Analysis of the Complete Tomato Aspermy Virus Genomes Suggests Reassortment in Russian Isolates from Chrysanthemum

Tomato aspermy virus (TAV, genus Cucumovirus from the family Bromoviridae) is one of the most common and harmful chrysanthemum viruses, causing severe flower distortion, size reduction, and color breaking. Metatranscriptome sequencing of chrysanthemum plants of the Ribonette and Golden Standard cultivars from the collection of the Nikita Botanical Garden (Yalta, Republic of Crimea) generated TAV-related RNA reads. The complete genomes of two Russian isolates of the virus were assembled from the reads. This is the first report of full-length TAV genomes from Russia. Typically of cucumoviruses, the segmented TAV genome is represented by three single-stranded positive-sense linear RNA molecules of 3412 (RNA1), 3097 (RNA2) and 2219 (RNA3) nucleotides. Five open reading frames (ORF) have been identified that encode replicase (ORF1), RNA-dependent RNA polymerase (ORF2a), silencing suppressor protein (OFR2b), movement protein (OFR3a) and the coat protein (ORF3b). The identity of TAV genomes from the two chrysanthemum cultivars was 99.8% for all three viral RNAs; with other TAV isolates from GenBank it was 97.5-99.7% (RNA1), 93.8-99.8% (RNA2), and 89.3-99.3% (RNA3). Phylogenetic analysis showed that RNA1 and RNA3 of the Russian isolates were assigned to heterogeneous groups of TAV isolates found on various plant species in different regions of the world. At the same time, RNA2 clearly clustered with tomato isolates SKO20ST2 from Slovenia and PV-0220 from Bulgaria and, to a lesser extent, with the Iranian isolate Ker.Mah.P from petunia and the Chinese isolate Henan from chrysanthemum. The incongruence of phylogenetic trees reconstructed from different genome segments suggests pseudo-recombination (reassortment) in the Russian TAV isolates.

Automated summary

This study successfully assembled the complete genomes of two Russian isolates of TAV through metatranscriptome sequencing, and found differences between these isolates and TAV isolates from different regions of the world. Additionally, phylogenetic analysis showed incongruence between the phylogenetic trees reconstructed from different genome segments, suggesting the presence of pseudo-recombination.