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Induced Systemic Resistance (ISR). Plant responses to plant growth promoting rhizobacteria. Priming. Conrath 2009. Properties of PGPR. Stimulate growth N fixation Increase solubility of limiting nutrients ( siderophores ) Stimulate nutrient delivery and uptake

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slide1

Induced Systemic Resistance

(ISR)

  • Plant responses to plant growth promoting rhizobacteria
slide2

Priming

Conrath 2009

slide3

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
slide4

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

slide5

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 81:728-734

slide6

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

slide8

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
slide9

Changes in gene expression in bacterized plants

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

slide10

Specificity in ISR induction by Pseudomonas spp. strains

Root colonization is similar in all cases

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

slide12

ISR is SA-independent

W

Fusarium

W

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

P. syringae

slide13

ISR is independent of PR gene activation

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

*just prior to challenge inoc

slide14

ISR requires JA and C2H4 response pathways

etr1

nahG

npr1

ISR

SAR

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

slide15

ISR requires JA and C2H4 response pathways

in that order

etr1

jar1

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

slide17

?

?

Pieterse et al (2002) Plant Biology 4:535-544

slide18

But expression of this (and not others) is potentiated in plants undergoing ISR

Van Wees et al. (1999) Plant Mol Biol 41:537-549

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

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)

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

slide19

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

slide20

Pieterse et al. WORKING MODEL

Pieterse (2001) Eur. J. Plant Pathol. 107:51-61

slide21

ISR vs. SAR

Induced systemic resistance is induced by non-pathogenic rhizobacteria

  • Systemic acquired resistance is induced systemically after inoculation with necrotizing pathogens, HR, or application of some chemicals (SA analogs or agonists)

Induced systemic resistance is independent of salicylic acid, but involves jasmonic acid and ethylene signaling

  • Systemic acquired resistance requires salicylic acid as signaling molecule in plants

Induced systemic resistance is accompanied by the expression of sets of genes distinct from the PR genes

  • Systemic acquired resistance is accompanied by induction of pathogenesis
  • related proteins

Both require NPR1

slide23

Discussion

1) possible mechanisms of ISR

2) selective advantage to the plant and practical significance

3) Some biocontrol fungi induce defenses that resemble ISR induced by PGPR

slide25

(There may be a) parallel ethylene-inducible defensive pathway that does not require NPR. A candidate pathway might be the ethylene-inducible pathway leading to Pdf1.2 gene expression that has been shown to be NPR1 independent (Penninckx et al. 1996 ). Alternatively, this low level of protection in npr1 plants may be caused by the twofold higher production of ethylene after ACC treatment (Figure 2B). However, the latter possibility seems unlikely because a twofold increase in ethylene production in wild-type Col-0 plants, by applying 2.5 mM ACC to the leaves instead of 1 mM, does not result in a higher level of protection against P. s. tomato infection (S.C.M. van Wees, unpublished results). In itself, the enhanced level of ethylene production in ACC-treated npr1 plants is intriguing because it demonstrates that npr1 plants show twofold higher ACC oxidase activity than do wild-type plants. Interestingly, pathogen infection also causes a significantly higher increase in ethylene production in npr1 plants (C.M.J. Pieterse, unpublished results), suggesting that not only SA responsiveness but also ethylene metabolism is altered by the npr1 mutation.

ISR requires JA and C2H4 response pathways

in that order

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

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