[Geminivirus replication: rolling circle mechanism in plants]

Geminiviruses are single-stranded DNA viruses that infect most plants worldwide. They replicate through a rolling circle mechanism which allows the production of a large amount of single-stranded viral DNA. This mechanism has been studied in detail for prokaryotic replicons but has also been described for eukaryotic replicons. The viral Rep protein is the key element in this process and combines three functions essential for replication: recognition of the viral origin of replication, cleavage of the origin and production of the primer necessary to replicate the viral DNA, and a replicative helicase activity. Furthermore by associating with several host proteins Rep interferes with the cell cycle control to produce a favourable environment for the replication of the virus. Recent advances have been reported concerning the demonstration of the helicase activity of Rep protein and the tertiary structure of its N-terminal domain; our review will focus on these two aspects in relation with the rolling circle replication mechanism.