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

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.

Identification of Cleavage Sites Recognized by the 3C-Like Cysteine Protease within the Two Polyproteins of Strawberry Mottle Virus

“…Strawberry mottle virus (SMoV) is one of the viruses found in association with this disease ( Martin and Tzanetakis, 2013 ). The species Strawberry mottle virus has been classified within the family Secoviridae (order Picornavirales ) but is currently not assigned to a specific genera, mostly because its genomic organization has not yet been clarified ( Sanfacon et al, 2011 ; Sanfacon, 2015 ). Similar to the majority of members of the family Secoviridae (referred to as secovirids), the SMoV genome consists of two positive sense RNA molecules.…”

“…Similar to the majority of members of the family Secoviridae (referred to as secovirids), the SMoV genome consists of two positive sense RNA molecules. Each RNA encodes one large polyprotein referred to as P1 (∼215 kDa) and P2 (∼190 kDa) for RNA1 and RNA2, respectively ( Thompson et al, 2002 ; Sanfacon, 2015 ; Bhagwat et al, 2016 ). The two polyproteins are presumably cleaved by an RNA1-encoded 3C-like protease (related to the 3C proteases of picornaviruses) ( Gorbalenya et al, 1989 ) to release mature proteins and intermediate precursor proteins made up of two or more protein domains.…”

Comparison of Serological and Molecular Methods With High-Throughput Sequencing for the Detection and Quantification of Grapevine Fanleaf Virus in Vineyard Samples

“…While some viruses might not be directly linked to a particular disease, others are of great economic concern to the grapevine industry. The grapevine fanleaf virus (GFLV) from the genus Nepovirus in the family Secoviridae ( Sanfaçon, 2015 ) causes fanleaf degeneration disease ( Schmitt-Keichinger et al, 2017 ). This disease is of major economic concern ( Andret-Link et al, 2004 ).…”

RNA2‐encoded VP37 protein ofBroad bean wilt virus 1is a determinant of pathogenicity, host susceptibility, and a suppressor of post‐transcriptional gene silencing

“…Broad bean wilt virus 1 (BBWV‐1) is the member type of the genus Fabavirus in the family Secoviridae , which contains 81 virus species (Thompson et al ., 2017). Members of the family Secoviridae have monopartite or bipartite single‐stranded RNA genomes of positive polarity (ssRNA+) encoding polyproteins further processed into functional polypeptides (Sanfaçon, 2015). The genus Fabavirus contains seven viral species: Broad bean wilt virus 1 (BBWV‐1), Broad bean wilt virus 2 (BBWV‐2), Cucurbit mild mosaic virus (CMMV), Gentian mosaic virus (GeMV), Lamium mild mosaic virus (LMMV), Grapevine fabavirus (GFabV), and Prunus virus F (PrVF) (Kobayashi et al ., 2003; Kobayashi et al ., 2005; Dong et al ., 2012; Rangel et al ., 2013; Al Rwahnih et al ., 2016; Villamor et al ., 2017).…”

“…(King et al ., 2011; Ferriol et al ., 2013). BBWV‐1 has a bipartite genome (RNA1 and RNA2) that is encapsidated into virions with icosahedral morphology (Sanfaçon, 2015). RNA1 (c.5.8 kb) contains an open reading frame (ORF) encoding a polyprotein that renders, after proteolytic cleavage, a protease cofactor (PRO‐CO), a helicase (HEL), a viral genome‐linked protein (VPg), a protease (PRO), and an RNA‐dependent RNA polymerase (POL).…”