Cell death triggering and effector recognition by Sw-5 SD-CNL proteins from resistant and susceptible tomato isolines to Tomato spotted wilt virus.
Only a limited number of dominant resistance genes acting against plant viruses have been cloned, and further functional studies of these have been almost entirely limited to the resistance genes Rx against Potato virus X (PVX) and N against Tobacco mosaic virus (TMV). Recently, the cell-to-cell movement protein (NSM) of Tomato spotted wilt virus (TSWV) has been identified as the avirulence determinant (Avr) of Sw-5b-mediated resistance, a dominant resistance gene which belongs to the class of SD-CC-NB-LRR (Solanaceae domain-coiled coil-nucleotide-binding-leucine-rich repeat, SD-CNL) resistance genes. On transient expression of the NSMprotein in tomato and transgenic Nicotiana benthamiana harbouring the Sw-5b gene, a hypersensitive cell death response (HR) is triggered. Here, it is shown that high accumulation of the Sw-5b protein in N. benthamiana leaves, achieved by co-expression of the Sw-5b protein with RNA silencing suppressors (RSSs), leads to auto-activity in the absence of NSM. In a similar approach, Sw-5a, the highest conserved paralogue of Sw-5b from Solanum peruvianum, also triggered HR by auto-activation, whereas the highest conserved orthologue from susceptible S. lycopersicum, named Sw-5aS, did not. However, neither of the last two homologues was able to trigger an NSM-dependent HR. Truncated and mutated versions of these Sw-5 proteins revealed that the NB-ARC [nucleotide-binding adaptor shared by Apaf-1 (from humans), R proteins and CED-4 (from nematodes)] domain is sufficient for the triggering of HR and seems to be suppressed by the SD-CC domain. Furthermore, a single mutation was sufficient to restore auto-activity within the NB-ARC domain of Sw-5aS. When the latter domain was fused to the Sw-5b LRR domain, NSM-dependent HR triggering was regained, but not in the presence of its own Sw-5aSLRR domain. Expression analysis in planta revealed a nucleocytoplasmic localization pattern of Sw-5b, in which the SD-CC domain seems to be required for nuclear translocation. Although the Sw-5 N-terminal CC domain, in contrast with Rx, contains an additional SD, most findings from this study support a conserved role of domains within NB-LRR (NLR) proteins against plant viruses.
Laboratory of Virology, Department of Plant Sciences, Wageningen University, Droevendaalsesteeg 1, Wageningen, PB, 6708, the Netherlands.|Department of Cell Biology, Institute of Biological Sciences, University of Brasília (UnB), Asa Norte 70910-900, Brasília, DF, Brazil.
Athos Silva
AS
De Oliveira
Laboratory of Virology, Department of Plant Sciences, Wageningen University, Droevendaalsesteeg 1, Wageningen, PB, 6708, the Netherlands.
Ivo
I
Koolhaas
Embrapa Vegetable Crops (CNPH), BR 060 Km 09, 70351-970, Brasília, DF, Brazil.
Leonardo Silva
LS
Boiteux
Department of Bioinformatics and Structural Biochemistry, Institute of Biochemistry of the Romanian Academy, Splaiul Independentei 296, Bucharest, 060036, Romania.
Octav F
OF
Caldararu
Department of Bioinformatics and Structural Biochemistry, Institute of Biochemistry of the Romanian Academy, Splaiul Independentei 296, Bucharest, 060036, Romania.
Andrei-Jose
AJ
Petrescu
Department of Cell Biology, Institute of Biological Sciences, University of Brasília (UnB), Asa Norte 70910-900, Brasília, DF, Brazil.
Renato
R
Oliveira Resende
Laboratory of Virology, Department of Plant Sciences, Wageningen University, Droevendaalsesteeg 1, Wageningen, PB, 6708, the Netherlands.
Richard
0000-0001-7360-1884
R
Kormelink
D000595:Amino Acid Sequence; D000596:Amino Acids; D016923:Cell Death; D002467:Cell Nucleus / Q000378:metabolism; D060467:Disease Resistance; D004198:Disease Susceptibility; D018506:Gene Expression Regulation, Plant; D018551:Solanum lycopersicum / Q000235:genetics / Q000821:virology*; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D010935:Plant Diseases / Q000821:virology*; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism*; D053830:Plant Viral Movement Proteins / Q000378:metabolism; D030821:Plants, Genetically Modified; D000072417:Protein Domains; D021381:Protein Transport; D013347:Subcellular Fractions / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics / Q000821:virology; D017865:Tospovirus / Q000502:physiology*
D000596:Amino Acids; D010940:Plant Proteins; D053830:Plant Viral Movement Proteins
NB-LRR; NSM; SD-CNL; Sw-5; Sw-5b; tomato; tospoviruses