Begomovirus DNA replication and pathogenicity

Begomoviridae is the largest genus of the family of single stranded DNA plant viruses, Geminiviridae and is responsible for significant agro-economic losses worldwide. Its small single-stranded DNA genome primarily replicates by rolling circle replication (RCR) mode with the help of certain viral and host factors. The role of virus encoded Rep protein in initiation and immediate post-initiation phases of RCR has been the subject of various studies. We have identified many host proteins which interact with Rep protein of a member of Begomovirus, namely, Mungbean yellow mosaic India virus, thereby playing a role in viral DNA replication. Of these, the role of host RAD54 protein is significant as the rad54 mutant of Arabidopsis does not permit mini viral DNA replication. The plant hosts protect themselves from begomoviruses by activating RNA interference (RNAi) pathways targeted against the viruses. However, the virus can also sometime overcome this form of host defence by encoding RNA silencing suppressors, which attenuate host RNAi and are regarded as major pathogenicity determinants. The viral suppressors do not share any signature sequences and are structurally and mechanistically dissimilar. These can be detected effectively, only through specialized functional assays. In this review, we also point out the potential biotechnological applications of the suppressors and discuss about various possible containment strategies for begomoviruses, including an exciting new approach involving artificial micro- RNAs