Induced Systemic Resistance (ISR) - Plant responses to plant growth promoting rhizobacteria - Herbivore induced resistance Biologically induced systemic resistance Pieterse et al. (2014) Annu. Rev. Phytopathol. 52:347-75 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 Nonbacterized Bacillus pumulis strain SE34 Kloepper. 2004. Phytopathology. 94:1259-1266 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 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 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 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 Changes in gene expression in bacterized plants From Van Loon (2007) Eur. J. Plant Pathol. 119:243-254 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 Model system – Arabidopsis/Pseudomonas fluorescens WCS417r For Control WCS417r Ps – ISR is SA-independent W Fusarium – W P. syringae Pieterse et al. (1996) Plant Cell 8, 1225-1237 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 pathways in 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 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) Pieterse et al. (1998) Plant Cell 10, 1571-158 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?