Endogenous pararetroviruses--a reservoir of virus infection in plants

Endogenous pararetrovirus sequences (EPRV) belonging to the plant virus family Caulimoviridae have been discovered in the genomes of a wide range of Angiosperms. Although knowledge of EPRVs in plants is still in its infancy, it has been shown clearly in three different plant-virus pathosystems that these integrations are capable of generating functional circular viral genomes, and can thus trigger systemic infection. Here, we recapitulate information gathered over the last 15 years on how EPRVs contribute to virus replication in plants. We first present recent advances in our understanding of the molecular mechanisms involved in the transition from integrated to circular viral forms before addressing how EPRVs are controlled in planta.