Genome structure of tobacco rattle virus strain PLB: further evidence on the occurrence of RNA recombination among tobraviruses.

RNA-2 (2196 nucleotides) of tobacco rattle virus (TRV) strain PLB was found to consist of a 5'-terminal sequence of 1376 nucleotides identical to the 5'-sequence of RNA-2 of TRV strain PSG and a 3'-terminal sequence of 820 nucleotides that is identical to the 3'-sequence of RNA-1 of strain PLB. Thus, in strains PLB and PSG the same coat protein gene is fused to different RNA-1 derived 3'-termini. By combining RNA-1 of TRV strain TCM with RNA-2 of strain PLB, a viable pseudo-recombinant was formed with genome segments that have nonidentical 3'-sequences. After 25 passages in tobacco each RNA retained its strain-specific 3'-sequences. This indicates that the perfect 3'-homology that occurs between the two genome segments of all natural TRV isolates analyzed so far is not a prerequisite for a stable genotype.