DNA replication and Pathogenecity of MYMIV

Abstract

Geminiviridae is a large family of single stranded DNA plant viruses, transmitted by white fly Bamesia tabacci, and they are the major causes of huge agro-economical losses worldwide. Mungbean yellow mosaic India virus (MYMIV) belongs to the genus begomovirus, the predominant variety of geminiviruses in northern part of Indian subcontinent. It has bipartite genome, which replicates via rolling circle (RCR) model with the help of few viral and several host factors. We have focused our efforts to understand the mechanism of initiation and immediate post-initiation phases of viral RCR. The Rep-protein encoded by the virus binds to the iterons present in the origin of replication, melts the origin, and subsequently nicks a conserved specific sequence of DNA, the region from where the RCR begins. The Rep protein also carries out the displacement of the parental strand required for the passage of replication fork. We have identified few host factors that act as accessory proteins of Rep during these phases of replication as mentioned. The high phyto-pathogenicity of the virus may be attributed to its potential to suppress host antiviral response, i.e., RNA silencing. We have developed various assays to identify viral RNAi suppressors. The AC2 suppressor protein of the MYMIV has been characterized for its various activities and its suppression domain has been mapped. This review will primarily focus upon the understanding the mechanistic aspect of initiation of MYMIV replication, the biochemical activity of the replication in relation to host as well as viral factors; and the RNA silencing suppressor activity of the virus protein AC2 and its potential applications.