Transcript TAL effectors

Stratégies parasitaires chez Xanthomonas
Boris SZUREK
Montpellier
France
[email protected]
Plant – Bacteria co-evolution Zig-Zag model
Plant defense level
Jones et Dangl, 2006. The plant immune system. 444:323-329. Nature.
HR
Specific resistance
Basal resistance
effectors
effectors
Avr
receptor
R
Avr
R
PAMP
PAMPS
Loss of
or modification of
or acquisition of
Evolution
Time
Plant – Bacteria co-evolution Zig-Zag model
Plant defense level
Jones et Dangl, 2006. The plant immune system. 444:323-329. Nature.
HR
Specific resistance
Effector-Triggered Susceptibility (ETS)
Basal resistance
effectors
effectors
Avr
receptor
R
Avr
R
PAMP
PAMPS
Loss of
or modification of
or acquisition of
Evolution
Time
Plant – Bacteria co-evolution Zig-Zag model
Plant defense level
Jones et Dangl, 2006. The plant immune system. 444:323-329. Nature.
HR
Specific resistance
Effector-Triggered Susceptibility (ETS)
Effector-Triggered Immunity (ETI)
Basal resistance
effectors
effectors
Avr
receptor
R
Avr
R
PAMP
PAMPS
Loss of
or modification of
or acquisition of
Evolution
Time
TAL (Transcription Activator-Like) Type III effectors
Repeats
NLS AD
N
C
DNA binding, specificity
translocation
nuclear
localization
transcriptional
activation
Plant cell
Transcripts
Bacteria
TAL
effector
TAL effectors
• localize to host nucleus
• induce expression of host genes
• some are essential virulence factors
Nucleus
TAL (Transcription Activator-Like) Type III effectors
Repeats
NLS AD
N
C
DNA binding, specificity
translocation
nuclear
localization
transcriptional
activation
Plant cell
Transcripts
Bacteria
TAL
effector
Xanthomonas spp.
X. campestris pv. campestris
TALs per
strain
0-4
X. campestris pv. vesicatoria
0-1
X. campestris pv. armoraciae
0-3
X. citri
1-4
X. campestris pv. malvacearum
6-10
X. oryzae pv. oryzae
7-16
X. oryzae pv. oryzicola
12-26
Ralstonia solanacearum
Nucleus
Ralstonia solanacearum
1
The TAL effector AvrBs3 (U. Bonas lab)
Xanthomonas campestris pv. vesicatoria
• pathogen of pepper and tomato
17.5 repeats
AvrBs3
Hypertrophy
HR
pictures: S. Kay
susceptible pepper (bs3)
resistant pepper (Bs3)
Model of AvrBs3 function
U. Bonas-lab: Kay et al. 2007 Science 318:648
T. Lahaye/U.Bonas-lab: Römer et al. 2007 Science 318:645
upa-Gen
DNA-binding:
Simone Hahn
UPA-Box
UPA20
Bs3
other
UPA genes
bHLHtranscription factor
UPA7
a-expansin
UPA13
transcription
factor
slide: modified from S. Kay
TAL effectors roles in plant disease and resistance
Susceptibility
TAL- ETS
SWEET/nodulin-3 proteins
. > 20 members in rice
. Transporters
. Glucose & sucrose export / copper uptake
Talbot., 2010, Nature
TAL effectors roles in plant disease and resistance
Susceptibility
Resistance
?
TAL effectors roles in plant disease and resistance
Susceptibility
Resistance
TAL- ETI
TAL effectors roles in plant disease and resistance
Susceptibility
Resistance
TAL effectors roles in plant disease and resistance
Susceptibility
Resistance
}
Ineffective
TAL- ETS
How is the specificity of TAL effectors encoded ?
upa
UPA-Box
How is the specificity of TAL effectors encoded ?
upa
UPA-Box
AvrBs3 induces expression of upa genes
• AvrBs3 binds to DNA
• AvrBs3 repeat region alone binds UPA-box in vitro
• Repeats determine specificity
The TAL code revealed
Boch et al. (2009) Breaking the code of DNA binding
specificity of TAL-type III effectors. Science 326:1509-1512;
published online 29 October 2009 (10.1126/science.1178811).
Moscou and Bogdanove (2009) A simple cipher governs
DNA recognition by TAL effectors. Science 326:1501;
published online 29 October 2009 (10.1126/science.1178817).
picture: Adam Bogdanove
AvrBs3 repeat types
• 12 + 13: “hypervariable”
• 4 repeat types in AvrBs3
HD, NI, NG, NS
modified from:
Schornack et al. (2006) J. Plant Physiol. 163:256.
Correlation between repeat types and UPA box
UPA box consensus
DNA
Repeats
T
A
T
A
T
A
A
A
C
C
T
N
N
C
C
C
T
C
T
HD NG NS NG NI NI NI HD HD NG NS NS HD HD HD NG HD NG
AvrBs3
17.5 x 34 aa
NH2
COOH
1
12/13
3
4
LTPEQVVAIASHDGGKQALETVQRLLPVLCQAHG
NI
NG
NS
1.) 1 AvrBs3-repeat corresponds to 1 bp
2.) Most repeat types favor a specific bp
"Breaking the code"
Effector – target sites
AvrBs3 – Bs3, UPAs
AvrBs3Drep109 – Bs3
AvrHah1 – Bs3
AvrBs3Drep16 – Bs3E
AvrXa27 – Xa27
PthXo1 – Os8N3/Xa13
PthXo6 – OsTFX1
PthXo7 – OsTFIIAg1
test the model!
Hax2, Hax3, and Hax4 from X. campestris
• 3 TAL effectors from Arabidopsis-pathogenic Xc, unknown specificity
• Hax3 and Hax4: 34-aa repeats
• Hax2: 35-aa repeats
Kay et al. (2005) MPMI 18:838-848.
Target specificity of Hax2, Hax3, and Hax4
Target specificity of repeat types
Target specificity of repeat types
Artifical TAL effectors with novel specificities
Summary
• TAL effectors recognize target DNA with novel DNA-binding domain
• 1 repeat corresponds to 1 bp
• 2 hypervariable amino acids / repeat determine specificity
• Rearranging repeats yield new DNA-binding specificities (biotech)
The Crystal Structure of TAL Effector PthXo1 Bound to Its DNA
Target
Mak et al., Science, 2012
Summary
. TAL effectors are highly customizable DNA binding proteins
. They can be fused to a nuclease and used for genome engineering (TALEN)
. They can be used as custom transcriptional activators
. Other uses, including gene repression, point mutagenesis,
and modification of epigenetic marks, can be envisioned
. Tools exist for quick, cheap, and easy synthesis of TAL effector constructs
. Many questions remain:
- contribution of individual RVD-nucleotide associations to affinity
- relation of length to specificity
- biophysical nature of interactions (minimal DNA binding domain)