Welcome

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PLANT DEFENSE RESPONSES TO HERBIVORE INSECTS

H S GADADPGS13AGR5965

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Doctoral seminar-iii

OutlineOutline • Introduction

• Recognition of Insect Herbivore Attack

• Early Events in the Plant defense

• Regulation of Defense Responses

• Types defense Responses

• Conclusion

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Introduction

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Recognition of Insect Herbivore Attack

• Plants have the abil ity to distinguish between herbivory and mechanical damage, such as hail and wind, as well as to recognize ovipositioning

• This feature is needed to avoid wasting expensive

defense resources, s ince production and release of defense responses only benefits herbivore-challenged plants

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Insect Oral Secretions

• Plants are able to recognize compounds in insect oral secret ions, which el icit more intense defense responses

• Compared with the vast diversity of herbivores that attack plants , very few herbivore-derived el icitors are known

• Conjugation of plant- and herbivore-derived precursors result in the formation of fatty acid-amino acid conjugates (FACs)

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Herbivore-associated elicitors

8Bonaventure et al., 2011

Oviposition Fluids

• Insect oviposit ion 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’ oviposit ion activit ies and deploy defenses responses

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Oviposition-induced plant responses acting against the herbivores

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Hilker and Meiners, 2006 11

Cont…

Early Events in the Plant defense

• Successful implementation of an induced defense response requires that plants respond to herbivory both rapidly and accurately

• Early signaling events at the plant-insect interface, which occur well before changes in host plant gene expression and defense-related metabolism

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Events in plants after feeding by insect herbivores

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Membrane potential changes

• The plant plasma membrane is in direct contact with the environment, and is therefore able to recognize outer changes and initiate cascade events leading to a possible defense response

• Herbivore feeding will lead to an immediate change in the cell membrane potential (Vm), or modulate the ion flux at the plasma membrane level

• The Vm changes induced by herbivory are followed by a fast electric signal (action potential) , which travels through the entire plant from the point where the signal was induced 14

Ca2+ Homeostasis• Calcium ions function as a second messenger in

several plant signaling pathways

• In healthy cells , the cytosolic Ca2+ concentration is lower than in the apoplastic fluid, and cellular organelles

• This creates a driving force for the influx of Ca2+ into the cytosol , via channel proteins where it acts as a messenger to induce defense related signals

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Reactive Oxygen Species

• Superoxide anion, hydrogen peroxide , s inglet , and hydroxyl radical are col lect ively cal led ROS

• They are produced in mitochondria , chloroplasts , and peroxisomes, as well as on the external surfaces of plasma membranes

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Calcium variations in Maidenhair tree upon mechanical damage and herbivore wounding

Mohanta et al., 201217

H2O2 variations in Maidenhair tree upon mechanical damage and herbivore wounding

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MAPK Signaling

• Mitogen-activated protein kinase (MAPK) cascades are important pathways for downstream sensors and receptors that regulate cel lular responses to insect attack

• MAPK signall ing induces the biosynthesis of jasmonic acid

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Tomato MAPKs function in the systemin-mediated defense response against herbivorous insects

Kandoth et al., 2007

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Systemic Signaling

• In plants attacked by insect herbivores, the expression of several defense genes is induced in undamaged leaves

• Several components have been identified that are involved in the systemic induction of defense responses

• Systemin peptides• Oligogalacturonides (OGAs)• Jasmonates 21

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Regulation of Defense Responses

Levels of jasmonic acid r ise 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 . 23

Model of jasmonate regulation of defense responsive genes

Lee et al., 2010

24a) Resting stage b) Response to herbivore wounding

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(c) In the presence of (+)-7-epi-JA-L-Ile and the absence of gibberellic acids (d) If GAs are present, they will bind to DELLA and trigger degradation

Types of Defense Responses

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Direct Defense Response

The term “direct defense” is used when plants produce physical barriers against insect herbivores , or compounds that exert repellent, antinutrit ive or toxic effects on the herbivores themselves

• Bioactive Specialized Compounds• Hypersensitive response

• Digestibility Reduction• Reallocation of Resources

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Bioactive Specialized Compounds• Alkaloids• Benzoxazinoides• Cyanogenic Glucosides• Glucosinolates• Phenolics• Terpenoids

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Examples of plant Bioactive Specialized Compounds with insecticidal activity

Ibanez et al., 2012 29

Cont…

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Hypersensitive response

• Plant’s response to herbivore results in the formation of necrotic plant tissue and neoplamal g rowth that isolates the invader from plant

• Plants can cast eggs off their leaves

• When an insect deposits its eggs onto a plant, the plant may respond with g rowth of neoplastic tissue and formation of necrotic t issues that results in detachment of eggs

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Oviposition fluid derived elitor induces neoplasmal growth in response to Bruchids in Peas

Doss et al., 2008

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Reymond et al., 2013

Oviposition by Pieris brassicae causes hypersensitive response on Arabidopsis

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(a) Egg of small cabbage white butterfly, inducing hypersensitive response–like necrosis in Brassica nigra. (b) Egg of Heliothis subflexa inducing neoplastic growth in Physalis angulata leaf.

Hilker and Fatouros, 2014 34

Hypersensitivity response to Colorado Potato Beetle oviposition in potato

Balbyshev and Lorenzen, 1999

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Digestibility Reduction

• Plants produce a number of defense compounds that reduce insect herbivores abil ity to digest the plant derived nutrients

Proteinase Inhibitors -amylase inhibitorsα LectinsChitinases Polyphenol oxidases

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Proteinase Inhibitors

• Different classes of proteinases , (trypsin-l ike, chymotrypsin-l ike, and elastase-l ike proteases) found in the midgut region of the insect digest ive tract , are used by insect herbivores to cleave internal peptide bonds in plant proteins

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Role of Tomato protease inhibitor in Plant Immunity to Insect Herbivores

Yan et al., 2013

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α-Amylase Inhibitors

• The lectin-l ike -amylase inhibitors ( -AI) α αare known to produce in cereal , such Wheat , Barley, Sorghum and Maize

• The activities of these inhibitors are directed against -amylases of insects, used for starch αbreakdown

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Lectins

• Lectins are sugar-binding proteins produced by plants as a defense response

• When lectins come into contact with the glycoproteins l ining the intestinal area of insect herbivores, they are assumed to inhibit the absorption of nutrients

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Quantification of NICTABA accumulation in tobacco leaves after feeding by

different herbivores

Vandenborre et al., 201141

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Chitinases

• Chitin is present in the exoskeleton and peritropic membrane of insects

• Role in defense against herbivore by disrupting the gut peritropic memberane

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Polyphenol oxidase• Polyphenol oxidases (PPOs) are anti-

nutrit ive enzymes

• Catalyze the oxidation of phenolics to quinones, which decrease the nutrit ive value of the wounded plant by crossl inking with the nucleophil ic s ide chains of proteins and free amino acids

• Evidence for PPO involvement in plant defense against insect herbivores includes transcriptional induction of PPO genes by insect attack

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Amino acid deaminases

• Amino acid deaminases are another group of anti-nutrit ional proteins in plant defense against insect herbivores

• These enzymes wil l degrade free amino acids in the insect gut , removing nutrients from the herbivore

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Plant defensive proteases, lectins, amino acid deaminases, and oxidation enzymes

Chen, 200546

Reallocation of Resources

• To protect valuable resources, they might be real located by the plant upon attack

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Allocating nitrogen away from a herbivore

Newingham et al., 2007

Spotted knapweedknapweed moth

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Indirect Defense Response The term “indirect defense” is used when

plants attract , nourish or house other organisms to reduce enemy pressure.

• Herbivore-induced plant volati les • Extrafloral Nectar

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Herbivore-induced plant volatiles

• Herbivore-induced plant volati les (HIPV) can mediate indirect defenses, i .e . , by attracting foraging carnivorous predators and parasitoids that ki ll herbivores

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Herbivore-induced plant volati les (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

Rodrigues et al., 2014

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• Herbivore-induced plant volati les (HIPV) are also involved in the plant communication

• HIPVs will helps in the defense priming in the neighboring plants

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Model of defense priming in plant-herbivoreinteractions

53Frost et al., 2008

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 poll inators, EFN is secreted on leaves and shoots to attract predators and parasitoids

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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,andGrammodes geometrica

Secretion of total solids

Malvaceae Gossypium herbaceum(Cotton)

Spodoptera littoralis EFN volume

Martin, 2015 55

Ant visitation to extrafloral nectaries decreases herbivory and increases fruit set in Chamaecrista debilis

Alves and Claro 201056

Conclusion

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Nature has blessed me with Defense mechanism

THANK YOU

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