Credit seminar

Wednesday, May 3, 2023 1

CREDIT SEMINAR

Topic: Molecular basis of plant defense against biotic stress

Presented By: Deba Jit Das


Contents of the talk Introduction about biotic stress

Plant defense against pathogens

Plant defense against insect herbivores

Case study


Plant defense against pathogens


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


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


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)


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


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)


What are the different Receptor proteins?

10Wednesday, May 3, 2023

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


Phases of pathogen triggered immunity


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


What is secondary defense of plants??

Against virulence effector proteins produced by pathogens

Effector –triggered immunity (ETI)

Mediated by resistance (R) proteins


Formation of active PRR complex


Examples of resistance genes


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


Gene for gene resistance model


Guard and Decoy model


Evidence of Guard hypothesis


Molecular mechanism of plant defense against Biotrophs and Necrotrophs??


How does SA, JA ant ET activate defense responsive genes??


Plant defense against herbivores


How does plants recognize herbivore attack??

Recognition of Insect Herbivore Attack

Insect Oral Secretions

Ovipositional Fluids


What are the Herbivores associated elicitors??


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


Oviposition induced plant responses against herbivores


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)


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.


What are the changes occur in plant??


What are the different types of defense responses against herbivores??

Defense responses

Direct defenseIndirect defense


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


How does bioactive specialized compounds inhibit insect infestation?


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 proteasesα-amylase inhibitors-inhibit carbohydrate digestive enzymes

Lectins-binds to mebrane glycosyl groupChitinases-disrupts gut peritrophic membrane Polyphenol oxidases- Antinutritive enzyme


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


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


Examples of HIPVHIPVs 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


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


Extrafloral nectar as an herbivore-induced defense traitFamily 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,andGrammodes geometrica

Secretion of total solids

Malvaceae Gossypium herbaceum(Cotton)

Spodoptera littoralis EFN volume


Mechanism of JA signaling upon insect attack??


What are the systemic response of plant against herbivores??


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.


JA regulated defense responsive genes


JA regulated defense responsive genes


Case study



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


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


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


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


Lists of primers used for RT-PCR


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


Results of the experiment2. A.brassicae induced defense genes Transcript accumulation in A. brassicae inoculated local leaves Transcript accumulation in un-inoculated distal leaves


Results of the experiment3. SA and JA induced defense genes

Transcript accumulation in SA treated leaves Transcript accumulation in JA treated leaves


Results of the experiment4. 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


I can fight too with my enemies…Come

on…lets see…

Thank you very much for your kind attention…..

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