservation of the nucleocapsid protein coding region. In contrast, the p4-coding genome region showed a high conservation of both nucleotide and amino acid sequences. Both EMARaV proteins were under strong purifying selection pressure, probably acting to maintain the functional integrity of the p3 and p4 proteins.