title: The role of the Cucumber mosaic virus 2b protein in viral movement and symptom induction.
abstract: The Cucumber mosaic virus (CMV) 2b protein is a counter-defense factor and symptom determinant. Conserved domains in the 2b protein sequence were mutated in the 2b gene of strain Fny-CMV. The effects of these mutations were assessed by infection of Nicotiana tabacum, N. benthamiana, and Arabidopsis thaliana (ecotype Col-0) with mutant viruses and by expression of mutant 2b transgenes in A. thaliana. We confirmed that two nuclear localization signals were required for symptom induction and found that the N-terminal domain was essential for symptom induction. The C-terminal domain and two serine residues within a putative phosphorylation domain modulated symptom severity. Further infection studies were conducted using Fny-CMVdelta2b, a mutant that cannot express the 2b protein and that induces no symptoms in N. tabacum, N. benthamiana, or A. thaliana ecotype Col-0. Surprisingly, in plants of A. thaliana ecotype C24, Fny-CMVdelta2b induced severe symptoms similar to those induced by the wild-type virus. However, C24 plants infected with the mutant virus recovered from disease while those infected with the wild-type virus did not. Expression of 2b transgenes from either Fny-CMV or from LS-CMV (a mild strain) in Col-0 plants enhanced systemic movement of Fny-CMVdelta2b and permitted symptom induction by Fny-CMVdelta2b. Taken together, the results indicate that the 2b protein itself is an important symptom determinant in certain hosts. However, they also suggest that the protein may somehow synergize symptom induction by other CMV-encoded factors.
authors.affiliation: Department of Plant Sciences, University of Cambridge, Cambridge, CB2 3EA, UK.
authors.forename: Mathew
authors.initials: M
authors.lastname: Lewsey
authors.forename: Monique
authors.initials: M
authors.lastname: Surette
authors.forename: Fiona C
authors.initials: FC
authors.lastname: Robertson
authors.forename: Heiko
authors.initials: H
authors.lastname: Ziebell
authors.forename: Sun Hee
authors.initials: SH
authors.lastname: Choi
authors.forename: Ki Hyun
authors.initials: KH
authors.lastname: Ryu
authors.forename: Tomas
authors.initials: T
authors.lastname: Canto
authors.forename: Peter
authors.initials: P
authors.lastname: Palukaitis
authors.forename: Tina
authors.initials: T
authors.lastname: Payne
authors.forename: John A
authors.initials: JA
authors.lastname: Walsh
authors.forename: John P
authors.initials: JP
authors.lastname: Carr
mesh_terms: D017360:Arabidopsis / Q000821:virology; D017799:Cucumovirus / Q000235:genetics / Q000472:pathogenicity*; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010935:Plant Diseases / Q000821:virology*; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary / Q000502:physiology; D014026:Nicotiana / Q000821:virology; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
chemical_list: C404227:2b protein, cucumber mosaic virus; D021382:Protein Sorting Signals; D014764:Viral Proteins