title: Cucumber mosaic virus 2b protein subcellular targets and interactions: their significance to RNA silencing suppressor activity.
abstract: The RNA silencing suppressor activity of the 2b protein of Cucumber mosaic virus (CMV) has been variously attributed to its nuclear targeting, its interaction with and inhibition of Argonaute 1 (AGO1), or its ability to bind small RNAs in vitro. In addition, the 2b ortholog of Tomato aspermy virus forms aggregates and binds RNAs in vitro. We have further studied the relationships between CMV 2b protein silencing suppressor activity and its subcellular distribution, protein-protein interactions in vivo, and interactions with small interfering RNAs in vitro. To do this, we tagged the protein with fluorescent markers and showed that it retained suppressor activity. We showed that the 2b protein is present in the nucleolus and that it self-interacts and interacts with AGO1 and AGO4 in vivo. Using a battery of mutants, we showed that the putative nuclear localization signals and phosphorylation motif of the 2b protein are not required for self-interaction or for interaction with AGO proteins. The occurrence of neither of these interactions or of nucleolar targeting was sufficient to provide local silencing-suppression activity. In contrast, the ability of the 2b protein to bind small RNAs appears to be indispensable for silencing suppressor function.
authors.affiliation: Centro de Investigaciones Biológicas, CIB, CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain.
authors.forename: Inmaculada
authors.initials: I
authors.lastname: González
authors.forename: Llucia
authors.initials: L
authors.lastname: Martínez
authors.forename: Daria V
authors.initials: DV
authors.lastname: Rakitina
authors.forename: Mathew G
authors.initials: MG
authors.lastname: Lewsey
authors.forename: Félix A
authors.initials: FA
authors.lastname: Atencio
authors.forename: César
authors.initials: C
authors.lastname: Llave
authors.forename: Natalia O
authors.initials: NO
authors.lastname: Kalinina
authors.forename: John P
authors.initials: JP
authors.lastname: Carr
authors.forename: Peter
authors.initials: P
authors.lastname: Palukaitis
authors.forename: Tomás
authors.initials: T
authors.lastname: Canto
mesh_terms: D017799:Cucumovirus / Q000235:genetics / Q000378:metabolism*; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D019913:Nuclear Localization Signals / Q000235:genetics; D010766:Phosphorylation; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism / Q000821:virology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism / Q000821:virology; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C404227:2b protein, cucumber mosaic virus; D008164:Luminescent Proteins; D019913:Nuclear Localization Signals; D010940:Plant Proteins; D034741:RNA, Small Interfering; D014764:Viral Proteins