Complementation of African cassava mosaic virus AC2 gene function in a mixed bipartite geminivirus infection

We have previously demonstrated that African cassava mosaic virus (ACMV) DNAs A and B efficiently complement the systemic spread of tomato golden mosaic virus (TGMV) DNA A when co-agroinoculated onto Nicotiana benthamiana. Here, we show that a mixture of an ACMV DNA A AC2 mutant and DNA B that is normally unable to systemically infect N. benthamiana can do so at low frequency when co-agroinoculated with TGMV DNA A. Analysis of viral DNA showed that the AC2 mutation was retained during infection. The mixture of genomic components was sap transmissible, indicating that systemic infectivity is not specifically attributable to the use of agroinoculation. In the presence of TGMV DNA A, ACMV coat protein as well as the DNA B gene products BV1 and BC1 were detected in systemically infected tissues. The results demonstrate that dysfunctional AC2 can be complemented in planta by its TGMV homologue AL2.