Recombination profiles between Tomato yellow leaf curl virus and Tomato yellow leaf curl Sardinia virus in laboratory and field conditions: evolutionary and taxonomic implications

Tomato yellow leaf curl Sardinia virus and Tomato yellow leaf curl virus have co-existed in Italiantomato crops since 2002 and have reached equilibrium, with plants hosting molecules of bothspecies plus their recombinants being the most frequent case. Recombination events are studiedin field samples, as well as in experimental co-infections, when recombinants were detected asearly as 45 days following inoculation. In both conditions, recombination breakpoints wereessentially absent in regions corresponding to ORFs V2, CP and C4, whereas density washighest in the 39-terminal portion of ORF C3, next to the region where the two transcription unitsco-terminate. The vast majority of breakpoints were mapped at antisense ORFs, supportingspeculation that the rolling-circle replication mechanism, and the existence of sense andantisense ORFs on the circular genome, may result in clashes between replication andtranscription complexes.