FIG. 1. L6 gene DNA probes detect RFLP markers linked to the L and M loci. (A) Map of the L6 region and location of DNA probes. Thelocation of the transcribed region and the two 480-bp direct repeats are indicated with arrows. H, HindIII; Bg, Bgl II; RI, EcoRI; B, BamHI; S,Sph I; X, Xba I. (B) RFLP pattern detected in the parents, Forge (F) and Hoshangabad (H), and some of the 52 test-cross progeny using XbaI-digested DNA and probe LU-2. The presence of the L6 and M resistance genes was determined by inoculation with the appropriate rust strains.The absence of these genes is indicated by a blank square. The positions of the DNA fragments that provide the four RFLP alleles LU2-2A/B (Mlinked) and LU-2-1A/B (L linked) are indicated. In each case, the A allele is derived from Forge and the B allele is from Hoshangabad.by probe
After evaluation of numerous physiological, biochemical and genetic experiments,
Genetically defined relationships be-tween salicylic acid (SA)-dependent andethylene–jasmonic acid (ET–JA)-depend-ent defense responses in Arabidopsis.The SA-dependent response is deployedagainst a biotrophic pathogen that ob-tains nutrients from living cells, whereasthe ET–JA response is activated bynecrotrophic pathogens that kill plant tis-sue. Resistance to necrotrophs (but notthe biotroph) is compromised in anArabidopsis mutant (coi1) that does notrespond to JA. Expression of a transgene(NahG) that degrades SA compromisesresistance to the biotroph but not thenecrotrophs. These pathways appear tobe mutually inhibitory.
RLK-receptor like protien kinase.pdf1.2 gene-a pathogen related gene act as a defensin in arabidopsis.wound related kinase 1.PRR_pattern recognition receptorsTtss-type 3 secretion system
Fig. 2 Physical map of chromosome 7D in wheat showing markersthat are ﬂanking Lr34/Yr18 and contained within the deletion bin7DS-4 which consists of approximately 39% of the short arm ofchromosome 7D (on the left). The genetic map of the Lr34/Yr18region shows microsatellite markers that ﬂank the resistance genes.Numbers on the left hand side denote genetic distance incentiMorgans. Resistance to powdery mildew (Pm) cosegregatedwith leaf rust and stripe rust resistance. A–D denote conﬁdenceintervals for QTLs for rust resistance previously assigned to thisregion: A QTL for leaf rust and stripe rust identiﬁed by Suenagaet al. (2003), B QTL for leaf rust QLr.str-7DS described bySchnurbusch et al. (2004), C QTL for leaf rust QLrP.sfr-7DSidentiﬁed by Schnurbusch et al. (2004), D QTL for stripe rustQYr.sgi-7D identiﬁed by Ramburan et al. (2004)
Identification in pib gene isolation.
Aa sequence is-nbslrr.Duplicated kinase 1a 2a 3a motifs,8cysten residues are clustered in the middle of lrr.
Contigs –gel readings. Pi9 was introgressed from wild rice Oryzaminuta to cultivated rice line 75-1-127. Tightly linked markers (pBV14, pB8 and pBA14) wereidentified using RAPD and bulk segregant analysis. pB8 was used to screen both BAC and cDNA libraries. A contig was constructed usingpositive BAC clones. Candidate genes, identified from the sequenced contig, were used for transformation. Transgenic lines were evaluatedfor resistance to rice blast.
Pto-psuedomons syringe pv.tomato
Prr-transmembrain pattern recognition receptorsRlps –arabidopsis receptor like proteinsRIN4-A 211 AMINO ACID ACYLATEd,and plasma membrane associate protien,is type 3 effector gaurded by nbs-lrr.AvrRpm1 or avrb are the 2 unrelated protiens
Fig. 3. Strategy for engineering broad-spectrum resistance by induction of Avr/Rtransgene combinations. A pathogen Avr gene is expressed in plant cells as atransgene, under the control of a plant promoter that is induced by a range ofpathogens. A corresponding R gene (either endogenous or a transgene) is alsoexpressed. Upon pathogen attack, the pathogen-responsive promoter is activated,the Avr gene is expressed, and the Avr protein interacts with the R protein toinduce the HR and other defense responses. Note that this system can be activatedby any pathogen (or spurious stimulus) that is capable of activating the promoterof the Avr gene.
Fig. 4. Regulation of defense gene expression by NPR1. NPR1 has an importantrole in ‘local’ resistance triggered by some R genes, as well as two types of sys-temic resistance: Systemic acquired resistance (SAR), which is induced by nectro-tizing pathogens on foliar tissue and which acts through salicylic acid (SA); andinduced systemic resistance (ISR), which is induced by soil-dwelling bacteria andacts through jasmonic acid (JA) and ethylene (ET) . These cascades trigger anas-yet unknown posttranslational modiﬁcation of NPR1 (depicted by a red star).NPR1 then translocates from the cytoplasm to the nucleus . Once inside thenucleus, NPR1 interacts with TGA transcription factors, and perhaps other pro-teins, to regulate transcription of defense-associated genes [54,55].
Varu gaitonde genetics of host plant disease resistance
Genetics of Host
Disease and Importance of Host plant Resistance.
Types of Genetics Resistance.
Host Pathogen interaction.
R genes application in plant breeding.
• 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
Different Pathogens Causing diseases
Agrios, G.N. 1998
Demonstrated Genetic basis of
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.
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
Wheeler rule-2: Compatible reaction
Avr-r produce specific compounds ,which
each other and produce the
Rules of Flor’s Hypothesis(1952)
Given by Wheeler(1975)
Results From Flor’s Crosses
• 25 resistance alleles distributed across 5 loci were identified
• Locus # Alleles
• 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
race specific r genes has only a
limited life span
Types of Genetic Resistance
• Distinct classes of resistance
and susceptible plants
• Controlled by one or a few
• Also called “Vertical”
• Continuous variation among
• Many loci
• Also called “Horizontal”
Genetics of Resistance
Mechanisms of resistance:
Classification Based on:
1.Number of Genes
How pathogen and host recognize each other.?
The gene-for-gene hypothesis between host and pathogen for
triggering race-specific resistance.
Elicitor – receptor model
I- incompatible ,C- compatible
Perception of elicitor signals/ receptors
for elicitor signals in plant cell
• Salicylic acid, Jasmonic acid
• Protein kinase as receptor sites
• LRR-type receptors
• Lectins as receptors
• Resistance gene product as
Molecules that relay signals from receptors on the cell surface to
Earl Wilbur Sutherland, discovered secondary messengers, won the
1971 Nobel Prize in Physiology or Medicine.
• 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
Role of Mitogen-activated protein kinase cascade
ACS- 1-aminocyclopropane-1-carboxylic acid synthase,
et al., 2012)
Differential response of plant to pathogens
(Yan Zhang et al., 2013)
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)
(Nurnberger et al.,2006)
• 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
Resistant Genes(R Genes)
Application in Plant Breeding.
Its major determinants of recognition specificity
Pi-ta, Cf 4,9,5
To bind ATP r GTP.
Race specificity functions of R gene
Race specificity functions of R gene
Involved in recognition of avr gene product
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)
Sources of Resistance
• Primary Gene Pool
Other breeding programs
Germplasm collections (GRIN)
• Wild Relatives
Tomato: Lycopersicon genus
Wheat: Agropyron genus
Aegilops tauschii, Triticum monococum
• Mutant Transformations: powdery mildew in Barley
Identification of R genes
Candidate gene identification by readily designed
R gene molecular isolation
1.Map based identification.
Map based isolation of R genes
Map based isolation of R genes
5. Transform a susceptible genotype
with a single cosmid clone
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
Map Based Cloning of Pi9
Include recent R gene cloning paper in r
Cloned rice resistant genes
Include bullet points of Whole presentation
Transposon Tagging of R Genes
with genetic selection
Tomato Cf-9 : Avr9
Tobacco N gene
of R gene
R gene expression
Very low and constitutive
Occasionally low level induction following infection
but 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
(Gu et al, (2005) Science 435: 1122-1125)
How do R proteins function ?
Direct pathogen molecule recognition
Indirect pathogen molecule recognition
Direct recognition Tomato Pto - AvrPto
AvrPto and AvrPtoB
effectors bind to
unknown host target
Adapted from Jones and Dangl (2006)
Indirect recognition Arabidopsis RPM1- AvrRpm1
effector bind to
host target RIN4
and other targets
Adapted for Jones and Dangl (2006) Nature
R Protiens Guard The Virulence Target
to favour pathogen
growth and development
B. INCOMPATIBLE INTERACTION
Resistance by guarding
Approaches for Host Plant
Breeding for Specific Resistance
Individual Major Genes.
Breeding for Quantitative traits.
Marker assisted back crossing.