Diversity and interactions of begomoviruses and their associated DNA-satellites

To study the diversity of begomovirus/DNA-satellite complexes, plants of one crop species (okra; Abelmoschus esculentus) and one weed species (Ageratum conyzoides), both with leaf curling symptoms, were analyzed. Sequence analyses of complete genome components revealed a unique begomovirus/DNA-satellite complex in both plants. Okra was found to harbor infection with viruses of three begomovirus species, including the new recombinant species Okra leaf curl Cameroon virus, as well as one betasatellite and two divergent alphasatellites. The analysis of A. conyzoides revealed infection with a previously un-described complex of a begomovirus, betasatellite and alphasatellite. The results suggest that the diversity of begomoviruses and their associated DNA-satellites in Africa is much higher than previously thought, and that it may be similar to the diversity in Asia. Begomoviruses and satellites from different geographic regions, such as Africa and Asia, are genetically different. To test the compatibility of begomoviruses and satellites from Asia, Africa and the Mediterranean Region, inoculation experiments were carried out in the model host Nicotiana benthamiana using agroinfectious constructs for different begomoviruses and satellites. It was found that the tested begomoviruses and satellites could functionally interact with non-cognate betasatellites and alphasatellites with varying efficiencies. The results showed that the functional requirements for interaction between begomovirus and satellite can be quite relaxed. Thus, it is quite possible that new begomovirus-satellite combinations with components from different geographic regions will be formed, which may overcome plant resistance and increase the host range of begomoviruses. Functional studies were carried out on the betasatellite-associated monopartite begomovirus Cotton leaf curl Kokhran virus. Mutation analyses of the coat protein (CP), V2, C2 and C4 genes showed that CP, V2 and C2 are pathogenicity determinants and that they are involved in facilitating virus movement and maintenance of betasatellites. C4 is responsible for symptom induction, but it was not specifically required to maintain betasatellites.