1. Induced Systemic Resistance
(ISR)
Plant responses to plant growth promoting rhizobacteria
Herbivore induced resistance

2. Biologically induced systemic resistance
Pieterse et al. (2014) Annu. Rev. Phytopathol. 52:347-75

3. Conrath. 2011. Trends Plant Sci. 16:524-531

4. Root colonization by beneficial soil bacteria
Pieterse et al. (2014) Annu. Rev. Phytopathol. 52:347-75

5. Plant growth-promoting effects of P. fluorescens WCS417r
Pieterse et al. (2014) Annu. Rev. Phytopathol. 52:347-75

6. Systemic protection against Cucumber mosaic virus
Nonbacterized
Bacillus pumulis strain SE34
Kloepper Phytopathology. 94:

7. P. fluorescens WCS417r and iron deficiency induce MYB72
Pieterse et al. (2014) Annu. Rev. Phytopathol. 52:347-75

8. Properties of PGPR Stimulate growth N fixation
Increase solubility of limiting nutrients (siderophores)
Stimulate nutrient delivery and uptake
Production of phytohormones
Modulation of plant development (e.g. reduce ethylene enhances root growth)
Plant-mediated disease suppression
Non-pathogens antagonize pathogens (competition, antibiotics, lytic enzymes)
Activating plant to better defend itself (ISR)
Induced resistance observed on spatially separated parts of same plant

9. The nature of systemically induced resistance in plants
(A) Characteristics of induced systemic resistance
The defensive capacity of the plant is enhanced through microbial stimulation or similar stresses
The enhanced defensive capacity is expressed systemically throughout the plant
Induced systemic resistance is active against fungi, bacteria, viruses and, sometimes, nematodes and insects
Once induced, systemic resistance is maintained for prolonged periods
(B) Mechanisms of induced systemic resistance
Developmental, escape: linked to growth promotion
Physiological, tolerance: reduced symptom expression
Environmental: associated with microbial antagonism in the rhizosphere; altered plant-insect interactions
Biochemical, resistance: induction of cell wall reinforcement,
Induction of phytoalexins
Induction of pathogenesis-related proteins
‘Priming’ of defence responses (resistance)
From Van Loon (2007) Eur. J. Plant Pathol. 119:

10. ISR potentiates plant defense responses
Fusarium wilt of carnation and radish
Biocontrol by P. fluorescens WCS358
Iron competition important: sid- mutant not effective
Biocontrol by P. fluorescens WCS417
Twice as effective
Sid-mutant still 100% effective
Worked when WCS417 and fusarium were spatially separated on the plant*
WCS417 did not trigger phytoalexin accumulation*
WCS417 treated plants produced more phytoalexin in response to Fusarium*
Root rot in bean
Accelerated and potentiated papilla formation
*Van Peer et al (1991) Phytopathol 81:

11. Plant-mediated*, broad-spectrum resistance response that is activated by selected strains of saprophytic rhizosphere bacteria. Many are PGPR. PGPR colonization non-specific; ability to induce SR has some specificity. * Inducing bacteria and pathogen can be spatially isolated

13. Summary of ISR molecular properties
ISR potentiates plant defense responses
ISR is SA-independent
ISR is independent of PR gene activation
ISR requires JA and C2H4 response pathways
ISR not associated with JA- and C2H4-responsive gene activation
ISR primes plant for enhanced C2H4 production?
Summary: compare and contrast ISR and SAR
Not covered in class:
1) bacterial determinants of ISR
2) field application of ISR

14. Changes in gene expression in bacterized plants
From Van Loon (2007) Eur. J. Plant Pathol. 119:

15. Specificity in ISR induction by Pseudomonas spp. strains
Root colonization is similar in all cases
From Van Loon (2007) Eur. J. Plant Pathol. 119:

16. Model system – Arabidopsis/Pseudomonas fluorescens WCS417r
For Ps
Control
WCS417r

17. Pieterse et al. (1996) Plant Cell 8, 1225-1237–
ISR is SA-independent W
Fusarium – W
P. syringae
Pieterse et al. (1996) Plant Cell 8,

18. Pieterse et al. (1996) Plant Cell 8, 1225-1237
ISR is independent of PR gene activation
R = root treatment; L = leaf treatment
Pieterse et al. (1996) Plant Cell 8,
*just prior to challenge inoc

19. ISR requires JA and C2H4 response pathways
Pieterse et al. (1998) Plant Cell 10,

20. ISR requires JA and C2H4 response pathways in that order
Figure 2C clearly shows that MeJA-mediated protection against P. s. tomato requires an intact response to ethylene, whereas ACC is fully active in jar1 plants.
Pieterse et al. (1998) Plant Cell 10,

21. Pieterse et al. (1998) Plant Cell 10, 1571-158

22. ISR not associated with JA- and C2H4-responsive gene activation
But expression of this (and not others) is potentiated in plants undergoing ISR
Van Wees et al. (1999) Plant Mol Biol 41:
So ISR is associated with potentiation of a specific set of JA-responsive genes?
Also, increased sensitivity rather than increased production of JA and C2H4
(see also Pieterse et al Physiol. Mol. Plant Pathol. 57: )
Pieterse et al. (1998) Plant Cell 10,

23. ISR primes plant for enhanced C2H4 production?
ISR plants do not show increased levels of C2H4, or JA,
but
ISR activated plants convert more ACC to C2H4

24. MYC2 transcription factor involved in priming induced systemic resistance
Pozo New Phytol. 180:

25. Herbivore induce resistance
Differential JA responses in Col-0 and jin1 plants in local and systemic leaves
Vos Front. Plant Sci. 4:539

26. Production of JA, JA-Ile, OPDA, and ABA in local and systemic Col-0 leaves
Vos Front. Plant Sci. 4:539

27. Effects of P. rapae and ABA on MYC and VSP1 expression
Vos Front. Plant Sci. 4:539

28. Effect of herbivory on P
Effect of herbivory on P. rapae performance in Col-0, aba2-1, and coi1-1 plants
Vos Front. Plant Sci. 4:539

29. Model for herbivore induced resistance in Arabidopsis
Vos Front. Plant Sci. 4:539

30. Comparison of SAR, HIR, and ISR mechanisms
Pieterse et al. (2014) Annu. Rev. Phytopathol. 52:347-75

31. 1) why is it important to study ISR?
Discussion
1) why is it important to study ISR?
2) do differences between ISR, HIR, SAR matter?
3) selective advantage to the plant and practical significance?
4) what role does root microbiome play in immunity
5) how might ISR be triggered?
Post translational mods ready to go
Enhanced sensitivity or ability to produce?