The role of the Cucumber mosaic virus 2b protein in viral movement and symptom induction.

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.

[1]  P. Palukaitis,et al.  The 2b protein and the C-terminus of the 2a protein of cucumber mosaic virus subgroup I strains both play a role in viral RNA accumulation and induction of symptoms. , 2008, Virology.

[2]  Chengqi Lin,et al.  Structural basis for RNA‐silencing suppression by Tomato aspermy virus protein 2b , 2008, EMBO reports.

[3]  Priyanka Singh,et al.  Behavior of RNAi suppressor protein 2b of Cucumber mosaic virus in planta in presence and absence of virus , 2008, Virus Genes.

[4]  K. Lehto,et al.  Phenotypes and functional effects caused by various viral RNA silencing suppressors in transgenic Nicotiana benthamiana and N. tabacum. , 2008, Molecular plant-microbe interactions : MPMI.

[5]  J. O. Berry,et al.  A cucumber mosaic virus mutant lacking the 2b counter-defence protein gene provides protection against wild-type strains. , 2007, The Journal of general virology.

[6]  Ji-Shuang Chen,et al.  2b ORFs encoded by subgroup IB strains of cucumber mosaic virus induce differential virulence on Nicotiana species. , 2007, The Journal of general virology.

[7]  J. Jovel,et al.  Recovery of Nicotiana benthamiana Plants from a Necrotic Response Induced by a Nepovirus Is Associated with RNA Silencing but Not with Reduced Virus Titer , 2007, Journal of Virology.

[8]  S. Ding,et al.  Suppression of Antiviral Silencing by Cucumber Mosaic Virus 2b Protein in Arabidopsis Is Associated with Drastically Reduced Accumulation of Three Classes of Viral Small Interfering RNAs[W][OA] , 2007, The Plant Cell Online.

[9]  Fiona C. Robertson,et al.  Selective targeting of miRNA-regulated plant development by a viral counter-silencing protein. , 2007, The Plant journal : for cell and molecular biology.

[10]  T. Tuschl,et al.  Cucumber mosaic virus-encoded 2b suppressor inhibits Arabidopsis Argonaute1 cleavage activity to counter plant defense. , 2006, Genes & development.

[11]  Jinsong Bao,et al.  Hierarchical Action and Inhibition of Plant Dicer-Like Proteins in Antiviral Defense , 2006, Science.

[12]  N. Chua,et al.  MicroRNA Directs mRNA Cleavage of the Transcription Factor NAC1 to Downregulate Auxin Signals for Arabidopsis Lateral Root Development , 2005, The Plant Cell Online.

[13]  P. Palukaitis,et al.  Functional analysis of the Cucumber mosaic virus 2b protein: pathogenicity and nuclear localization. , 2004, The Journal of general virology.

[14]  Sang Hyon Kim,et al.  Escape of a plant virus from amplicon-mediated RNA silencing is associated with biotic or abiotic stress. , 2004, The Plant journal : for cell and molecular biology.

[15]  Valerian V Dolja,et al.  Viral RNA silencing suppressors inhibit the microRNA pathway at an intermediate step. , 2004, Genes & development.

[16]  P. Palukaitis,et al.  Construction of full-length cDNA clones of cucumber mosaic virus RNAs 1, 2 and 3: Generation of infectious RNA transcripts , 1990, Molecular and General Genetics MGG.

[17]  P. Palukaitis,et al.  The 2b protein of cucumoviruses has a role in promoting the cell-to-cell movement of pseudorecombinant viruses. , 2003, Molecular plant-microbe interactions : MPMI.

[18]  Bu-Jun Shi,et al.  Differential virulence by strains of Cucumber mosaic virus is mediated by the 2b gene. , 2002, Molecular plant-microbe interactions : MPMI.

[19]  P. Palukaitis,et al.  Virulence and differential local and systemic spread of cucumber mosaic virus in tobacco are affected by the CMV 2b protein. , 2002, Molecular plant-microbe interactions : MPMI.

[20]  M. Mayo,et al.  Umbravirus gene expression helps potato leafroll virus to invade mesophyll tissues and to be transmitted mechanically between plants. , 2001, Virology.

[21]  S. Ding,et al.  The suppressor of transgene RNA silencing encoded by Cucumber mosaic virus interferes with salicylic acid-mediated virus resistance. , 2001, Molecular plant-microbe interactions : MPMI.

[22]  M. Roossinck.  Cucumber mosaic virus, a model for RNA virus evolution. , 2001, Molecular plant pathology.

[23]  Philippe Mourrain,et al.  Arabidopsis SGS2 and SGS3 Genes Are Required for Posttranscriptional Gene Silencing and Natural Virus Resistance , 2000, Cell.

[24]  A. Lucy,et al.  Suppression of post‐transcriptional gene silencing by a plant viral protein localized in the nucleus , 2000, The EMBO journal.

[25]  P. Palukaitis,et al.  Subcellular distribution analysis of the cucumber mosaic virus 2b protein. , 2000, The Journal of general virology.

[26]  K. Paek,et al.  Isolation of a putative tobacco host factor interacting with cucumber mosaic virus-encoded 2b protein by yeast two-hybrid screening. , 1999, Molecules and cells.

[27]  K. Hellwald,et al.  Rearrangements in the 5′ Nontranslated Region and Phylogenetic Analyses of Cucumber Mosaic Virus RNA 3 Indicate Radial Evolution of Three Subgroups , 1999, Journal of Virology.

[28]  A. Lucy,et al.  Strong host resistance targeted against a viral suppressor of the plant gene silencing defence mechanism , 1999, The EMBO journal.

[29]  S. Clough,et al.  Floral dip: a simplified method for Agrobacterium-mediated transformation of Arabidopsis thaliana. , 1998, The Plant journal : for cell and molecular biology.

[30]  D. Baulcombe,et al.  Retracted: Viral pathogenicity determinants are suppressors of transgene silencing in Nicotiana benthamiana , 1998, The EMBO journal.

[31]  J. O. Berry,et al.  Salicylic Acid Can Induce Resistance to Plant Virus Movement , 1998 .

[32]  R. Symons,et al.  A novel naturally occurring hybrid gene encoded by a plant RNA virus facilitates long distance virus movement. , 1995, The EMBO journal.

[33]  P. Palukaitis,et al.  Mapping local and systemic symptom determinants of cucumber mosaic cucumovirus in tobacco. , 1994, The Journal of general virology.

[34]  R. Symons,et al.  New overlapping gene encoded by the cucumber mosaic virus genome. , 1994, Virology.