Production of infectious in vitro transcripts from a full-length clover yellow mosaic virus cDNA clone

A full-length cDNA copy of clover yellow mosaic virus (CYMV) RNA was constructed from two smaller cDNA clones. In vitro transcription of linearized plasmid with T7 RNA polymerase produced genomic-sized RNA. These transcripts caused symptoms typical of CYMV infection when used to inoculate both a systemic host (Vicia faba) and a local lesion host (Gomphrena globosa). Electron microscopy of extracts from individual local lesions revealed virus particles identical to native CYMV. Increasing the length of the poly(A) tail from 23 residues to 80 or to 135 residues increased the infectivity rate from 12% to 17% or to 35% that of native CYMV RNA, respectively.