EVOLUTION OF A QUADRIPARTITE HYBRID VIRUS BY INTERSPECIFIC EXCHANGE AND RECOMBINATION BETWEEN REPLICASE COMPONENTS OF 2 RELATED TRIPARTITE RNA VIRUSES

Cucumber mosaic virus (CMV) and tomato aspermy virus (TAV) belong to t he Cucumovirus genus. They have a tripartite genome consisting of sing le-stranded RNAs, designated 1, 2, and 3. Previous studies have shown that viable pseudorecombinants could be created in vitro by reciprocal exchanges between CMV and TAV RNA 3, but exchanges of RNAs 1 and 2 we re replication deficient, When we coinoculated CMV RNAs 2 and 3 along with TAV RNAs 1 and 2 onto Nicotiana benthamiana, a hybrid quadriparti te virus appeared that consisted of TAV RNA I, CMV RNAs 2 and 3, and a distinctive chimeric RNA originating from a recombination between CMV RNA 2 and the 3'-terminal 320 nucleotides of TAV RNA 2. This hybrid a rose by means of segment reassortment and RNA recombination to produce an interspecific hybrid with the TAV helicase subunit and the CMV pol ymerase subunit, To our knowledge, this is the first report demonstrat ing the evolution of a new plant or animal virus strain containing an interspecific hybrid replicase complex.