r genes: structure, recognition, signaling, & evolution – part 1 major classes of r genes r...
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R genes: Structure, recognition, signaling, & evolution – part 1
• Major classes of R genes
• R gene structure
• Early signaling events
• R gene evolution
The zigzag model for plant pathogen interactions
Dangl and Jones. 2006. Nature 444:323-329
Plant immune system
Dangl. 2013. Science. 341:746
R protein structure
R proteins encompass multiple domains involved in different aspects of activation and signaling, and intramolecular interaction is involved.
DomainsTIR – Toll/Interleukin-1 receptorCC – Coiled coilNBS – Nucleotide binding siteLRR – Leucine-rich repeat
R protein classesTIR-NBS-LRR, TNLCC-NBS-LRR, CNL
NB-LRR, NBS-LRR, NLR – Nucleotide-binding leucine-rich repeat
Liu et al. 2007. J. Genet. Genom. 34:765-776
Cloned disease resistance genes
NBS-LRR is largest class
Major subclasses of NBS-LRR are: - CC-NBS-LRR - TIR-NBS-LRR
R gene class and pathogen are notcorrelated
TIR-NBS-LRR are not found incereals
Liu et al. 2007. J. Genet. Genom. 34:765-776
Major classes of R proteins
Tammeling et al. (2002) Plant Cell 14, 2929–2939
I-2
Mi-1
Nucleotide binding site (NBS)
P loop sequences
kinase 2 4 hydrophobic amino acids followed by D (e.g. LIVLD )
kinase 3a Highly conserved tyrosine or arginine (e.g. FGNGSR)
GLPL
MHDV
Inferred structure of R protein nucleotide binding sites
McHale et al. 2006.Genome Biology.7:212
Inferred structure of LRR domain
McHale et al. 2006.Genome Biology.7:212
Variation in numbers of LRRs
Structural models of domains in NLR proteins
Takken. 2012. Curr. Opin. Plant Biol. 15:375-384
Model of LRR motif of lettuce downy mildew resistance protein, Dm3
Michelmore. 2013. Annu. Rev. Phytopathol. 51:291-319
Michelmore and Meyers. 1998. Genome Res. 8: 1113-1130
LRR is least conserved part of R genes
NLR proteins are involved in plant & animal innate immunity
Bonardi et al. (2012) Curr. Opin. Immunol. 24:41-50
Evidence for intramolecular interaction between domains of a CNL protein
Moffett et al. (2002) EMBO J. 21:4511
CP-independent HR when TEX’d
Co-expression of full-length GPA2 with either LRR or ARC−LRR of Rx did not lead to a CP-dependent HR. However, co-expression of GPA2 with Rx NBS−LRR resulted in a CP-dependent HR (Figure 2B). This result demonstrates that a CC domain can be provided by full-length CC−NBS−LRR protein. Our observation that Rx NBS−LRR produced a CP-dependent HR when expressed in rx genotype potato leaves can be explained in the same way (Figure 2C). Presumably, a CC domain was provided to NBS−LRR by full-length homologues of Rx and GPA2 that are present in the rx potato genome (Bendahmane et al., 1999).
Intramolecular interactions - continued
Mestre. 2006. Plant Cell. 18:491-501
N protein oligomerizes in response to elicitor
NLR proteins – Mechanisms for activation
Bonardi et al. (2012) Curr. Opin. Immunol. 24:41-50
NLR folding and signaling
Takken. 2012. Curr. Opin. Plant Biol. 15:375-384
Ting et al. 2008. Nat. Rev. Immunol. 8:372-379
Signaling by animal NLR proteins