Changes in locations of crossover sites over time in de novo generated RNA recombinants

Recombinant RNAs generated in plants 3 weeks postinoculation with turnip crinkle virus (TCV) genomic RNA and an associated satellite RNA, sat-RNA D, have a majority of TCV crossover sites in a 24-nucleotide repeat (motif IIIA/IIIB) that forms part of a stable hairpin (Carpenter et al., 1995, J. Mol.Biol. 245, 608-622). To determine if parameters other than nucleotide sequence in the crossover region affect junction site selection, recombinants were assayed at various times postinoculation of plants and protoplasts. Populations of recombinants became progressively shorter in plants and larger in protoplasts. Levels of inoculated transcript and age of the plant were not substantial factors in the shifts in crossover site locations. The two most commonly cloned recombinant species were not amplified to detectable levels in protoplasts, suggesting that these molecules are not viable templates for replication. These results suggest that recombination between sat-RNA D and TCV is a very frequent event, and populations of recombinants are likely generated de novo in each infected cell and represent the original recombinant molecules rather than progeny of such molecules. Therefore, factors other than simple selection for recombinants that are more fit to replicate are probably responsible for the differences in junction sites in populations of sat-RNA D/TCV recombinants.