phytochrome signalling modulates the sa- perceptive pathway in arabidopsis
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Phytochrome signalling modulates the SA-perceptive pathway in Arabidopsis
ChloroplastPhotosynthetic light reaction
Calvin cycleStarch synthesisProtein synthesisPhotorespiration
Amino acid biosynthesisChlorophyll and/or heme biosynthesis
Nitrogen assimilationSulfur assimilation
Peroxisomephotorespiration
MitochondrionTCA cycle
PhotorespirationBrassinosteroid biosynthesis
MicrosomePhenylpropanoid pathways
CytosolProtein synthesisSucrose synthesis
GlycolysisUbiquitin-proteasome pathwayBrassinosteroid biosynthesis Golgi appatatus
Plasma membraneCell wall synthesis
NucleusTranscription factorsTranscription factors
GlyoxysomeGlyoxidate cycle
Fatty acid oxidation
Endoplasmic reticulumCell wall synthesis
VacuoleWater transport
Ethylene synthesis
Blue light
Far-red light
Red light
CRY1
phyA
phyB COP1
COP1
Hypocotylelongation
Hypersensitive response
Infection
SA -glucoside
SA Methylsalicylate
Methylsalicylate
SystemicAcquiredresistance
SA
SA -glucoside
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)thiadiazole-7-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.
The salicylic acid (SA) pathway
SA
Phytochrome A
Phytochrome B
LTD(light to defense)
Chloroplast
PSI2
Unknown signal
PR1PR5
HR
Interaction of Phytochrome Signalling with The SA Signal Transduction Pathway
Structures of SAR-inducing compounds
2,6-dichloroisonicotinic acid Benzo(1,2,3)thiadiazole-7-carbothioic 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.
Cab2--luc expression(counts per seedling/15min)
ChS--luc expression (counts per seedling/15min)
No treatment 6.2 2.8
5' red light 122.0 72.3
SA (250 M) 6.7 3.0
BTH (1 mM) 7.2 3.7
SA (250 M) + 5' red light 119.7 68.0
BTH (1 mM) + 5' red light 103.6 61.1
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 mol m-2 s-1). Each value represents the average response of two sets of 150 seedlings
Ferric enzyme Compound I
H2O+O2 H2O2
H2O2 H2O
Ferric enzyme Compound I
Compound II
H2O2 H2OSA•(+H2O)
SA
SA
SA•
(A)
(B)
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 M 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)
Wt 7.4 (0.5) 2.1 (0.8) 5.3 (0.8) 16.3 (2.1)phyA-phyB 7.7 (0.4) 0.8 (0.7) 7.8 (0.6) 3.2 (0.6)psi2 7.3 (0.7) 2.3 (0.9) 4.1 (0.4) 35.8 (4.2)phyA-phyB-psi2 7.7 (0.6) 1.3 (0.7) 7.7 (0.4) 3.6 (0.5)NahG 7.5 (0.5) 0.5 (0.3) 7.9 (0.5) 2.8 (0.4)NahG-psi2 7.6 (0.8) 0.4 (0.2) 7.8 (0.5) 4.0 (0.5)
aPlants 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.
Plants:
Dark (0.1 µmol m-2 sec-1) Light (25 µmol m-2 sec-1)
Bacterial titrea (± SD)
PR1 expressionb (± SD)
Bacterial titrea (± SD)
PR1 expressionb (± SD)
3681 mutant containing green and white areas
Single mutant 3681-variegated Triple mutant 3681-variegated phyA-phyB
Double mutant 3681-variegated psi2 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.
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