Secoviridae: A Family of Plant Picorna‐Like Viruses with Monopartite or Bipartite Genomes

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Abstract Members of the family Secoviridae , referred to as secovirids, are plant viruses that share features with animal and human viruses of the family Picornaviridae and other insect or marine viruses of the order Picornavirales . These common features include a conserved structure of the icosahedral virus particles, the expression of viral proteins by proteolytic cleavage of large polyproteins and viral replication proteins with conserved sequence motifs, including the viral RNA‐dependent RNA polymerase and protease. Secovirids also share the distinguishing feature of encoding specialised proteins that enable their movement in plant and counteract plant defence mechanisms, such as RNA silencing. The family Secoviridae includes eight genera. Members of the genera Comovirus , Fabavirus , Nepovirus , Cheravirus , Sadwavirus and Torradovirus have a bipartite positive‐strand RNA genome, whereas members of the genera Sequivirus and Waikavirus have a monopartite genome. Key Concepts Many plant viruses are related to animal and human viruses of the family Picornaviridae and to other picorna‐like viruses infecting algae and arthropods. A recent update in the taxonomy of plant picorna‐like viruses has led to the creation of the family Secoviridae which amalgamates the previous families Comoviridae and Sequiviridae as well as the genera Cheravirus , Sequivirus and Torradovirus . Secovirids share common characteristics including having both similar virus particle structures and genomic organizations and requiring specialised proteins to facilitate their movement within the host plant or counteract plant defence mechanism. Secovirids produce their proteins in the form of large polyproteins that are cleaved at specific sites by a viral protease. Replication of the viral RNA occurs in large protein complexes in association with intracellular membranes from the host. Plant cells infected with secovirids generally display tubular structures that are composed of the viral movement protein, contain virus‐like particles and traverse the cell wall. These tubular structures are involved in the movement of the virus from cell to cell. Secovirids can be transmitted through seeds and pollen or with the help of nematode or arthropod vectors and their spread in the field is largely dependent on their mode of transmission. Some secovirids have been successfully exploited as plant vectors, allowing epitope presentation for vaccine production, expression of proteins in plants and silencing of endogenous plant genes.