Emerging satellites associated with begomoviruses: World scenario

Abstract

Begomoviruses are abundant and worldwide in occurrence that cause economically important diseases not only in a vast range of crop plants but also in many weed plants which serve as reservoir host plants. Begomoviruses are associated with satellite molecules called as betasatellite and alphasatellite with DNA genomes approximately half the size of begomovirus DNA genomes. These satellites are also emerging very fast and are found abundantly in a number of crop plants associated with begomoviruses. Betasatellites are reported from the Old World, till today no betasatellite is reported from the New World though alphasatellites are now being reported from the New World too. Alphasatellites were earlier reported to be associated with monopartite begomoviruses only, but now they are reported with bipartite begomoviruses as well. This indicates their continuous emergence due to increasing host range. Genes encoded by the betasatellites (βC1) play important roles in the induction of symptoms and in gene silencing as suppressor of transcriptional and posttranscriptional gene silencing. Alphasatellites as such do not have any role in pathogenicity of begomoviruses. Some alphasatellites can attenuate disease symptoms caused by begomovirus-betasatellite complexes in the early stages of infection.