Induced systemic resistance (ISR) mechanism

Description of Induced resistance in plants

1. ISR (INDUCED SYSTEMIC RESISTANCE) COURSE : PAT-515, BIOLOGICAL CONTROL OF PLANT DISEASES. COURSE TEACHER: DR.E.G.EBENEZAR. SUBMITTED BY: A.VEDASREE.

2. Def: Induced state of resistance in plants triggered by biological or chemical inducers, which protects non-exposed plant parts against future attack by pathogenic microbes and herbivorous insects. INDUCED RESISTANCE:

3. CHARACTERISTICS OF INDUCED RESISTANCE As a result of infection by a pathogen, insect herbivory, colonization of the roots by specific beneficial microbes or after treatment with specific chemicals. Activation of latent defense mechanisms that are expressed upon a subsequent challenge from a pathogen or insect herbivore.

4. It is expressed not only at the site of induction but also systemically in all plant parts It is regulated by a network of interconnected signaling pathways in which plant hormones play a major regulatory role PTI and ETI trigger an induced resistance PTI – PATHOGEN TRIGGERED IMMUNITY ETI – EFFECTOR TRIGGERED IMMUNITY

5. Induced resistance involves long-distance signals signals are transported through the vascular system or as airborne signals, systemically propagate an enhanced defensive capacity against a broad spectrum of attackers in healthy plant parts. Consequently, secondary (2 ◦) pathogen infections or herbivore infestations of induced plant tissues cause significantly less damage than those in primary (1 ◦) infected or infested tissues.

6. TYPES: LOCALIZED INDUCED RESISTANCE, SYSTEMIC INDUCED RESISTANCE.

7. SYSTEMIC INDUCED RESISTANCE THERE ARE THREE TYPES: SAR (systemic acquired resistance) ISR (induced systemic resistance) HIR ( herbivore induced resistance)

8. SAR (SYSTEMIC ACQUIRED RESISTANCE) DEF: Enhanced defensive capacity of the entire plant against a broad spectrum of pathogens; acquired upon local induction by a pathogen

9. SAR

10. Onset of pathogen-induced SAR is triggered upon local activation of a PTI or ETI response In systemic tissues, SAR is characterized by increased levels of the hormone salicylic acid (SA). SAR is accompanied by the coordinate activation of PATHOGENESIS-RELATED (PR) genes.

11. SAR signaling downstream of SA is controlled by NONEXPRESSOR OF PR GENES1 (NPR1), which upon activation by SA acts as a transcriptional coactivator of PR genes Signals : methyl ester of SA ( MeSA ), the diterpenoid dehydroabietinal (DA), a glycerol-3-phosphate (G3P)-dependent factor, azelaic acid ( AzA ), and pipecolic acid (Pip) .

12. Fig: Current model of signal-transduction pathways leading to pathogen-induced systemic acquired resistance (SAR) and rhizobacteria -induced systemic resistance (ISR). ISR SAR

13. ISR (INDUCED SYSTEMIC RESISTANCE) DEFINITION ISR is a phenomenon where plants inoculated with beneficial microbes produce a signal compound that is transported systemically through out the plant and activates its defense mechanism (making the entire plant resistant to subsequent infection) without its own physical presence at the site.

14. Enhanced defensive capacity of the entire plant against a broad spectrum of pathogens; acquired upon local induction by beneficial microbes It is induced by certain rhizobacteria that do not cause a necrotic leisions . Eg ; PGPR Resistance induction is not by the PRPs.

15. Here it depends upon the perception of ethylene and jasmonic acid rather than salicylic acid as a signal for resistance expression. Some non-pathogenic rhizobacteria may trigger a SA-dependent signalling pathway that leads to a state of induced resistance resembling SAR (After Pieterse et al., 1998).

16. HISTORY I nduced resistance in plants were reported as early as the late 1800s and early1900s ( Beauverie , 1901; Ray, 1901; Chester, 1933). Muller and Borger (1940) described carefully conducted experiments which established the phenomenon of induced local resistance (ILR) in potatos to late blight (Phytophthora infestans ). Induced systemic resistance (ISR) was analytically established by Ku´c et al.,(1959) and Ross (1966).

17. Ku´c et al., (1959) and Maclennan et al. (1963) demonstrated that apple plants were made systemically resistant to apple scab (Venturia inaequalis ) by infiltrating lower leaves with D-phenylalanine, D- alanine and amino isobutyric acid (AIB). The amino acids did not inhibit the growth of V. inaequalis in vitro at concentrations used for infusion. Ross (1966) and coworkers demonstrated that inoculation of lower leaves of tobacco with a local lesion strain of tobacco mosaic virus (TMV) systemically enhanced resistance to the same strain of the virus.

18. Induced Systemic Resistance (ISR) is potentiated by Plant Growth-Promoting Rhizobacteria (PGPR), of which best characterized are strains that belong to genus Pseudomonas that cause no visible damage to the plant’s root system. Unlike SAR, ISR does not involve the accumulation of pathogenesis-related proteins or salicylic acid, but instead, relies on pathways regulated by jasmonate and ethylene .

19. The most widely studied group of PGPB is plant growth-promoting rhizobacteria (PGPR) that colonize the root surface and the closely adhering soil interface, the rhizosphere . The PGPR, P. fluorescens GRP3 showed ISR in rice against sheath blight. The plant-growth stimulating volatile 2,3-butanediol that is found in Bacillus spp can also initiate ISR. ISR is more active against nectrotrophic pathogens.

20. Properties of PGPR Stimulate growth Nitrogen fixation Increase solubility of limiting nutrients ( Siderophores ) Stimulate nutrient delivery and uptake Production of phytohormones Modulation of plant development ( e g : reduce ethylene and enhance root growth) Plant mediated disease suppression Non-pathogens antagonize pathogens (Competition, antibiotics) Activating plant to better defend itself (ISR) Induced resistance observed on spatially separated parts of same plant.

21. Characteristics of induced systemic resistance Induced Systemic Resistance is active against fungi, bacteria, viruses & sometimes nematodes and insects. Induced systemic resistance is maintained for prolonged periods.

22. MECHANISM OF ISR Structural and ultra-structural cell wall modifications in the host plants protecting cell walls against the spread of a pathogen ( deposition of newly formed callose and accumulation of phenolic compounds at the site of penetration of invading hyphae Biochemical/Physiological changes in the host plants Plant defense proteins and enzymes. ISR (Induced Systemic Resistance) primes plant for enhanced ethylene production SAR plants do not show increased levels of ethylene or Jasmonic acid (JA), but ISR activated plants convert more 1-aminocyclopropane-1-carboxylate (ACC) to ethylene.

23. JASMONIC ACID JA was first isolated from cultures of the fungus Lasiodiplodia theobromae . Derivatives of JA - tuberonic acid and cucurbic acid Tuberonic acid regulate tuber formation in potato The highest levels of JA/ JAMe are reported in flowers and reproductive tissues and lower levels are found in roots and mature leaves JA - 10ng to as much as 3μg/g fresh weight in different tissues Jasmonate regulated defenses more active against necrotrophic pathogens.

24. BIOSYNTHESIS OF JASMONIC ACID

25. ETHYLENE It is a volatile hormone derived from methionine and involved in numerous physiological processes Induce the PRs- β 1,3 glucanase and chitinase Structural reinforcement of the cell wall; such as lignification and accumulation of HRGP Melon- petiole treated with elicitor, induced ethylene and HRPG ACC-precursor of ethylene.

26. Biosynthesis of ethylene:

27. ROLE OF ISR Defence Against Necrotrophs . Developmental: linked to growth promotion- escape Physiological: reduced symptom expression- tolerance. Environmental : associated with microbial antagonism in the rhizosphere. Biochemical : resistance- Induction of cell wall reinforcement Induction of phytoalexins Induction of pathogenesis related proteins “Priming” of defense responses (Resistance). ISR (Induced Systemic Resistance) Primes Plant For Enhanced Ethylene Production.

28. ADVANTAGES MORE SUSTAINABLE REDUCE ENVIRONMENTAL POLLUTION INCREASED BIO DIVERSITY MORE TARGET SPECIFIC BETTER YIELDS

29. DISADVANTAGES ACCUMULATION OF UNDESIRABLE SECONDARY METABOLITES. LOW MOLECULAR ELICITORS ARE NOT AVAILABLE. CAUSE SUBSTANTIAL YIELD BECAUSE OF HIGH ENERGY DEMANDING PROCESS.

30. CONCLUSION ISR-WIDELY OBSERVED PHENOMENON IN PLANTS. SEVERAL PSEUDOMONAS SPP. HAVE BEEN REPORTED TO INDUCE SYSTEMIC RESISTANCE JA AND ETHYLENE ARE THE MAJOR SIGNALLING MOLECULES.

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