Plasmodesmal targeting and intercellular movement of potato mop-top pomovirus is mediated by a membrane anchored tyrosine-based motif on the lumenal side of the endoplasmic reticulum and the C-terminal transmembrane domain in the TGB3 movement protein.
Live-cell fluorescence microscopy was used to investigate the third triple gene block protein (TGB3) of potato mop-top pomovirus and its role in assisted targeting of TGB2 to plasmodesmata (PD). Wild-type and mutant TGB3 proteins were expressed under the control of the 35S promoter or from a virus reporter clone. Assisted targeting of TGB2 to PD was optimal when the proteins were expressed from a bicistronic plasmid in the relative ratios expected in a virus infection, suggesting that excess TGB3 inhibited PD localisation. Contrary to the generally accepted view, bimolecular fluorescence complementation showed that the TGB3 N terminus is located in the cytosol. Mutational analysis to dissect TGB3 sub domain functions showed that PD targeting was mediated by a composite signal comprising an ER-lumenal tyrosine-based motif and the C-terminal transmembrane domain. Mutation of either of these domains also abolished cell-to-cell movement of the virus. The results are discussed in the context of TGB3 membrane topology.
Tilsner
J
J
Plant Pathology Programme, Scottish Crop Research Institute, Invergowrie, DD2 5DA, UK.
Cowan
G H
GH
Roberts
A G
AG
Chapman
S N
SN
Ziegler
A
A
Savenkov
E
E
Torrance
L
L
D003600:Cytosol / Q000737:chemistry; D004721:Endoplasmic Reticulum / Q000821:virology*; D008856:Microscopy, Fluorescence; D053830:Plant Viral Movement Proteins / Q000378:metabolism*; D010942:Plant Viruses / Q000472:pathogenicity*; D031425:Plasmodesmata / Q000737:chemistry; D011485:Protein Binding; D021381:Protein Transport; D012328:RNA Viruses / Q000472:pathogenicity*; D011198:Solanum tuberosum / Q000821:virology*
D053830:Plant Viral Movement Proteins