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