Synthesis of infectious transcripts of blueberry scorch carlavirus in vitro.

Blueberry scorch carlavirus (BBScV) is a filamentous virus with a polyadenylated, positive-sense RNA genome. A near full-length cDNA clone of BBScV was constructed by assembly of clones from a cDNA library. To generate a full-length cDNA clone, the 5' terminus was mutagenized by PCR to introduce nucleotides present in the wild-type virus and not in the near full-length clone, and then fused directly to the T7 bacteriophage RNA polymerase promoter at the 5' terminus. Capped and uncapped BBScV transcripts were synthesized in vitro from the full-length cDNA clone. Capped transcripts were infectious, producing systemic symptoms identical to those caused by the wild-type virus following inoculation onto Chenopodium quinoa leaves. Uncapped transcripts were substantially less infectious than capped transcripts. This represents the first report of infectious transcripts for a member of the carlavirus group.