Recombination between genomic RNAs of two cucumoviruses under conditions of minimal selection pressure

Recombination is considered to play a key role in RNA virus evolution; however, little is known about its occurrence under natural conditions. We inoculated tobacco plants with wild-type strains of two closely related cucumovirus species; cucumber mosaic virus (CMV) and tomato aspermy virus (TAV). RNA from the inoculated leaves of doubly-infected plants was tested for the presence of recombination events in an 0.8-kb central portion of the viral RNA3. Using a sensitive and specific RT-PCR procedure, we amplified recombination segments of RNA3 in 3 of 82 tobacco plants infected with both viruses. In each plant in which recombinant segments were amplified, several different crossover, sites were observed, all of which were located within a short stretch of high sequence similarity. Two plants had both CMV-TAV and TAV-CMV recombinants. In all cases, precise homologous recombination had occurred. TO the best of our knowledge, this is the first report of interspecific recombination between wield-type plant RNA viruses under conditions of minimal selection pressure in favor of the recombinants. (C) 1999 Academic Press.