gene for gene system in plant fungus interaction
TRANSCRIPT
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MOLECULAR CHARACTERIZATION OF GENE FOR GENE
SYSTEMS IN PLANT- FUNGUS INTERACTION AND THE
APPLICATIONS OF AVIRULENCE GENES IN CONTROL OF
PLANT PATHOGENS
DOCTORAL SEMINAR-II
VINOD UPADHYAY
ID: 440561
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INTRODUCTION
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
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VERTICAL RESISTANCE :
• Race specific , qualitative resistance, differential resistance
• Complete resistance, not durable – high selection presssure
• Follow gene for gene system
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PATHOGEN RACE
PATHOGEN RACE
PLANT VARIETY 1 2 PLANT VARIETY 1 2 3 4
A _ + A _ + + +
B + _ B + _ _ +
C _ + _ +
D + _ + _
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Reaction of plants to attacks by various pathogens in relation to resistance of the plant
4Agrios (2005)
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GENE FOR GENE HYPOTHESIS
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 (+)
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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 + + + +
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ELICITOR AND RECEPTOR CONCEPT
7Agrios (2005)
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R-AVR GENE INTERACTION AS EFFECTOR TRIGGERED IMMUNITY (ETI)
8Jones & Dangl (2006)
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OUTCOME OF R- AVR INTERACTION
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FUNCTIONS AND FEATURES OF AVR GENE CODED PROTEINS
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)
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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 .
RESISTANCE GENES
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
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MAJOR CLASSES OF R PROTEINSS. NO MAJOR R-GENE
CLASSESEXAMPLE
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
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13Agrios (2005)
TYPES OF R-CODED RECEPTOR PROTEINS
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GENE PLANT PATHOGEN YEAR ISOLATED
Pto Tomato Pseudomonas syringae pv. tomato (avrPto)
1993
PBS1 Arabidopsis Pseudomonas syringae pv. phaseolicola(avrPphB)
2001
RPS2 Arabidopsis Pseudomonas syringae pv. maculicola (avrRpt2)
1994
N Tobacco Tobacco Mosaic virus 1994
Bs2 Pepper Xanthomonas campestris pv. vesicatoria (avrBs2)
1999
RRS-1 Arabidopsis Ralstonia solanacearum 2002Pi-ta Rice Magnaporthe grisea(avrPita) 2000Cf-9 Tomato Cladosporium fulvum(Avr9) 1994Ve1Ve2
Tomato Verticillium albo-atrum 2001
Xa-21 Rice Xanthomonas oryzae pv.oryzae (all races)
1995
Pi-d2 Rice Magnaporthe grisea 2006
14 Gururani et.al.,2012
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Plant proteins belonging to the nucleotide-binding site–leucine-rich repeat (NBS-LRR) family are used for pathogen detection.
(R-PROTEIN)
Harmful organismRecognition by resistance protein
Signal to cell nucleus
Genetic material Defense
Response Defense protein (R-PROTEIN)
Out
side
pla
nt
cell
Insi
de p
lant
cel
l
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 IN ACTION
NBS-LRRPROTEIN
(R-GENE)
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MODELS FOR R- AVR GENE INTERCTION
• 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
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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
17Staskawicz et.al.,1995
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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
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19Jones & Dangl (2006)
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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.
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Jones & Dangl (2006)
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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 binding22
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23Zhang et.al., 2013
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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 mimicsthe 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
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25Zhang et.al., 2013
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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
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27Collier and Moffett (2009)
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MOLECULAR BASIS FOR PLANT- FUNGUS INTERACTIONS
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UTILIZATION OF AVIRULENCE GENE FOR CONTROL OF PLANT PATHOGENS
DIRECT UTILIZATION THROUGH TWO COMPONENT SENSOR SYSTEM (De Witt , 1992)
40Lauge and De Wit (1998)
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INDIRECT UTILIZATION OF AVIRULENCE GENES
GENE DEPLOYMENT
GENE PYRAMIDING
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Virulence/ avirulence pattern
Gene Deployment
V1 / avr2, avr3 R2, R3, not R1V2 , V3 / avr1 Only R1
V1, V2, V3/ avr4, avr5 R4, R5
R1
R1 + R2
R1 + R2+ R3
eg. Oat against crown rust
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MULTILINES
R1
V1
R2
V2
R3
V3
R4
V4
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CO-EVOLUTION OF RUST AVR AND HOST R GENEFLAX 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.
44Jones & Dangl (2006)
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CONCLUSION
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FUTURE PROSPECTS
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.
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