Frequent occurrence of recombinants in mixed infections of tomato yellow leaf curl disease-associated begomoviruses.

Begomoviruses are plant DNA viruses for which recombination plays a key role in driving evolution. However, little is known about how frequently begomovirus recombinants arise in mixed infected plants. To tackle this issue, co-infections of tomato with monopartite begomoviruses associated with the tomato yellow leaf curl disease, Tomato yellow leaf curl Sardinia virus and Tomato yellow leaf curl virus, have been studied as a model system. The frequency of recombinant genotypes in the progeny populations was evaluated at several times post inoculation. Recombinants constituted a significant proportion of the viral population. Interestingly, not all regions of the genome contributed equally to genetic exchange. In addition to the intergenic region, a known hot spot for recombination, a second hot spot region was found. Implication of secondary structure sequence features in cross-over sites is suggested, which might favor discontinuous DNA replication with the replication complex switching between homologous regions of DNA templates.