INCREASE IN THE RELATIVE FITNESS OF A PLANT-VIRUS RNA ASSOCIATED WITHITS RECOMBINANT NATURE

A recombination event at the 3' end of RNA 3 in a pseudorecombinant vi rus (C1C2T3) having RNAs 1 and 2 from TrK7-cucumber mosaic virus (CMV) and RNA 3 from P-tomato aspermy virus (TAV) was detected by ribonucle ase protection assay (RPA). Sequence analysis of the 3' end of RNA 3 o f C1C2T3 and of its parental CMV and TAV strains showed that RNA 3 of C1C2T3 had a hybrid nature in which most of the 3' noncoding region (3 ' ncr), including the whole 3' terminal tRNA-like structure, was deriv ed from CMV RNA 2 by recombination. Recombination may have occurred in two steps. The first one would have caused the duplication of a large region 5' to the 3' end tRNA-like structure, derived from TAV and fro m CMV. The second one would have eliminated the TAV-derived sequences in this duplicated region. Competition experiments in tobacco plants s howed that in a context of RNA 1 + 2 from CMV, RNA 3 from TAV is outco mpeted by RNA 3 of CMV, but the recombinant TAV RNA 3 with the 3' end of CMV outcompetes both TAV and CMV RNA 3. This shows an increase in r elative fitness associated with the recombinant nature of RNA 3. Our r esults document the potential importance of RNA-RNA recombination in t he determination of the genetic structure of RNA viral populations. (C ) 1994 Academic Press, Inc.