title: Tobacco mosaic virus movement protein enhances the spread of RNA silencing.
abstract: Eukaryotic cells restrain the activity of foreign genetic elements, including viruses, through RNA silencing. Although viruses encode suppressors of silencing to support their propagation, viruses may also exploit silencing to regulate host gene expression or to control the level of their accumulation and thus to reduce damage to the host. RNA silencing in plants propagates from cell to cell and systemically via a sequence-specific signal. Since the signal spreads between cells through plasmodesmata like the viruses themselves, virus-encoded plasmodesmata-manipulating movement proteins (MP) may have a central role in compatible virus:host interactions by suppressing or enhancing the spread of the signal. Here, we have addressed the propagation of GFP silencing in the presence and absence of MP and MP mutants. We show that the protein enhances the spread of silencing. Small RNA analysis indicates that MP does not enhance the silencing pathway but rather enhances the transport of the signal through plasmodesmata. The ability to enhance the spread of silencing is maintained by certain MP mutants that can move between cells but which have defects in subcellular localization and do not support the spread of viral RNA. Using MP expressing and non-expressing virus mutants with a disabled silencing suppressing function, we provide evidence indicating that viral MP contributes to anti-viral silencing during infection. Our results suggest a role of MP in controlling virus propagation in the infected host by supporting the spread of silencing signal. This activity of MP involves only a subset of its properties implicated in the spread of viral RNA.
authors.affiliation: Department of Plant Physiology, Botanical Institute, University of Basel, Basel, Switzerland.
authors.forename: Hannes
authors.initials: H
authors.lastname: Vogler
authors.forename: Myoung-Ok
authors.initials: MO
authors.lastname: Kwon
authors.forename: Vy
authors.initials: V
authors.lastname: Dang
authors.forename: Adrian
authors.initials: A
authors.lastname: Sambade
authors.forename: Monika
authors.initials: M
authors.lastname: Fasler
authors.forename: Jamie
authors.initials: J
authors.lastname: Ashby
authors.forename: Manfred
authors.initials: M
authors.lastname: Heinlein
mesh_terms: D015967:Gene Expression Regulation, Viral; D054884:Host-Pathogen Interactions; D053830:Plant Viral Movement Proteins / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified; D034622:RNA Interference; D018749:RNA, Plant / Q000235:genetics; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism / Q000821:virology*; D014027:Tobacco Mosaic Virus / Q000235:genetics* / Q000378:metabolism
chemical_list: D053830:Plant Viral Movement Proteins; D018749:RNA, Plant