title: Phloem flow strongly influences the systemic spread of silencing in GFP Nicotiana benthamiana plants.
abstract: The term 'RNA silencing' describes a process that results in the specific degradation of an RNA target. In plants, silenced tissues can initiate the spreading of the process into non-silenced regions by a mobile signal that can be transmitted over long distances. In the present work, we made use of a modified grafting approach to elucidate the driving force behind long-distance transport of the silencing signal. We made reciprocal grafts of two GFP-transgenic Nicotiana benthamiana lines, the non-silenced line 16c (sensor) and the silenced line 6.4 (inducer). We show that the direction of systemic spread of silencing from inducer to sensor can be manipulated by altering sink/source relations in the plant. Using radioactive phosphate as a phloem tracer, we demonstrated that plants that transmitted silencing from silenced scion to non-silenced rootstock had developed a persisting phloem flow from scion to rootstock. These data provide experimental proof of what has been hypothesized so far, that the silencing signal travels via phloem from source to sink. We present here evidence that the appearance of systemic silencing is not an accidental stochastic process, but can be predicted on the basis of the direction of phloem flow.
authors.affiliation: Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology - Hellas, GR-71110 Heraklion/Crete, Greece. barthelemy.tournier.1@ulaval.ca
authors.forename: Barthélémy
authors.initials: B
authors.lastname: Tournier
authors.forename: Martin
authors.initials: M
authors.lastname: Tabler
authors.forename: Kriton
authors.initials: K
authors.lastname: Kalantidis
mesh_terms: D018506:Gene Expression Regulation, Plant; D049452:Green Fluorescent Proteins / Q000032:analysis* / Q000235:genetics; D018515:Plant Leaves / Q000033:anatomy & histology / Q000378:metabolism / Q000502:physiology; D018517:Plant Roots / Q000378:metabolism / Q000502:physiology; D030821:Plants, Genetically Modified / Q000033:anatomy & histology / Q000378:metabolism / Q000502:physiology; D034622:RNA Interference / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000032:analysis / Q000235:genetics; D015398:Signal Transduction; D014026:Nicotiana / Q000235:genetics* / Q000378:metabolism / Q000502:physiology
chemical_list: D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins