1. PAMP-triggered immunity (PTI)
Recognition of danger signals
Distinguish self or damaged self versus non-self – fundamental to any immune system
PAMP or MAMP – pathogen/microbe-associated molecular pattern
DAMP – damage-associated molecular pattern
PRR – Pattern recognition receptors (receptor-like proteins/kinases)
Membrane receptors
Ligand-receptor interaction
Initiate signal transduction cascade
Conserved features across plants, insects, vertebrates
Adapted pathogens use effectors to suppress
PTI often considered weaker than ETI, but is it really?

2. The zigzag model for plant pathogen interactions
Dangl and Jones Nature 444:

3. How to distinguish a PAMP from an effector??
PAMPS can be widely conserved or narrowly conserved
Invariant or highly constrained sequence
PAMP is essential for microbial fitness and survival
Effector specifically contributes to virulence by targeting host (defense) physiology
Lines are blurry
From the plant immunity point of view, the nature and intrinsic
function of the ligand is not relevant as long as it timely and accurately betrays the potential microbial invader to the plant surveillance system. As a result of continuous coevolution between plant and pathogen, a wealth of plant perception systems for microbe-derived molecules has been shaped that reliably fulfills roles in mediating the establishment of plant immunity
Thomma et al. (2011) Plant Cell 23:4-15

4. Dubery et al. 2012. in Self and Nonself. pp79-107

5. Structure of bacterial lipopolysaccharide and peptidoglycan
Erbs and Newman (2012) Mol. Plant Pathol. 13:95-104

6. Pattern recognition receptors (PRRs)
First layer of active defense, extracellular membrane receptors
PRRs perceive PAMPs by receptor-ligand interactions
Evolutionarily ancient and some widely occurring in plant kingdom
Interfamily transfer of PRRs more successful than R genes
R proteins in contrast are evolutionarily young, with many novel members
Lines are blurry, some interactions classified as Avr-R gene may be re-classified as PAMP-PRR
Thomma et al. (2011) Plant Cell 23:4-15

7. Recognition of bacteria by plant PRRs
Zipfel Trends Immunol. 35:

8. Recognition of fungi by plant PRRs
Zipfel Trends Immunol. 35:

9. LysM domain-containing receptors
Antolin-Llovera et al. (2012) Annu. Rev. Phytopathol. 50:

10. Damage-associated molecular patterns (DAMPs) in plants
Tanaka et al Front. Plant Sci. 5:446

11. Recognition of the infectious self by plant PRRs
Zipfel Trends Immunol. 35:

12. Dubery et al. 2012. in Self and Nonself. pp79-107

13. Dubery et al. 2012. in Self and Nonself. pp79-107

14. Immune receptor complexes
Bӧhm et al Curr. Opin. Plant Biol. 20:47-54

15. Ligand-induced rearrangements of the FLS2 receptor complex
Bӧhm et al Curr. Opin. Plant Biol. 20:47-54

16. Ligand-induced oligomerization of LysM domain immune receptor complexes
Bӧhm et al Curr. Opin. Plant Biol. 20:47-54

17. Negative regulation of PRR complexes
Macho and Zipfel Mol. Cell 54:

18. Inhibition of flg22 perception by P. syringae pv. tomato
Nurnberger and Kemmerling (2009)

19. Zigzag model incorporating co-evolution between Cladosporium fulvum and tomato
Ecp6 – LysM effector
- competes with CEBiP
- present in all C.f. isolates
- widely occurs in fungi (chitin scavenging important for virulence)
- some tomato genotypes develop HR to Ecp6
Thomma et al. (2011) Plant Cell 23:4-15

20. PAMP perception
in animals and plants
Nurnberger and Kemmerling (2009)

21. Comparison of plant and animal
perception of conserved
microbial signatures
Ronald and Beutler (2010) Science

22. Some outstanding remaining questions
Match more PAMPs to their PRRs
PRR specificity?
do plants activate congruent pathways to different microbes?
How does PTI restrict pathogen growth?
Links between PTI and cell death?
Where does specificity in signaling occur for different microbes?
Can PRRs be pyramided to give broad spectrum immunity?
What molecular events initiate distinct signaling branches?
How is PTI tightly controlled to avoid autoimmune disorders?
Molecular interconnection between ETI and PTI?
How is PTI connected to hormone pathways involved in growth and development?