Specificity of bipartite geminivirus movement proteins

Pseudorecombinants produced by exchanging genome components (DNAs A and B) of the geminiviruses African cassava mosaic virus (ACMV) and Indian cassava mosaic virus (ICMV), ACMV, and tomato golden mosaic virus (TGMV), and TGMV and abutilon mosaic virus (AbMV) are not infectious in their common host Nicotiana benthamiana. In each case, DNA A was unable to trans-replicate the heterogenomic DNA B component in a N. benthamiana leaf disc assay. The non-viability of the pseudorecombinants has been exploited to investigate the specificity of geminivirus movement proteins, encoded by DNA B, by co-inoculating N. benthamiana with both genome components of one virus and DNA A of a second virus. We demonstrate that ACMV can mediate the systemic movement of ICMV, TGMV and AbMV DNA A components. In reciprocal experiments, neither TGMV nor AbMV can mediate the systemic movement of ACMV DNA A although they can support the movement of each other's DNA A. The variation in movement protein specificity suggests evolutionary divergence of New and Old World geminiviruses. Co-inoculation of combinations of ACMV and ICMV genome components into discriminating hosts and comparison of their behavior in N. benthamiana and N. tabacum leaf disc assays suggests that the host range of ICMV, a subset of that of ACMV, is restricted by impaired viral DNA replication rather than the inability of the virus to spread in non-host backgrounds.