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Phytochrome signalling modulates the SAperceptive pathway in Arabidopsis
Cytosol
Chloroplast
Photosynthetic light reaction
Calvin cycle
Starch synthesis
Protein synthesis
Photorespiration
Amino acid biosynthesis
Chlorophyll and/or heme biosynthesis
Nitrogen assimilation
Sulfur assimilation
Protein synthesis
Sucrose synthesis
Glycolysis
Ubiquitin-proteasome pathway
Brassinosteroid biosynthesis
Golgi appatatus
Plasma membrane
Cell wall synthesis
Nucleus
Transcription factors
Transcription factors
Peroxisome
photorespiration
Endoplasmic reticulum
Cell wall synthesis
Microsome
Phenylpropanoid pathways
Mitochondrion
Glyoxysome
TCA cycle
Photorespiration
Brassinosteroid biosynthesis
Glyoxidate cycle
Fatty acid oxidation
Vacuole
Water transport
Ethylene synthesis
Hypocotyl
elongation
Blue light
CRY1
Far-red light
phyA
Red light
phyB
COP1
COP1
Systemic
Acquired
resistance
Hypersensitive
response
Methyl
salicylate
SA
Infection
SA
SA b-glucoside
SA b-glucoside
Methyl
salicylate
The salicylic acid (SA) pathway
The salicylic acid (SA) pathway is an important route inserted in the
network of defense signalling.
The synthesis of PR proteins can be activated by an ectopic treatment
with SA or functional analogues such as BTH (benzo(1,2,3)thiadiazole7-carbothioic acid S-methyl ester).
In transgenic Arabidopsis plants expressing a SA-hydroxylase gene of
Pseudomonas putida (NahG gene), SA is degraded to catechol leading to
a loss of PR1 gene expression, and a higher susceptibility to virulent
pathogens.
Interaction of Phytochrome Signalling with
The SA Signal Transduction Pathway
SA
LTD
(light to defense)
PR1
PR5
Phytochrome A
Chloroplast
Phytochrome B
PSI2
Unknown signal
HR
Structures of SAR-inducing compounds
2,6-dichloroisonicotinic acid
Benzo(1,2,3)thiadiazole-7carbothioic acid S-methy ester
Figure 1. The SA and BTH induction of PR1 and chlorophyll is
light dependent
Figure 2. The modulation of defense by light is phytochrome-dependent.
Table S1 Effect of red light on the induction of CAB and ChS
expression. Five-day-old seedlings grown in darkness were treated
with SA or BTH alone, or in conjunction with a pulse of 5 min red light
(25 mmol m-2 s-1). Each value represents the average response of two
sets of 150 seedlings
Cab2-W-luc expression
ChS-W-luc expression
(counts per seedling/15min)
(counts per seedling/15min)
No treatment
6.2
2.8
5' red light
122.0
72.3
SA (250 mM)
6.7
3.0
BTH (1 mM)
7.2
3.7
SA (250 mM) + 5' red light
119.7
68.0
BTH (1 mM) + 5' red light
103.6
61.1
(A)
H2O+O2
H2 O2
Ferric enzyme
Compound I
H2 O2
H2 O
(B)
Ferric enzyme
SA•
(+H2O)
Compound I
H2 O2
SA
Compound II
H2 O
SA•
SA
Potential targets in mammalian cells include:
• Postaglandin H synthetase
• Lactoperoxidase
• Myeloperoxidase
• Catalase
• Aconitase
• Methemoglobin
• Metmyoglobin
Potential targets in plants include:
• Hydroperoxide dehydrase
• Ascorbate peroxidase
• Horseradish peroxidase
• Catalase
• Aconitase
• Leghemoglobin
• Aminocyclopropane carboxylic acid(ACC) oxidase
Figure 3. SA content is not correlated to phytochrome activity.
Figure S1 The light modulated expression of PR1 in SA-treated
plants is independent of protein synthesis. Three-week-old WT plants
were pretreated with cycloheximide, injected with 250 mM SA, and
exposed to high light fluences for 30 min.
Table 1. Effect of light perception on the expression of PR genes and the
growth of an avirulent pathogen (Pseudomonas syringae pv. tomato
DC3000 carrying avrRpt2)
Dark (0.1 µmol m-2 sec-1)
Plants:
Wt
phyA-phyB
psi2
phyA-phyB-psi2
NahG
NahG-psi2
aPlants
Light (25 µmol m-2 sec-1)
Bacterial titrea
(± SD)
PR1 expressionb
(± SD)
Bacterial titrea
(± SD)
7.4 (0.5)
7.7 (0.4)
7.3 (0.7)
7.7 (0.6)
7.5 (0.5)
7.6 (0.8)
2.1 (0.8)
0.8 (0.7)
2.3 (0.9)
1.3 (0.7)
0.5 (0.3)
0.4 (0.2)
5.3 (0.8)
7.8 (0.6)
4.1 (0.4)
7.7 (0.4)
7.9 (0.5)
7.8 (0.5)
PR1 expressionb
(± SD)
16.3 (2.1)
3.2 (0.6)
35.8 (4.2)
3.6 (0.5)
2.8 (0.4)
4.0 (0.5)
were injected with a solution of 0.5 X10 3 bacteria cm 2 and the number of
colony forming units were measured 3 days after injection; data are expressed in Log
cfu cm 2.
bRelative abundance.
3681 mutant containing green and white areas
Single mutant 3681-variegated
Double mutant 3681-variegated psi2
Triple mutant 3681-variegated phyA-phyB
Double mutant 3681-variegated psi2
containing the NahG transgene
Figure 4. Influence of
chloroplasts on the
phytochrome-modulated
defense responses.
Figure 5. Schematic
representation of the
modulation of defense
by phytochrome using
intuitive (a) and Boolean
formalism (b).
Figure S2 The expression of a defensin gene is not upregulated by light:
Expression of PDF1.2 under increasing light intensity.