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

A recombination event at the 3' end of RNA 3 in a pseudorecombinant virus (C1C2T3) having RNAs 1 and 2 from TrK7-cucumber mosaic virus (CMV) and RNA 3 from P-tomato aspermy virus (TAV) was detected by ribonuclease protection assay (RPA). Sequence analysis of the 3' end of RNA 3 of 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 derived 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 from CMV. The second one would have eliminated the TAV-derived sequences in this duplicated region. Competition experiments in tobacco plants showed that in a context of RNA 1 + 2 from CMV, RNA 3 from TAV is outcompeted 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 relative fitness associated with the recombinant nature of RNA 3. Our results document the potential importance of RNA-RNA recombination in the determination of the genetic structure of RNA viral populations. (C) 1994 Academic Press, Inc.