Plants have array of defense response against biotic stresses which could be either structural reinforcement, release of chemicals, and defense gene expression against invading organisms. The physical barriers are trichoms, waxy cuticle, thick cell wall. Once the pathogen overcomes the first line of defense, basal or innate defense response comes into play. Pathogens secrete some conserved molecules known as Pathogen Associated Molecular Pattern (PAMP/MAMP), which are recognized by transmembrane receptors present in the plasma membrane and initiate a series of signal cascade reaction which ultimately leads to activation of various defense related genes. Apart from inducing the expression of defense related genes, it also triggers a hypersensitive reaction (HR) which cause deliberate cell death at the site of infection and limit the pathogen access to water and nutrient by sacrificing a few cells in order to save the rest of the plant. Once HR is triggered, plant tissue may become highly resistant to a broad range of pathogens for an extended period of time. This phenomenon is called Systemic Acquired Resistance (SAR). Plants respond to herbivory is a similar manner as described above. The biochemical mechanisms of defense against the herbivores are wide-ranging, highly dynamic, and are mediated both by direct and indirect defenses. The defensive compounds are either produced constitutively or in response to plant damage, and affect feeding, growth, and survival of herbivores. In addition, plants also release volatile organic compounds that attract the natural enemies of the herbivores. These strategies either act independently or in conjunction with each other. However, our understanding of these defensive mechanisms is still limited. Induced resistance could be exploited as an important tool for the pest management to minimize the amounts of insecticides used for pest control. Host plant resistance to insects, particularly, induced resistance, can also be manipulated with the use of chemical elicitors of secondary metabolites, which confer resistance to insects. By understanding the mechanisms of induced resistance, we can predict the herbivores that are likely to be affected by inducing responses. The elicitors of induced responses can be sprayed on crop plants to build up the natural defense system against damage caused by herbivores. The induced responses can also be genetically engineered, so that the defensive compounds are constitutively produced in plants challenged by the herbivory. Induced resistance can be exploited for developing crop cultivars, which readily produce the inducible response upon mild infestation, and can act as one of components of integrated pest management for sustainable crop production.

1. Friday, September 23, 2016
CREDIT SEMINAR
Topic: Molecular basis of plant defense against biotic stress
Presented By: Deba Jit Das
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2. Friday, September 23, 2016
Contents of the talk
 Introduction about biotic stress
 Plant defense against pathogens
 Plant defense against insect herbivores
 Case study
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3. Friday, September 23, 2016
Plant defense against
pathogens
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4. What are the challenges of plants?
 Being sessile in nature, plants are
exploited as a source of food and shelter
by all parasites
 Plants have evolved sophisticated defense
mechanisms to fight against their enemies
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5. How plant pathogens can be grouped???
 Pathogens can be any agents that causes infections or diseases specially micro organisms
 Pathogens can be of different types, such as
Biotrophic: Fungus Bleumeria graminis, bacteria Xanthomonas oryzae
Necrotrophic: Fungus Magnaporthe grisea
Hemibiotrophics: Gray mold fungus Botrytis cinerea, bacteria Erwinia
carotovora
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6. Friday, September 23, 2016
What are the plant defense responses?
 Hypersensitive response
 Production of reactive oxygen species
 Cell wall fortification
 Production of antimicrobial metabolites (phytoalexins)
 Defense signal transduction
 Synthesis of enzymes harmful to pathogen (eg. chitinases, glucanases)
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7. Friday, September 23, 2016
How does plants defend themselves against pathogens???
 Physical barrier: Leaf hairs, wax, thick cell wall, cuticle, antimicrobial compounds such as
phytoalexins etc
 Basal resistance or innate immune response:
1. PAMP-triggered immunity (PTI)
2. Effector Triggered Immunity (ETI)
 Hyper sensitive response and activation of SAR
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8. Friday, September 23, 2016
What is basal resistance?
 Triggered by trans-membrane receptors that recognize conserved molecules released by a
variety of (unrelated) microbes
 Include cell wall fragments, chitin or peptide motifs in bacterial flagella - PAMPs or
MAMPs
 PAMP- triggered immunity (PTI)
(Liu et al.,2008)
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9. Friday, September 23, 2016
What are the different Receptor proteins?
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10. Friday, September 23, 2016
What are the different elicitors of pathogens??
 Any substance that has the capability of activating defense responses in plants
 Include components of the cell surface as well as excreted metabolites
Elicitors
General Race specific
a) Oligosaccharide elicitors a) avr gene products
b) Protein/peptide elicitors
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11. Friday, September 23, 2016
Phases of pathogen triggered immunity
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12. Friday, September 23, 2016
 Flagellin Sensing 2 (FLS2) is a leucine- rich repeat receptor kinase (LRR-RK) that binds to
Flg22. and confers recognition specificity.
 Arabidopsis LRR-RK EFR binds bacterial EF-Tu
 The tomato LRR receptor-like proteins EIX1/2 recognizes fungal xylanase.
 Rice LysM domain containing receptor-like protein (RLP) CEBiP binds fungal chitin.
Examples of PAMP triggered immunity
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13. Friday, September 23, 2016
What is secondary defense of plants??
 Against virulence effector proteins produced by pathogens
 Effector –triggered immunity (ETI)
 Mediated by resistance (R) proteins
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14. Friday, September 23, 2016
Formation of active PRR complex
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15. Friday, September 23, 2016
Examples of resistance genes
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16. Friday, September 23, 2016
Models of pathogen recognition by plants
 Three different models has been postulated
(I) Gene for gene resistance model
(a) Elicitor-Suppressor model
(b) Elicitor-Receptor model
(II) Guard model
(III) Decoy model
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17. Friday, September 23, 2016
Gene for gene resistance model
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18. Friday, September 23, 2016
Guard and Decoy model
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19. Friday, September 23, 2016
Evidence of Guard hypothesis
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20. Friday, September 23, 2016
Molecular mechanism of plant defense against Biotrophs and Necrotrophs??
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21. Friday, September 23, 2016
How does SA, JA ant ET activate defense responsive genes??
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22. Friday, September 23, 2016
Plant defense against
herbivores
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23. Friday, September 23, 2016
How does plants recognize herbivore attack??
Recognition of Insect Herbivore Attack
Insect Oral
Secretions
Ovipositional
Fluids
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24. Friday, September 23, 2016
What are the Herbivores associated elicitors??
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25. Friday, September 23, 2016
How does plant react against insect Oviposition??
 Insect oviposition fluids can give rise to
defense responses in the plant
 Many female adult herbivorous insects
lay eggs directly into plants, and some
species are known to perceive insects’
oviposition activities and deploy
defenses responses
Oviposition by Pieris brassicae causes hypersensitive response on
Arabidopsis
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26. Friday, September 23, 2016
Oviposition induced plant responses against herbivores
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27. Friday, September 23, 2016
How does plants defend themselves against herbivores??
 Plants produces different kinds of defensive compounds upon insect infestations
 Plants releases volatile organic compounds that attract
 Insect infestation leads to activation of different signaling pathways
 Production of Reactive Oxygen Species (ROS)
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28. Friday, September 23, 2016
Hypersensitive response against oviposition
Egg of small cabbage white butterfly, inducing hypersensitive
response–like necrosis in Brassica nigra.
Egg of Heliothis subflexa inducing neoplastic growth in Physalis
angulata leaf.
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29. Friday, September 23, 2016
What are the changes occur in plant??
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30. Friday, September 23, 2016
What are the different types of defense responses against herbivores??
Defense responses
Direct defense
Indirect
defense
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31. Friday, September 23, 2016
What are the direct defense responses??
 The term “direct defense” is used when plants produce physical barriers against insect
herbivores, or compounds that exert repellent, antinutritive or toxic effects on the
herbivores themselves
 Bioactive Specialized Compounds
 Hypersensitive response
 Digestibility Reduction
 Reallocation of Resources
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32. Friday, September 23, 2016
How does bioactive specialized compounds inhibit insect infestation?
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33. Friday, September 23, 2016
What are the digestibility reducing compounds??
 Plants produce a number of defense compounds that reduce insect herbivores ability to
digest the plant derived nutrients
 Proteinase Inhibitors-inhibit proteases
 α-amylase inhibitors-inhibit carbohydrate digestive enzymes
 Lectins-binds to mebrane glycosyl group
 Chitinases-disrupts gut peritrophic membrane
 Polyphenol oxidases- Antinutritive enzyme
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34. Friday, September 23, 2016
Indirect defense response
 The term “indirect defense” is used when plants attract, nourish or house other organisms to
reduce enemy pressure.
 Herbivore-induced plant volatiles
 Extrafloral Nectar
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35. Friday, September 23, 2016
Herbivore induced plant volatile
 Herbivore-induced plant volatiles (HIPV) can mediate indirect defenses, i.e., by attracting
foraging carnivorous predators and parasitoids that kill herbivores
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36. Friday, September 23, 2016
Examples of HIPV
HIPVs Plant Herbivore Natural Enemy
β-caryophyllene
β-ocimene
Tobacco H. virescens Cardiochiles nigriceps
(E)-β-farnesene
(E)-caryophyllene
(E)-α-bergamotene
Maize S. littoralis Cotesia marginiventris
(E)–4,8–dimethyl-1,3,7-nonatriene Maize M. separata Exorista japonica
Cotesia kariyai
linalool
α-pinene
1-hexanol
Maize M. separata Exorista japonica
Campoletis chlorideae
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37. Friday, September 23, 2016
Extrafloral Nectar
 Extrafloral nectar (EFN) appear in more than 70 plant species spanning angiosperms,
gymnosperms and ferns, indicating that it is evolutionary more ancient than floral nectar
 In contrast to floral nectar, used to attract pollinators, EFN is secreted on leaves and
shoots to attract predators and parasitoids
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38. Friday, September 23, 2016
Extrafloral nectar as an herbivore-induced defense trait
Family Species Herbivore Trait enhanced
Bignoniaceae Catalpa bignonioides
(Indian bean)
Ceratomia catalpae
(Catalpa Sphinx)
Sugar content in EFN
Euphorbiaceae Ricinus communis
(Castor)
Spodoptera littoralis EFN volume
Euphorbiaceae Triadica sebifera
(Chinese tallow tree)
Gadirtha inexacta,
and
Grammodes geometrica
Secretion of total solids
Malvaceae Gossypium herbaceum
(Cotton)
Spodoptera littoralis EFN volume
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39. Friday, September 23, 2016
Mechanism of JA signaling upon insect attack??
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40. Friday, September 23, 2016
What are the systemic response of plant against herbivores??
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41. Friday, September 23, 2016
Regulation of defense response
 Levels of jasmonic acid rise in response to herbivor damage
 This hormone can trigger many types of plant defenses including bioactive compounds
 The action of jasmonic acid induces the transcription of many genes involved in plant defense
 Jasmonic acid turns on genes for proteinase inhibitor.
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42. Friday, September 23, 2016
JA regulated defense responsive genes
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43. Friday, September 23, 2016
JA regulated defense responsive genes
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44. Friday, September 23, 2016
Case study
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45. Friday, September 23, 2016 45

46. Friday, September 23, 2016
Introduction
 Alternaria black spot (causal organism- Alternaria brassicae) an important disease of rape
seed and mustard (Brassica juncea) in India
 Wild relative of mustard namely Sinapis alba is known to moderately resistant against the
pathogen.
 Expression different types of PR-genes upon infection by the pathogen have been reported
 Different signaling hormones also activates the plant defense system
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47. Friday, September 23, 2016
Objectives of the study
 To see the differential expression of five defense related genes namely, PR1, PR2, PR3,
PDF1.2 and NPR1 in both susceptible and moderately resistant genotypes under two
different treatments.
 Spray with conidial suspension of A. brassicae
 Exogenous application defense inducing hormones
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48. Friday, September 23, 2016
Materials and methods
1. Plant material and A. brassicae inoculation
 B. juncea and S. alba plants were raised from seeds in pots containing a mixture of soil
and organic manure (2: 1)
2. Conidial suspensions were prepared by scraping mycelium from 21-day old cultures and
suspending in sterilized distilled water
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49. Friday, September 23, 2016
Plant treatments
Treatments
Treatment 1: Plants
inoculation with 4-6 drops
(10ul) pathogen inoculum
Treatment 2: Spray with 2
mM SA and 100 uM JA
Pretreatment prior to
inoculation: Spray with 2 mM
SA and 100 uM JA and
Combination of SA and JA @
1mM and SA+50uM JA
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50. Friday, September 23, 2016
Lists of primers used for RT-PCR
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51. Friday, September 23, 2016
Results of the experiment
1. Disease Scoring
Fig: In planta challenge of B. juncea and S. alba with A. brassicae; (a) B. juncea mock control, (b and c) B. juncea- 5
days after infection with A. brassicae, (d) S. alba mock control, (e and f) S. alba- 5 days after infection with A.
brassicae
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52. Friday, September 23, 2016
Results of the experiment
2. A.brassicae induced defense genes
Transcript accumulation in A. brassicae inoculated local leaves Transcript accumulation in un-inoculated distal leaves
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53. Friday, September 23, 2016
Results of the experiment
3. SA and JA induced defense genes
Transcript accumulation in SA treated leaves Transcript accumulation in JA treated leaves
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54. Friday, September 23, 2016
Results of the experiment
4. Effect of JA, SA and SA+JA on lesion developed by A. brassicae
Protective effect of exogenously applied SA or JA on infection by A.
brassicae in B. juncea
Protective effect of exogenously applied SA or JA on infection by A.
brassicae in S. alba
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55. Friday, September 23, 2016
I can fight too with
my enemies…Come
on…lets see…
Thank you very much for
your kind attention…..
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