Host adaptation and replication properties of two bipartite geminiviruses and their pseudorecombinants

To investigate factors involved in host adaptation and specificity of bipartite geminiviruses, the infectivity of bean dwarf mosaic (BDMV) and tomato mottle (ToMoV) geminiviruses and the BDMV/ToMoV pseudorecombinants [BDMV DNA-A + ToMoV DNA-B (BA+TB) and ToMoV DNA-A + BDMV DNA-B (TA+BB)] in Phaseolus vulgaris, Lycopersicon esculentum, Nicotiana benthamiana, and N. tabacum plants was determined. Additionally, replication of these viruses was examined in protoplasts prepared from N. tabacum BY2 and Xanthi-nc cells. In adapted hosts and the permissive experimental host, N. benthamiana, BDMV and ToMoV infected nearly 100% of inoculated plants, induced severe symptoms, and had high levels of both DNA components. In nonadapted hosts, BDMV and ToMoV infected approximately 40% of inoculated plants, induced no symptoms, and had reduced levels of both DNA components. For the pseudorecombinants, symptoms were observed only in TA+BB-infected N. benthamiana and P. vulgaris plants. In the other pseudorecombinant/host combinations, symptomless infections were detected and some plants were infected with the DNA-A component only. Symptom development and/or higher infection rates for the pseudorecombinants were correlated with the host-adapted DNA-B component, and pseudorecombinant-infected plants had reduced levels of DNA-B. Protoplast replication assays revealed inefficient DNA-B replication for the pseudorecombinants, and differences in viral replication properties in the two N. tabacum cell lines.