Infectious in vitro transcripts from cloned cDNA of a potyvirus, tobacco vein mottling virus

Full-length cDNA copies of tobacco vein mottling virus (TVMV) RNA were constructed downstream from bacteriophage T7 or T3 RNA polymerase promoters. The plasmids were designed to produce in vitro transcripts containing, respectively, one or two guanosine residues at the 5' terminus not derived from the TVMV sequence and a single cytidine residue at the 3' terminus following the poly(A) tail. Introduction of transcripts from either plasmid into tobacco mesophyll protoplasts resulted in the accumulation of TVMV coat protein and RNA. Neither coat protein nor viral RNA accumulated in protoplasts inoculated with linearized cDNA or with in vitro transcripts synthesized in the absence of 7-methylguanosine(5')triphospho(5')guanosine (m7GpppG). Tobacco seedlings inoculated with native TVMV RNA developed symptoms a few days before those inoculated with in vitro transcripts; however, 3 weeks after inoculation, the symptoms produced by the two inocula were indistinguishable.