Systemic acquired Resistance

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1. welcome

2. Presented by Mukesh Kumar ( Ph.D Scholar) Department of Plant Pathology Dr. Rajendra Prasad Central Agricultural University Pusa , Samastipur , 848185 (Bihar) India Credit Seminar on “Systemic Acquired Resistance”

3. Ist recognized as a significant phenomenon in 1933 by Chester . Infection of plants with necrotizing pathogens (causing HR) often results in enhanced resistance to subsequent infections by a variety of fungal, bacterial and viral pathogens. This physiological immunity was termed Systemic Acquired Resistance (SAR) . SAR confers a broad spectrum type of resistance SAR is effective against some but not all pathogens: Tobacco: Phytophthora parasitica , Cercospora nicotianae , Peronospora tabacina tobacco mosaic virus, tobacco necrosis virus, Pseudomonas syringae pv . tabaci , Erwinia carotovora Not effective against: Botrytis cinerea or Alternaria alternata Arabidopsis: Phytophthora parasitica turnip crinkle virus Pseudomonas syringae pv . tomato DC3000 iNTRODUCTION

4. SAR (Systemic Acquired Resistance) Systemic acquired resistance (SAR) is a mechanism of induced defense that confers long-lasting protection against a broad spectrum of microorganisms. SAR requires the signal molecule salicylic acid (SA) and is associated with accumulation of pathogenesis-related proteins , which are thought to contribute to resistance . or Resistance triggered in the plant during its life time is Acquired Resistance . It can be local (LAR) confined to few cells or tissues, or systemic (SAR) having been moved through out the plant. Systemic acquired resistance (SAR) refers to a distinct signal transduction pathway that plays an important role in the ability of plants to defend themselves against pathogens

5. Frank Ross (1961) showed that tobacco plants challenged with tobacco mosaic virus (TMV) subsequently developed increased resistance to secondary infection in distal tissues. This spread of resistance throughout the plant’s tissues was termed systemic acquired resistance (SAR ). SAR is characterized by the increased expression of a large number of pathogenesis-related genes ( PR genes), in both local and systemic tissues. PR proteins were first described in the 1970s by Van Loon, who observed accumulation of various novel proteins after infection of tobacco with TMV. History

6. White 1979 observed that PR protein accumulation and resistance to TMV could be induced by treatment of tobacco with salicylic acid (SA), aspirin ( acetyl SA ), or benzoic acid. Malamy et al ., 1990 Evidence that SA is a signal for the induction of SAR. Malamy et al . 1990 : showed that the endogenous SA concentration rises in both local and systemic tissues after infection of tobacco with TMV and this rise correlates with PR gene induction. Metraux et al . 1990 : found that cucumber plants infected with either Colletotrichum lagenarium or tobacco necrosis virus (TNV) have considerably elevated levels of SA in the phloem sap. A requirement for SA as an endogenous signal for SAR was proven by Gaffney et al . 1993 using a bacterial gene, nahG , encoding salicylate hydroxylase, which removes SA by conversion to catechol

7. ISR SAR Induced Systemic Resistance Systemic Acquired Resistance SA independent SA dependent Necrosis reaction absent Necrosis reaction present Signaling molecules JA, Ethylene Signaling molecules SA More elastic Less elastic Against necrotrophs and insects Against biotrophs Continuous irritation is required Not required Defense genes involved PR-proteins Difference between ISR and SAR 07/06/2017 7:49 PM 7 Dept. of Plant Pathology

8. Characteristics of SAR Resistance is expressed against broad spectrum of organism Time needed for establishment of SAR depend on both the plant and type of inducing factor. It need for a necrotic lesions produced by the pathogen as an inducing agent. Systemic expression of PRP genes . Involvement of salicylic acid as apart of signaling process.

9. Systemic Acquire Resistance (SAR) Secondary response Systemic Broad-range resistance Leads to Pathogenesis-Related (PR) gene expression Signals: SA ,

10. Mechanism Pathogen induced localized necrosis EDS / SID 1 SID 2 NPR 1 SA accumulation NIM 1 Resistance (Enhanced disease susceptibility) (Salicylic acid induction deficient) (No PR 1 expression) (Non inducable immunity)) PRPs Post challenge defence Eg:Arabidopsi s

11. NPR1 The Arabidopsis NPR1 gene is a positive regulator of inducible plant disease resistance. Expression of NPR1 is induced by pathogen infection or treatment with defense-inducing compounds such as salicylic acid (SA). Transgenic plants overexpressing NPR1 exhibit enhanced resistance to a broad spectrum of microbial pathogens. Whereas plants under expressing the gene are more susceptible to pathogen infection. These results suggest that regulation of NPR1 gene expression is important for the activation of plant defense responses.

12. NPR1: non-expresser of PR genes Also known as NIM1 or SAI1 Positive regulator of SAR Downstream of SA, upstream of PR genes npr1 mutants are susceptible to various pathogens Over expression of NPR1 generates broad-spectrum resistance Unique, but similar to I κ -B (negative regulator of immunity in animals)

13. NPR1 overexpression

14. Salicylic acid SA/ orthohydroxy benzoic acid- group of phenolics Induced resistance becomes systemic SAR- endogenous signal produced by infected leaf and translocate in the phloem to other plant parts Vascular mobile signal that moves throughout the plant after initial infection It is reported in several plant species like tomato, potato, pea, sunflower etc. Salicylate regulated defenses more active against biotrophic pathogens

15. Salicylic Acid (SA)-mediated SAR Salicylic acid is part of signaling pathway involved in transmission of the defense response throughout the plant to produce SAR SA reported as the endogenously as well as exogenously signal of SAR ( Metraux et al ., 1990, Sticher , 1997) SA plat role in elicitation of Pathogenesis-Related proteins Analogs: INA or BTH

16. Salicylic Acid Biosynthesis Genetic studies in  Arabidopsis  have shown that SA is synthesized mainly through the pathway involving ICS1 Biochemically, SA can also be synthesized from phenylalanine ammonia lyase (PAL) but this pathway seems to play a minor role in SAR-associated SA synthesis. The chorismate pathway has similarities to the bacterial SA-biosynthesis pathway: ICS1 converts chorismate to isochorismate SA is generated from isochorismate catalyzed by isochorismate pyruvate lyase (IPL) .

17. Mutants affecting SA synthesis Elevated SA accumulation dnd1 ( defense, no death 1 ): increased SA, but reduced HR, DND1 gene encodes cyclic-nucleotide-gated ion channel mpk4 : constitutive SA accumulation edr1 ( enhanced disease resistance 1 ): defective MAPKKK

18. Systemin Plant peptide hormone involved in the wound response in the Solanaceae family. Isolated- tomato leaves in 1991 by a group lead by Clarence A. Ryan Systemin induces the production of protease inhibitors which protect against insect herbivores, other peptides activate defensins and modify root growth.

19. Benzothiadiazole (BTH) BTH also is a activator of the SAR pathway. However, BTH treatment induces both PR-1 mRNA accumulation and P. parasitica resistance in transgenic Arabidopsis expressing nahG gene, indicating that BTH action does not required SA accumulation.

20. Peronospora parasitica

21. Involvement of H 2 O 2 in SAR Elevated level of cellular reactive oxygen species (i.e., H 2 O 2 ) was observed in plants with SAR. Chen and Klessig (1993) isolated a SA-binding protein (SABP) from the cDNA library of tobacco leaves. The deduced cDNA sequence indicates that SABP is a catalase . They proposed that SA activates the elevated levels of cellular H 2 O 2 by inhibiting the catalase activity. Cellular H 2 O 2 functions as a secondary messenger in SAR signal transduction.

22. Production of pathogenesis related protein PR protein are plant protein that are induced in pathological and related situation. These proteins are accumulated 7-10 days after infection and indicate the attainment of SAR. It is accumulated in the intercellular spaces(first line of defence) and vacuole (second line of defence by lytic enzyme).

23. Salicylic acid (SA) treatment delays the onset of Cucumber mosaic virus (CMV)-induced disease symptoms in squash ( Cucurbita pepo ). Symptom development was monitored in squash plants inoculated.

24. SAR induced by TNV against C. lagenarium in cucumber. Leaf 1 was challenged with the fungus between 2 and 5 d after primary inoculation of the cotyledon with TNV (filled bars) or mock inoculation with water (open bars).

25. 31 Peng et al ., 2013

26. The positives aspects of SAR…. Broad spectrum , thus effective against viral, bacterial and fungal pathogen. Its ability to immunize susceptible plants implies that genetic potential for resistance is in all types of plants. The significant practical aspects of SAR is the discovery of chemical inducers of plant defense. Dichloro isonicotinic acid (DCINA) provides systemic protection , as provided by biotic agents. New generation fungicides act as a plant defense system , rather than killing pathogen. ICGA-245 704, a benzothiadiazole compound (plant activator) switches SAR in host plant.

27. Conclusion Systemic acquired resistance is a general and rather elegant response developed by plants against various invaders. Better understanding of the SAR signaling pathway will certainly lead to new environmentally friendly methods of crop protection. Systemic acquired resistance (SAR) is a highly desirable form of resistance that protects against a broad-spectrum of related or unrelated pathogens. SAR involves the generation of multiple signals at the site of primary infection, which arms distal portions against subsequent secondary infections.

28. Thank you