Induced Systemic Resistance(ISR)

- Plant responses to plant growth promoting rhizobacteria

- Herbivore induced resistance

Pieterse et al. (2014) Annu. Rev. Phytopathol. 52:347-75

Biologically induced systemic resistance

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

Root colonization by beneficial soil bacteria

Pieterse et al. (2014) Annu. Rev. Phytopathol. 52:347-75

Plant growth-promoting effects of P. fluorescens WCS417r

Pieterse et al. (2014) Annu. Rev. Phytopathol. 52:347-75

Systemic protection against Cucumber mosaic virus

Kloepper. 2004. Phytopathology. 94:1259-1266

Bacillus pumulis strain SE34Nonbacterized

P. fluorescens WCS417r and iron deficiency induce MYB72

Pieterse et al. (2014) Annu. Rev. Phytopathol. 52:347-75

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

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. 119:243-254

ISR potentiates plant defense responses

Fusarium wilt of carnation and radishBiocontrol 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*

*Van Peer et al (1991) Phytopathol 81:728-734

Root rot in beanAccelerated and potentiated papilla formation

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

• 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 ISR2) field application of ISR

Summary of ISR molecular properties

From Van Loon (2007) Eur. J. Plant Pathol. 119:243-254

Changes in gene expression in bacterized plants

Specificity in ISR induction by Pseudomonas spp. strains

From Van Loon (2007) Eur. J. Plant Pathol. 119:243-254

Root colonization is similar in all cases

Model system – Arabidopsis/Pseudomonas fluorescens WCS417r

For Ps

Control

WCS417r

ISR is SA-independent

Pieterse et al. (1996) Plant Cell 8, 1225-1237

Fusarium

P. syringae

–

W

–

W

ISR is independent of PR gene activation

Pieterse et al. (1996) Plant Cell 8, 1225-1237 *just prior to challenge inoc

ISR requires JA and C2H4 response pathways

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

ISR requires JA and C2H4 response pathwaysin that order

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

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

ISR not associated with JA- and C2H4-responsive gene activation

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

But expression of this (and not others) is potentiated in plants undergoing ISR Van Wees et al. (1999) Plant Mol Biol 41:537-549

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. 2000 Physiol. Mol. Plant Pathol. 57:123-134)

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

MYC2 transcription factor involved in priming induced systemic resistance

Pozo. 2008. New Phytol. 180:511-523

Herbivore induce resistance

Differential JA responses in Col-0 and jin1 plants in local and systemic leaves

Vos. 2013. Front. Plant Sci. 4:539

Production of JA, JA-Ile, OPDA, and ABA in local and systemic Col-0 leaves

Vos. 2013. Front. Plant Sci. 4:539

Effects of P. rapae and ABA on MYC and VSP1 expression

Vos. 2013. Front. Plant Sci. 4:539

Effect of herbivory on P. rapae performance in Col-0, aba2-1, and coi1-1 plants

Vos. 2013. Front. Plant Sci. 4:539

Model for herbivore induced resistance in Arabidopsis

Vos. 2013. Front. Plant Sci. 4:539

Comparison of SAR, HIR, and ISR mechanisms

Pieterse et al. (2014) Annu. Rev. Phytopathol. 52:347-75

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?