Agriculture plays a key role to ensure the food security. But plant diseases hinder the crop production by reducing yield to much extent. To overcome this problem it is crucial to understand plant disease resistance genes which prevent growth of plant pathogens thereby reducing the yield loss.

1. Plant Disease Resistance Genes-
Current Status and Future
Directions
Presented by: Ronika (A-2020-40-017)
(Ph.D. Genetics and Plant Breeding)
Credit Seminar: Pl Path-591

2. *7.90 Billions Population (world)
*1.39 Billions Population (India)
Global trade
Plant pests and
diseases are
responsible for
losses of 20 to
40% of global
food production.
Climate change Abbas et al. 2021
Plant Diseases
• Threat to food security
• Reduces crop quality
Food Security
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3. 3
Introduction
Resistance gene
Classification of R gene
Avirulence gene
Plant-pathogen interactions
Conclusion

4. What is a Disease
Malfunctioning process that is caused
by continuous irritation which
results in some suffering producing
symptoms.
(Congenial)
(Susceptibility)
(Virulence)
Plants
Exposed to
many
microbes
Only few lead
to disease
development
Why?
4
Host-Pathogen
Interaction

5. Gene for Gene Hypothesis
Pathogen
genotype
Host genotype
R1 r1
Avr1
- +
avr1
+ +
- = Incompatible reaction
+ = Compatible reaction
“for each gene
conditioning
rust reaction
in the host
there is a
specific gene
conditioning
pathogenicity
in the
parasite”- Dr.
H.H. Flor
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6. Gururani et al. 2012
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7. 7
Agrios, 2007
Interaction between two ‘R’ and ‘Avr’
genes
PATHOG
EN/HOS
T
R1R2 R1r2 r1R2 r1r2
A1A2
- - - +
A1a2
- - + +
a1A2
+ + - +
a1a2
+ + + +

8. Steps in Host-Pathogen Interaction
PERCEPTION SIGNALING RESPONSE
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9. 1). Host-Pathogen Recognition
• Elicitor Receptor Model (Albersheim et al. 1981)
• Dimer Model (Ellingboe 1982)
• Ion Channel Model (Gabriel 1984)
• Suppressor Receptor Model (Bushnell & Rowell 1981 and Heath
1982)
Direct Interaction
• Guard Hypothesis
Indirect Interaction
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10. 2). Signaling
Perception and conveyance of information from outside the
cell to the nucleus or other sites within the cell, leading to a
cellular response.
Signal transduction occurs in response to a signal and
consists of a series of post-translational modifications
that regulate the activity of proteins.
G-Proteins, Calcium ions, Mitogen activated protein
Kinases, Reactive Oxygen Species (H2O2), Nitric Oxide,
Salicylic Acid, Jasmonic Acid, Ethylene.
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11. Perception
Transduction
Response
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12. 3). RESPONSE
HYPERSENSITIVE
RESPONSE (HR)
SYSTEMIC
ACQUIRED
RESISTANCE (SAR)
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13. 13

14. Plant Defense System
Basal
• 1st line of defense
• Constituent of both non host and host resistance
• Elicitor: cell wall derivatives
• PAMPs: lipopolysaccharides, chitins, glucans, flagilins
• Non pathogen & pathogen can trigger
• Adapted microbes expresses effector protein to
suppress defenses of plants
R-gene
mediated
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• Effectors encoded by Avr genes
• Race specific
• Associated with HR response
• Signal transduction

15. Plant Immune system
Jones and Dangl 2006 15

16. 16

17. Resistance genes
R genes convey plant disease
resistance against pathogens
by producing R proteins.
First cloned R-gene was Hm1 from
MAIZE while First Avr specific R-gene
cloned was Pto from tomato.
First cloned Avr gene was Cf9
from Cladosporium fulvum
Signaling of plant stress
hormone
Generation of reactive
oxygen species
Ethylene biosynthesis
Phytoalexin synthesis
Cell wall strengthening by
deposition of callose and HR
response
Functions
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18. Examples of R-GENES
PLANT R-Gene Name PATHOGEN
Pepper
Rice
Bs2
Pi-ta
Xanthomonas campestris
Magnaporthe grisea
Flax
Arabidopsis
L
RPS4
Melampsora lini
Phytopthora parasitica
Tomato Cf2
Cf4
Cladosporium fulvum
Rice Xa21 Xanthomonas oryzae
Maize Hm1 Cochliobolus carbonum
Agrios, 2007

19. R genes
Reduction of
pathogen growth
Minimal damage to
host plant
Zero input of
pesticides
Environment
friendly
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Most of R genes are dominant but recessive genes
has also been reported; mlo in barley, rice xa5 and
xa13 etc.
R gene broad range host resistance Mi-1 gene in
tomato confers resistance to root-knot nematodes,
potato aphid, whitefly, viruses, bacteria and fungi.

20. R-GENE STRUCTURE
R-genes consist of different domains. The great majority are
intracellular NBS-LRR. The few members possess extracellular LRR-
domain.
20
Nibblers

21. LRR (Leucine Rich Repeat) DOMAIN
• LRR consists of 2-45 motifs of 20-30 amino acid in length that
generally folds into an arc or horseshoe structure. Each motif contain
leucine residues at regular interval. It is involved in protein-protein
interactions.
• Role for recognition specificity
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22. NBS (Nucleotide Binding Site) DOMAIN
NBS is present in several protein families including ATPases and
G-proteins and may affect R-protein function through
nucleotide binding or hydrolysis. It may be involved in
regulating programmed cell death.
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23. CC (Coiled Coil) DOMAIN
The CC-structure is repeated heptads sequence with interspersed
hydrophobic amino acid residues. It consists of two alpha or more
alpha helices that interact to form a supercoil. This domain may be
involved in downstream signalling.
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24. STK (Serine Threonine Kinase) DOMAIN
Kinases are heterodimer with catalytic and regulatory site. The
most common protein kinases present in plants are CDKs and
MAP Kinases.
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25. LZ (Leucine Zippers) DOMAIN
These work like molecular switches binding to DNA and switching on or
silencing the genes ability to synthesize a particular protein.
TIR (Toll Interleukin Receptor) DOMAIN
The TIR domain is implicated in signalling by its similarity to the
cytoplasmic domain of Toll and IL-I R. Play role in pathogen recognition.
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26. Classes
LRR -Leucine rich repeats; NBS-Nucleotide-binding site; TIR-Toll Interleukin-1- receptors; C-C-Coiled coil; TrD-Transmembrane
domain; PEST-Protein degradation domain (Proline-glycine-serine-threonine); ECS- Endocytosis cell signaling domain; NLS-
Nuclear localization signal; WRKY - Amino acid domain; Hm1-Helminthosporium carbonum toxin reductase enzyme 26
Gururani et al. 2012

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30. Model for R protein activation
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31. Gururani et al. 2012
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32. Gururani et al. 2012 32

33. Gururani et al. 2012 33

34. Gururani et al. 2012 34

35. Avirulence Genes
A pathogen gene is called an Avr gene if its expression causes the pathogen to produce
a signal that triggers a strong defense response in a plant with the appropriate R gene.
However, expressing an Avr gene does not stop the pathogen from being virulent
on hosts that lack the corresponding R gene.
Thus, Avr gene are the mild genes of the pathogen which are responsible for
activation of certain defense responses of the host plants.
More than 40 bacterial Avr genes have been cloned and sequenced, primarily from the
genera Pseudomonas and Xanthomonas.
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36. Evolution of genes for virulence, resistance & avirulence
Agrios, 2007 36

37. 37
Variation in R-genes
• Generation of repeated sequences within gene eg. 2 clusters
of Cf 9 gene homologue identified on chromosome 1 of
tomato
• Large duplication (17 kb) in Xa21 multigene family, Pto gene
family has generated alternate recognition capability of
encoded protein
• Reshuffling of existing genes & creation of new, amplify &
reduce number of resistance gene family reported in Cf genes
Gene
duplication&
recombination
• Reconstruction of genome in response to pathogen
infection eg. Hm1 gene-TE (Drone 256bp)- inbred
susceptibility for disease
• Major source of variability in Xa21 gene family- 17 TEs
• Evolution by creating epigenetic variation eg.
Arabidopsis thaliana and RPP resistance gene.
Transposable
elements
Gupta et al. 2012

38. Conclusion
• Most resistance genes exhibit exquisite recognition specificity & new resistance genes can be
created in the laboratory through single point mutations. Cloned resistance and effector
genes can be used in combination to promote acquired resistance to ‘trigger’ HR response.
• R-genes have remarkable property of rapid diversification under selective pressure from the
pathogens and are highly polymorphic having common structural domains. The DNA
rearrangements plays a crucial role in R-gene evolution allowing plants to generate novel
resistance specificities to match the changing virulence pattern of the pathogen.
• Several evolutionary patterns can be inferred from the molecular studies of resistance genes.
• PRGdb (http://prgdb.org) has been developed which provides a comprehensive overview of
the resistance genes currently have information of 112 known and 105692 putative R-genes
present in 237 plant species which confers resistance to 124 different pathogens.
• Functional genomics tools for disease resistance could help us better understand the plant
defense signaling, could reveal novel insights on the interactions between these signaling
pathways and other plant processes.
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39. References
• Abbas U, Khan HM, Faisal M, Ayub I, Shafqat and Tahir T. 2021. Role of
interference RNA (RNAi) in plant disease management. Transactions in Physical
and Biochemical Sciences 1: 57-69
• Agrios GN. 2007. Plant Pathology 5th ed. Academic Press, Inc.: New York. P 125
• Gupta SK, Rai AK, Kanwar SS and Sharma TR. 2012. Comparative analysis of Zinc
Finger proteins involved in plant disease resistance. PLoS ONE 7: e42578
• Gururani MA, Venkatesh J, Upadhyaya CP, Nookaraju A, Pandey SK and Park SW.
2012. Plant disease resistance genes: Current status and future directions.
Physiological and Molecular Plant Pathology 78: 51-65
• Jones JDG and Dangl JL. 2006. The plant immune system. Nature 444: 323-329
• Sharma TR, Das A, Thakur S and Jalali BJ. 2014. Recent understanding on
structure function and evolution of plant disease resistance gene. Proceeding
of the Indian National Science Academy 80: 83-93 39

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