title: Interaction of a plant virus-encoded protein with the major nucleolar protein fibrillarin is required for systemic virus infection.
abstract: The nucleolus and specific nucleolar proteins are involved in the life cycles of some plant and animal viruses, but the functions of these proteins and of nucleolar trafficking in virus infections are largely unknown. The ORF3 protein of the plant virus, groundnut rosette virus (an umbravirus), has been shown to cycle through the nucleus, passing through Cajal bodies to the nucleolus and then exiting back into the cytoplasm. This journey is absolutely required for the formation of viral ribonucleoprotein particles (RNPs) that, themselves, are essential for the spread of the virus to noninoculated leaves of the shoot tip. Here, we show that these processes rely on the interaction of the ORF3 protein with fibrillarin, a major nucleolar protein. Silencing of the fibrillarin gene prevents long-distance movement of groundnut rosette virus but does not affect viral replication or cell-to-cell movement. Repressing fibrillarin production also localizes the ORF3 protein to multiple Cajal body-like aggregates that fail to fuse with the nucleolus. Umbraviral ORF3 protein and fibrillarin interact in vitro and, when mixed with umbravirus RNA, form an RNP complex. This complex has a filamentous structure with some regular helical features, resembling the RNP complex formed in vivo during umbravirus infection. The filaments formed in vitro are infectious when inoculated to plants, and their infectivity is resistant to RNase. These results demonstrate previously undescribed functions for fibrillarin as an essential component of translocatable viral RNPs and may have implications for other plant and animal viruses that interact with the nucleolus.
authors.affiliation: Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, United Kingdom.
authors.forename: Sang Hyon
authors.initials: SH
authors.lastname: Kim
authors.forename: Stuart
authors.initials: S
authors.lastname: Macfarlane
authors.forename: Natalia O
authors.initials: NO
authors.lastname: Kalinina
authors.forename: Daria V
authors.initials: DV
authors.lastname: Rakitina
authors.forename: Eugene V
authors.initials: EV
authors.lastname: Ryabov
authors.forename: Trudi
authors.initials: T
authors.lastname: Gillespie
authors.forename: Sophie
authors.initials: S
authors.lastname: Haupt
authors.forename: John W S
authors.initials: JW
authors.lastname: Brown
authors.forename: Michael
authors.initials: M
authors.lastname: Taliansky
mesh_terms: D029681:Arabidopsis Proteins / Q000378:metabolism / Q000502:physiology; D002466:Cell Nucleolus / Q000821:virology; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism* / Q000502:physiology*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D053830:Plant Viral Movement Proteins; D010942:Plant Viruses / Q000737:chemistry / Q000472:pathogenicity*; D021381:Protein Transport; D012261:Ribonucleoproteins / Q000378:metabolism; D014764:Viral Proteins / Q000378:metabolism*; D014777:Virus Diseases / Q000209:etiology*
chemical_list: D029681:Arabidopsis Proteins; D002868:Chromosomal Proteins, Non-Histone; D009687:Nuclear Proteins; D053830:Plant Viral Movement Proteins; D012261:Ribonucleoproteins; D014764:Viral Proteins; C047458:fibrillarin