Pararetroviruses: Plant Infecting dsDNA Viruses

Plant pararetroviruses (PRVs; family Caulimovirida) are non-enveloped double-stranded DNA viruses having either isometric or bacilliform virion. According to the current taxonomy, the family Caulimoviridae consists of ten genera with two newly added genera Dioscovirus and Vaccinivirus. PRVs have a genome size between 7 and 9 kilobase pairs and differ mainly based on the number of open reading frames (ORFs; 1 to 8) in each genus. These ORFs encode many functional proteins that help the virus to survive within the host cell. They are transmitted by aphids, mealy bugs, or leafhoppers. These viruses have a wide geographical distribution and infect a broad range of monocotyledonous and dicotyledonous plant species, making their early detection and control a paramount requirement. The transcriptional unit (promoter) of the PRV genome has become an interesting “modular cassette” to the molecular biologist worldwide for fine-tuning of gene expression in plants. The present review highlights the current taxonomy, genome structure, transmission, and diagnosis of pararetroviruses and how the “modular cassette” would help the modern biotechnology-based translational research.