Flow of

WEL COME

VARSHA GAYATONDEPALB 2235

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SEMINARON

Genetics of Host Plant Disease Resistance

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Contents

1. Terminologies

2. Disease and Importance of Host plant Resistance.

3. Scientists contribution.

4. Types of Genetics Resistance.

5. Host Pathogen interaction.

6. R genes application in plant breeding.

7. Resistance Breeding

8. Conclusion.

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Terminologies

• Elicitor: The signaling molecules.• Effector: Typical proteins that are delivered outside the microbe.• Pathotype: population of a parasite species in which all

individuals have a pathogenicity or parasitic ability in common. • Biotype: progeny developed by variant having similar heredity.• PRR-Transmembrane Protein Recognition Receptors.• PAMP/DAMP:Pathogen Associated Molecular Patterns.• PTI: PAMP-Triggered Immunity• ETI-Effector Triggered Immunity.• NBS-LRR-Nucleotide Binding Luicine rich Repeat regions.• MAPK:Mitogen Activated Protein Kinase

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Agrios, G.N. 1998

Different Pathogens Causing diseases

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Biffin(1901) Demonstrated Genetic basis of Disease resistance.

Studies conducted on Wheat rust.

Obtained 3:1 Mendelian ratio by crossing Rivet x Red king.

“Resistance is Heritable”

Resistance and susceptibility are independent of other plant characters.

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H H Flor(1952) Genetic factors of both plant and pathogen are

required for the successful defence response of plant.

Wheeler rule-1: Incompatible Reaction Found in Biotrophs. Avr-R recognises each other and their speificity

and interaction gives resistence to host.

Wheeler rule-2: Compatible reaction Avr-r produce specific compounds ,which

interact each other and produce the susceptible response.

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Rules of Flor’s Hypothesis(1952)

IncompatibilityResistance Gene Compatibility

Given by Wheeler(1975)

Virulence gene

Avr1 avr1 Avr1 avr1

R1

r1

R

S

S

SR

R R

s

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Infected HR

Results From Flor’s Crosses• 25 resistance alleles distributed across 5 loci were identified • Locus # Alleles K1 L11 M6 N3 P4• For every resistance allele found in the plant, a corresponding  virulence allele was found in the pathogen.• There is a gene‐for‐gene interaction between host and parasite.• L and M loci cloned and sequenced in 1995. •  13 different alleles  characterized at

L locus gave important insights into functions of R‐genes.10

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BOOM YEARS

BUST YEARS

Each race specific r genes has only a limited life span

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Priestley(1970)

Types of Genetic Resistance• Qualitative Resistance

• Distinct classes of resistance and susceptible plants

• Controlled by one or a few genes

• Also called “Vertical” resistance

• Quantitative Resistance• Continuous variation among

genotypes• Many loci• Also called “Horizontal”

resistance14

Genetics of ResistanceMechanisms of resistance:

1.Disease escape

2.Disease endurance.

3.True resistance

Classification Based on:

1.Number of Genes

2.Biotype reaction

3.Population/Line concept

4.Evolutionary concept.

5.Specificity.

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Defense mechanism in plants

Perception

Signaling

Response

Plant –Pathogen Interaction

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How pathogen and host recognize each other.?

The gene-for-gene hypothesis between host and pathogen for triggering race-specific resistance.

I- incompatible ,C- compatible 18

Elicitor – receptor model

Perception

Perception of elicitor signals/ receptors for elicitor signals in plant cell membrane

• Salicylic acid, Jasmonic acid and Ethylene

• Protein kinase as receptor sites

• LRR-type receptors

• Lectins as receptors

• Resistance gene product as receptors 19

•  Molecules that relay signals from receptors on the cell surface to target molecules.

Earl Wilbur Sutherland, discovered secondary messengers, won the 1971 Nobel Prize in Physiology or Medicine.

Functions:• They greatly amplify the strength of the signal.

• Component of signal transduction cascades.• Secondary messengers.• Calcium ion• Anion channels in signal transduction • Phosphorylation and Phospholipids signaling system • Mitogen-activated protein kinase signaling cascade

Secondary messengers(signaling)

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(Hamel et al., 2012)ACS- 1-aminocyclopropane-1-carboxylic acid synthase, 22

Role of Mitogen-activated protein kinase cascade

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Response

• Resistance

• Susceptible

Differential response of plant to pathogens

(Yan Zhang et al., 2013)24

(Nurnberger et al.,2006)25

Mechanisms of plant defense• Hypersensitive response

• Production of reactive oxygen species

• Production of antimicrobial metabolites

• Defense signal transduction

• Synthesis of enzymes (e.g. - chitinases, glucanases)

(Thirupathi et al., 2011)26

Role of ROS

• Alkalization and cytoplasmic acidification

• Reactive oxygen species

• Nitric oxide in signal transduction

• Salicylic acid signaling system

• Jasmonate signaling pathway

• Ethylene dependent signaling pathway

• Fatty acids as systemic signal molecules 27

Signaling systems

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Resistant Genes(R Genes)

Application in Plant Breeding.

Schematic representation of domains found in plant LRR R proteins. Domains are not drawn to scale. TIR Toll/interleukin-1 receptor, CC coiled coil, NB nucleotide binding, ARC1/2 APAF1, R protein and CED4, LRR leucine rich repeat, SD solanaceous domain, BED BEAF/DREAF zinc finger domain, TM transmembrane, Kin kinase, WRKY WRKY transcription factor

(Wladimir et al., 2008)

Domain Function Gene LRR Protein-protein interaction.

Its major determinants of recognition specificity Pi-ta, Cf 4,9,5

NBS To bind ATP r GTP.Race specificity functions of R gene

L6

TIR Race specificity functions of R gene L6

CC Involved in recognition of avr gene product RPW 8

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Sources of Resistance• Primary Gene Pool• Other breeding programs• Landraces• Germplasm collections (GRIN)

• Wild Relatives• Tomato: Lycopersicon genus• Wheat: Agropyron genus • Aegilops tauschii, Triticum monococum

• Mutant Transformations: powdery mildew in Barley

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Identification of R genesCandidate gene identification by readily designed PCR primers.

R gene molecular isolation2 methods:

1.Map based identification.

2.Transposon tagging

Map based isolation of R genes

Genetic marker 1

Genetic marker 2R gene

M3 M4

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Types of problems encountered

- A ‘LONGER WALK’ than expected - lack of recombination- An unknown ‘HOLE IN THE BAC CLONE’ RPM1- Which gene is it ? PTO

Disease reaction R R S S

5. Transform a susceptible genotypewith a single cosmid clone

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Map based isolation of R genes

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Wang and Yano

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Map Based Cloning of Pi9Include recent R gene cloning paper in r

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Cloned rice resistant genesInclude bullet points of Whole presentationThen conclude

Tomato Cf-9 : Avr9

Transposon inactivationof R gene

30 C 22 C

TMV

nn

NN

with genetic selection

Tobacco N gene

Transposon Tagging of R Genes

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R gene expression

Very low and constitutive

Occasionally low level induction following infectionbut only in the vicinity of the pathogen

Rarely expressed only in resistant genotype - Rice Xa27 – Xanthomonas oryzae pv. oryzae

Susceptible alleles 10 bp and a 25 bp insertion in the promoter.

(Gu et al, (2005) Science 435: 1122-1125) 40

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How do R proteins function ?

Three examples

Direct pathogen molecule recognition

Indirect pathogen molecule recognition

AvrPtoor AvrPtoB

ptoPto

HRLess pathogen

proliferation

AvrPto and AvrPtoBeffectors bind to

unknown host target

Prf

Enhanced pathogenvirulence

Susceptiblehost

Resistant Pto host

Adapted from Jones and Dangl (2006) Nature

Pseudomonas syringae

Direct recognition Tomato Pto - AvrPto

cell wall

plasmamembrane

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AvrRpm1or AvrB

HRLess pathogen

proliferation

AvrRpm1effector bind to host target RIN4and other targets

RPM1

Enhanced pathogenvirulence

Susceptiblehost

Resistant RPM1 host

Adapted for Jones and Dangl (2006) Nature

RIN4 P

PP

NDR1

No RPM1

RIN4 P

PP

NDR1

Pseudomonas syringae

Indirect recognition Arabidopsis RPM1- AvrRpm1

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Virulence Target

AvrSusceptible responseto favour pathogen growth and development

B. INCOMPATIBLE INTERACTION

Virulence TargetAvr R3

Resistance by guarding

AvrB/ RIN4 RPM1AvrRpm1

Avr2 Rcr3 Cf-2

R Protiens Guard The Virulence Target

Resistance response

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Approaches for Host Plant Resistant Breeding

Individual Major Genes.

Breeding for Quantitative traits.

Multilines.

Marker assisted back crossing.

Pyramiding.

Breeding for Specific Resistance

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Biotechnological approach

Marker assisted plants breedingDifferent markers and application in disease resistance Achievements

Tissue culture methodsSomaclonal variation Somatic hybridization

Genetic engineering (Transgenics)

Meristem – Tip culture (for virus free planting material)

General breeding approaches-Introduction, Selection, Hybridization Backcross ,Induced mutagenesis

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Host species Pathogen Resistance gene Marker Reference

Rice Pyricularia oryzae Pi-2(t), Pi-4 (t) Pi-10 (t)

RFLPRAPD

Yu et al, 1991Naqvi et al, 1995

  Xanthomonas oryzae Xa2I Xa3, Xa4,  

RAPDRFLP

Zhang et al, 1994Yoshimura et al, 1995

  Orseolia oryzae Gm2, Gm4t RAPD Mohan et al. 1994

Wheat Puccinia recondite Lr9, Lr24 RFLP an RAPD

Schachermayr et al. 1994, 1995

  Erysiphe graminis Pm1, Pm2, Pm3 RFLP Hartl et al, 1995

  Hessian fly H21 RAPD Seo et al., 1997

Maize Leaf blight Rhm RFLP Zaitlin et al. 1993

Barley Stm rust Rpg 1 RFLP Kilian et al 1994

  Barley yellow mosaic ym4 RFLP Graner an Bauer, 1993

  Rhyncosporium - RFLP Graner and Tkauz, 1996

Brassica napus Leptosphaeria maculans - RFLP Ferreira et al, 1995

Pea Erysiphe polygoni er RFLP Dirlewanger et al, 1994

Mungbean Bruchid Callosobruchus - RFLP Young et al, 1992

Tomato Fusarium oxysporum I2 RFLP Sarfatti et al. 1991

  Cladosporium fulvum Cf2/Cf5 RFLP Dickinson et al, 1993

Potato Cyst nematode (Globodera Rostochiensis)

HI RFLP Pineda et al, 1993

Some examples of molecular markers associated with resistance traits in crop plants (MAS)

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Resistant genes incorporated against specific pathogens through MAB

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QTL Pyramyding

Breadth of Resistance-Promoter Induced

Breadth of Resistance-NPR-1

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