title: Alfalfa dwarf cytorhabdovirus P protein is a local and systemic RNA silencing supressor which inhibits programmed RISC activity and prevents transitive amplification of RNA silencing.
abstract: Plants employ RNA silencing as an innate defense mechanism against viruses. As a counter-defense, plant viruses have evolved to express RNA silencing suppressor proteins (RSS), which target one or more steps of the silencing pathway. In this study, we show that the phosphoprotein (P) encoded by the negative-sense RNA virus alfalfa dwarf virus (ADV), a species of the genus Cytorhabdovirus, family Rhabdoviridae, is a suppressor of RNA silencing. ADV P has a relatively weak local RSS activity, and does not prevent siRNA accumulation. On the other hand, ADV P strongly suppresses systemic RNA silencing, but does not interfere with the short-distance spread of silencing, which is consistent with its lack of inhibition of siRNA accumulation. The mechanism of suppression appears to involve ADV P binding to RNA-induced silencing complex proteins AGO1 and AGO4 as shown in protein-protein interaction assays when ectopically expressed. In planta, we demonstrate that ADV P likely functions by inhibiting miRNA-guided AGO1 cleavage and prevents transitive amplification by repressing the production of secondary siRNAs. As recently described for lettuce necrotic yellows cytorhabdovirus P, but in contrast to other viral RSS known to disrupt AGO activity, ADV P sequence does not contain any recognizable GW/WG or F-box motifs, which suggests that cytorhabdovirus P proteins may use alternative motifs to bind to AGO proteins.
authors.affiliation: Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, St. Lucia, QLD 4072, Australia. Electronic address: nicobejerman@gmail.com.
authors.forename: Nicolás
authors.initials: N
authors.lastname: Bejerman
authors.affiliation: Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, St. Lucia, QLD 4072, Australia. Electronic address: krinpreet.mann@canada.ca.
authors.forename: Krin S
authors.initials: KS
authors.lastname: Mann
authors.affiliation: Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, St. Lucia, QLD 4072, Australia. Electronic address: r.dietzgen@uq.edu.au.
authors.forename: Ralf G
authors.initials: RG
authors.lastname: Dietzgen
mesh_terms: D000818:Animals; D060565:Argonaute Proteins / Q000235:genetics / Q000378:metabolism; D044782:F-Box Motifs / Q000235:genetics; D035683:MicroRNAs / Q000819:agonists / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D010935:Plant Diseases / Q000821:virology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D010942:Plant Viruses / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000819:agonists / Q000378:metabolism; D012367:RNA, Viral / Q000378:metabolism; D034743:RNA-Induced Silencing Complex / Q000235:genetics / Q000378:metabolism*; D012209:Rhabdoviridae / Q000235:genetics / Q000378:metabolism*; D014026:Nicotiana / Q000235:genetics / Q000821:virology; D015678:Viral Structural Proteins / Q000378:metabolism*
chemical_list: D060565:Argonaute Proteins; D035683:MicroRNAs; D010750:Phosphoproteins; D010940:Plant Proteins; D034741:RNA, Small Interfering; D012367:RNA, Viral; D034743:RNA-Induced Silencing Complex; D015678:Viral Structural Proteins
keywords: Alfalfa dwarf cytorhabdovirus; Argonaute proteins; Phosphoprotein; Protein-protein interactions; RNA silencing suppression; Transitivity