A tymovirus with an atypical 3'-UTR illuminates the possibilities for 3'-UTR evolution

We report the complete genome sequence of Dulcamara mottle virus (DuMV), confirming its membership within the Tymovirus genus, which was previously based on physical and pathology evidence. The 5'-untranslated region (UTR) and coding region of DuMV RNA have the typical characteristics of tymoviral RNAs. In contrast, the 3'-UTR is the longest and most unusual yet reported for a tymovirus, possessing an internal poly(A) tract, lacking a 3'-tRNA-like structure (TLS) and terminating at the 3'-end with -UUC instead of the typical -CC(A). An expressible cDNA clone was constructed and shown to be capable of producing infectious DuMV genomic RNAs with -UUC 3'-termini. A chimeric Turnip yellow mosaic virus (TYMV) genome bearing the DuMV 3'-UTR in place of the normal TLS was constructed in order to investigate the ability of the TYMV replication proteins to amplify RNAs with -UUC instead of -CC(A) 3'-termini. The chimeric genome was shown to be capable of replication and systemic spread in plants, although amplification was very limited. These experiments suggest the way in which DuMV may have evolved from a typical tymovirus, and illuminate the ways in which viral 3'-UTRs in general can evolve.