TIP, a novel host factor linking callose degradation with the cell-to-cell movement of Potato virus X.
The cell-to-cell movement of Potato virus X (PVX) requires four virus-encoded proteins, the triple gene block (TGB) proteins (TGB25K, TGB12K, and TGB8K) and the coat protein. TGB12K increases the plasmodesmal size exclusion limit (SEL) and may, therefore, interact directly with components of the cell wall or with plant proteins associated with bringing about this change. A yeast two-hybrid screen using TGB12K as bait identified three TGB12K-interacting proteins (TIP1, TIP2, and TIP3). All three TIPs interacted specifically with TGB12K but not with TGB25K or TGB8K. Similarly, all three TIPs interacted with beta-1,3-glucanase, the enzyme that may regulate plasmodesmal SEL through callose degradation. Sequence analyses revealed that the TIPs encode very similar proteins and that TIP1 corresponds to the tobacco ankyrin repeat-containing protein HBP1. A TIP1::GFP fusion protein localized to the cytoplasm. Coexpression of this fusion protein with TGB12K induced cellular changes manifested as deposits of additional cytoplasm at the cell periphery. This work reports a direct link between a viral movement protein required to increase plasmodesmal SEL and a host factor that has been implicated as a key regulator of plasmodesmal SEL. We propose that the TIPs are susceptibility factors that modulate the plasmodesmal SEL.
Fridborg
Ingela
I
Department of Disease and Stress Biology, John Innes Centre, Norwich NR4 7UH, UK.
Grainger
Jef
J
Page
Anthony
A
Coleman
Mark
M
Findlay
Kim
K
Angell
Susan
S
D000595:Amino Acid Sequence; D017089:Ankyrin Repeat / Q000235:genetics / Q000502:physiology; D001692:Biological Transport; D043326:Glucan 1,3-beta-Glucosidase; D005936:Glucans / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D018515:Plant Leaves / Q000235:genetics / Q000648:ultrastructure / Q000821:virology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D017863:Potexvirus / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D025941:Protein Interaction Mapping; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D020798:Two-Hybrid System Techniques; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism; D001617:beta-Glucosidase / Q000378:metabolism
D005936:Glucans; D008164:Luminescent Proteins; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; D049452:Green Fluorescent Proteins; C048306:callose; D001617:beta-Glucosidase; D043326:Glucan 1,3-beta-Glucosidase