1. Plant-fungus interactions can involve gene-for-gene systems where a plant resistance gene recognizes a corresponding avirulence gene in the pathogen. This leads to disease resistance but is not durable as it exerts strong selection pressure for new pathogen races.
2. Horizontal or quantitative resistance involves multiple genes and is more durable but provides incomplete resistance. Vertical or race-specific resistance follows the gene-for-gene model and provides complete resistance but is not durable.
3. Avirulence proteins can directly or indirectly be recognized by plant resistance proteins, triggering plant defenses. Pathogens evolve new variants of avirulence genes to avoid recognition and cause disease.
History
Host pathogen interaction
R gene
Molecular techniques for detection of plant pathogens
Role of molecular techniques in resistance breeding Deployment of R genes and linked markers
Transgenic approaches in plant protection
Conclusion
History
Host pathogen interaction
R gene
Molecular techniques for detection of plant pathogens
Role of molecular techniques in resistance breeding Deployment of R genes and linked markers
Transgenic approaches in plant protection
Conclusion
Plant disease resistance genes: current status and future directions.RonikaThakur
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.
Molecular basis of plant resistance and defense responses to pathogensSenthil Natesan
In response to pathogen attack, plants have evolved sophisticated defense mechanisms to delay or arrest pathogen growth.Unlike animals, plants lack a circulating immune system recognizing microbial pathogens. Plant cells are more autonomous in their defense mechanisms and rely on the innate immune capacity of each cell and systemic signals that disseminate from infection sites (Jones and Dangl, 2006). Plant innate immunity consists of preformed physical and chemical barriers (such as leaf hairs, rigid cell walls, pre-existing antimicrobial compounds) and induced defenses. Should an invading microbe successfully breach the pre-formed barriers, it may be recognized by the plant, resulting in the activation of cellular defense responses that stop or restrict further development of the invader.
Systemic Acquired Resistance (SAR) and it’s Significance in Plant Disease Ma...Ankit Chaudhari
Systemic Acquired Resistance (SAR) is a mechanism of induced defense that confers long-lasting protection against a broad spectrum of microorganisms and pests. Presently disease control is largely based on the use of hazardous chemicals viz., fungicides, bactericides and insecticides for either direct or indirect disease management. The hazardous natures of the products on the environment, human and animal health strongly necessitates the search for new safer means of disease control. SAR have high potential to diminish the use of toxic chemicals in the agriculture and has emerged as an alternative, non-conventional, non-biocidal and eco-friendly approach for plant protection and hence for sustainable agriculture. SAR requires the signal molecule salicylic acid (SA) and is associated with accumulation of pathogenesis-related proteins, which are thought to contribute to resistance.
The concept of gene for gene hypothesis was first developed by Flor in 1956 based on his studies of host pathogen interaction in flax, for rust caused by Melampsora lini. The gene for gene hypothesis states that for each gene controlling resistance in the host, there is corresponding gene controlling pathogenicity in the pathogen. The resistance of host is governed by dominant genes and virulence of pathogen by recessive genes. The genotype of host and pathogen determine the disease reaction. When genes in host and pathogen match for all loci, then only the host will show susceptible reaction. If some gene loci remain unmatched, the host will show resistant reaction. Now gene – for –gene relationship has been reported in several other crops like potato, sorghum, wheat, etc. The gene for gene hypothesis is also known as “Flor Hypothesis.”
Gene silencing techniques for crop improvementJhilickBanerjee
Gene silencing is a technique that aims to reduce or eliminate the production of a protein from its corresponding gene. Gene silencing is the regulation of gene expression in a cell.
Gene silencing can occur during either transcription or translation.
Gene silencing is often considered as “Gene knockdown’ i.e their expression is reduced. In contrast , when genes are knocked out they are completely erased from the organism’s genome and thus have no expression.
Methods used to silence genes include RNAi, CRISPR or siRNA, these reduce the expression of the gene by 70% but do not completely eliminate it.
Plant disease resistance genes: current status and future directions.RonikaThakur
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.
Molecular basis of plant resistance and defense responses to pathogensSenthil Natesan
In response to pathogen attack, plants have evolved sophisticated defense mechanisms to delay or arrest pathogen growth.Unlike animals, plants lack a circulating immune system recognizing microbial pathogens. Plant cells are more autonomous in their defense mechanisms and rely on the innate immune capacity of each cell and systemic signals that disseminate from infection sites (Jones and Dangl, 2006). Plant innate immunity consists of preformed physical and chemical barriers (such as leaf hairs, rigid cell walls, pre-existing antimicrobial compounds) and induced defenses. Should an invading microbe successfully breach the pre-formed barriers, it may be recognized by the plant, resulting in the activation of cellular defense responses that stop or restrict further development of the invader.
Systemic Acquired Resistance (SAR) and it’s Significance in Plant Disease Ma...Ankit Chaudhari
Systemic Acquired Resistance (SAR) is a mechanism of induced defense that confers long-lasting protection against a broad spectrum of microorganisms and pests. Presently disease control is largely based on the use of hazardous chemicals viz., fungicides, bactericides and insecticides for either direct or indirect disease management. The hazardous natures of the products on the environment, human and animal health strongly necessitates the search for new safer means of disease control. SAR have high potential to diminish the use of toxic chemicals in the agriculture and has emerged as an alternative, non-conventional, non-biocidal and eco-friendly approach for plant protection and hence for sustainable agriculture. SAR requires the signal molecule salicylic acid (SA) and is associated with accumulation of pathogenesis-related proteins, which are thought to contribute to resistance.
The concept of gene for gene hypothesis was first developed by Flor in 1956 based on his studies of host pathogen interaction in flax, for rust caused by Melampsora lini. The gene for gene hypothesis states that for each gene controlling resistance in the host, there is corresponding gene controlling pathogenicity in the pathogen. The resistance of host is governed by dominant genes and virulence of pathogen by recessive genes. The genotype of host and pathogen determine the disease reaction. When genes in host and pathogen match for all loci, then only the host will show susceptible reaction. If some gene loci remain unmatched, the host will show resistant reaction. Now gene – for –gene relationship has been reported in several other crops like potato, sorghum, wheat, etc. The gene for gene hypothesis is also known as “Flor Hypothesis.”
Gene silencing techniques for crop improvementJhilickBanerjee
Gene silencing is a technique that aims to reduce or eliminate the production of a protein from its corresponding gene. Gene silencing is the regulation of gene expression in a cell.
Gene silencing can occur during either transcription or translation.
Gene silencing is often considered as “Gene knockdown’ i.e their expression is reduced. In contrast , when genes are knocked out they are completely erased from the organism’s genome and thus have no expression.
Methods used to silence genes include RNAi, CRISPR or siRNA, these reduce the expression of the gene by 70% but do not completely eliminate it.
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The Indian economy is classified into different sectors to simplify the analysis and understanding of economic activities. For Class 10, it's essential to grasp the sectors of the Indian economy, understand their characteristics, and recognize their importance. This guide will provide detailed notes on the Sectors of the Indian Economy Class 10, using specific long-tail keywords to enhance comprehension.
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The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
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Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
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1. MOLECULAR CHARACTERIZATION OF GENE FOR GENE
SYSTEMS IN PLANT- FUNGUS INTERACTION AND THE
APPLICATIONS OF AVIRULENCE GENES IN CONTROL OF
PLANT PATHOGENS
1
2. NON HOST RESISTANCE :
• Apple trees and tomato pathogens
• Powdery mildew on wheat (Blumeria graminis f. sp. tritici)
and barley
Disease is exception rather than rule
HORIZONTAL RESISTANCE :
• General resistance, quantitative resistance
• Incomplete resistance but durable
2
3. VERTICAL RESISTANCE :
• Race specific , qualitative resistance, differential resistance
• Complete resistance, not durable – high selection presssure
• Follow gene for gene system
3
PATHOGEN
RACE
PATHOGEN RACE
PLANT VARIETY 1 2 PLANT VARIETY 1 2 3 4
A _ + A _ + + +
B + _ B + _ _ +
C _ + _ +
D + _ + _
4. Reaction of plants to attacks by various pathogens in relation to resistance of
the plant
4
Agrios (2005)
5. Each gene that confers avirulence (Avr) to the pathogen there is a
corresponding gene in the host that confers resistance (R) to the host
and vice versa – H.H.Flor (1946)
5
RESISTANT OR SUSCEPTIBILITY GENES IN THE
PLANT
VIRULENCE OR AVIRULENCE
GENE IN PATHOGEN
R (resistant)
dominant
r ( susceptibility)
recessive
A (avirulent) dominant AR (-) Ar (+)
a ( virulent) recessive Ar (+) ar (+)
6. 6
RESISTANCE (R) OR SUSCEPTIBILITY ( r) GENES
IN THE PLANT
R1 R2 R1 r2 r1 R2 r1 r2
VIRULENCE (a) OR
AVIRULENCE (A)
GENES IN THE
PATHOGEN
A1 A2 - - - +
A1 a2 - - + +
a1 A2 - + - +
a1 a2 + + + +
10. Hydrophilic- lacking stretches of hydrophobic amino acids - enable
them to be anchored in cell membranes
May produced and localized in pathogen cytoplasm or secreted
through membrane pores
If secreted externally – directly acts as elicitors
If localized in cytoplasm of pathogen - acts indirectly as enzyme to
produce elicitor molecules
Acting as avirulence factors in elicitor-receptor model (plant
defense)
10
11. Contribution towards the virulence of pathogen. eg. AvrBs2 gene of
X. campestris pv. Vesicatoria
Avr proteins interact with specific plant proteins (virulence target) -
enhances availability of nutrients to pathogen .
Most R proteins contain amino acid leucine rich domain (LRR-
leucine rich repeats),
Depending on R protein LRR reside : cytoplasmic LRRs or
extracytoplasmic LRRs.
Leucine-rich repeats (LRR) region of R-genes is involved in
recognizing pathogens
11
12. MAJOR CLASSES OF R PROTEINS
S. NO MAJOR R-GENE CLASSES EXAMPLE
1 NBS-LRR-TIR N, L6, RPP5
2 NBS-LRR-CC I2, RPS2, RPM1
3 LRR-TrD Cf-9, Cf-4, Cf-2
4 LRR-TrD-Kinase Xa21
5 TrD-CC RPW8
6 TIR-NBS-LRR-NLS- WRKY RRS1R
7 LRR-TrD-PEST-ECS Ve1, Ve2
8 Enzymatic R-genes Pto, Rpg1
LRR - Leucine rich repeats; NBS - Nucleotide-binding site; TIR -Toll/Interleukin-
1- receptors; CC - Coiled coil; TrD –Transmembrane domain; PEST -Amino acid
domain; ECS - Endocytosis cell signaling domain; NLS - Nuclear localization
signal; WRKY -Amino acid domain; HC toxin reductase - Helminthosporium
carbonum toxin reductase enzyme.
12
Gururani et.al.,2012
15. Plant proteins belonging to
the nucleotide-binding site–
leucine-rich repeat (NBS-
LRR) family are used for
pathogen detection.
(R-PROTEIN)
Harmful organism
Recognition by
resistance protein
Signal to cell
nucleus
Genetic
material
Defense
Response Defense protein
(R-PROTEIN)
Outside
plant
cell
Inside
plant
cell
Diagram of a plant disease resistance protein in action. A portion of the protein
(MAROON) lies outside the cell and specifically recognises the harmful organism.
The remaining portion of the protein (RED) resides inside the cell and
communicates a signal to the plant’s genetic material, which in turn stimulates a
defense response against the invading organism.
(R-GENE)
15
16. • INDIRECT PERCEPTION OF AVR PROTEINS:
Protease dependent defense elicitation model
The co-receptor model
The guard hypothesis
The decoy hypothesis
Bait and Switch model
•DIRECT PERCEPTION OF AVR PROTEINS :
Elicitor- receptor model
16
17. Albersheim and Anderson Prouty, 1975 proposed this model.
Avirulence (Avr) gene of a pathogen encodes an elicitor (Avr) protein
that is recognized by a receptor protein encoded by the matching
resistance (R) gene of the host plant.
eg. Pi-ta R gene from rice and AvrPi-ta from Magnaporthe grisea
ELICITOR– RECEPTOR MODEL
17
Staskawicz et.al.,1995
18. PROTEASE DEPENDENT DEFENSE ELICITATION
MODEL
Kruger et al., 2002 proposed this model.
eg.Tomato leaf mold –Cladosporium fulvum interaction.
Rcr3 required for Cf-2 mediated resistance towards C.fulvum
strains carrying Avr2, encodes a tomato cysteine endoprotease.
Rcr3 might process Avr2 to generate a mature ligand, or Rcr3
might degrade Avr2 - releasing active elicitor peptides that
interact with the extracellular LRR of Cf2.
18
20. THE CO-RECEPTOR MODEL
Jones and Jones,1996 proposed this model.
RPS5 an Arabidopsis NB-LRR protein localized to a membrane
fraction - activated by the AvrPphB cysteine protease effector from P.
syringae.
AvrPphB is cleaved, acylated and delivered to the host plasma
membrane. Activated AvrPphB cleaves the Arabidopsis PBS1 serine-
threonine protein kinase, leading to RPS5 activation.
20
22. THE GUARD HYPOTHESIS
Van-der-biezen and Jones, 1998 proposed this model.
Interaction between guardee and Avr is recognized by the R
protein
eg. AvrPto of Pseudomonas syringae and Pto gene of tomato,
Prf gene act as guardee.
Evolutionary unstable situation
R protein is absent -evolution of the guardee to avoid binding
R protein is present - selection will favor binding
22
24. Van der Hoorn and Kamoun, 2008 proposed this model.
Host protein termed as “decoy” - specializes in perception of the
effector by the R protein
Not contributing pathogen fitness in the absence of its cognate R
protein.
Effector target monitored by the R protein is a decoy that mimics
the operative effector target
e.g. AvrPto and AvrBs3 - some host targets of effectors act as
decoys to detect pathogen effectors via R proteins
DECOY HYPOTHESIS
24
26. Peter Moffett , proposed this model in 2002.
The NB-LRR protein - primed (signaling competent) but
autoinhibited (restrained from signaling) state.
Functional nucleotide binding pocket and multiple intramolecular
interactions - fine-tuned balance between the LRR and ARC2.
Avr protein is brought into the NB-LRR system via the bait protein
- direct binding or alteration to bait.
Conformational changes within the nucleotide binding pocket-
allow signaling motif - downstream signaling components.
Subsequent to signaling, intramolecular interactions within the NB-
LRR protein dissociated.
BAIT AND SWITCH MODEL
26
44. FLAX RUST –
All the virulent rust strains retain intact copies of the Avr genes
(AvrL567) but have altered their sequences
Host R genes imposed selection for new variants to escape recognition.
44
Jones & Dangl (2006)
47. Functional genomic tools to disease resistance - interactions between
defense signaling and other plant processes.
Structural basis of recognition will enable us - design R proteins that
recognize essential virulence factors
New transgenic resistant plants by exploiting both avirulence genes
and resistance genes in molecular resistance breeding
Using avirulence gene products / race-specific elicitors - events in
signal transduction pathways can be studied.
47