1. Phytochrome signalling modulates the SA-perceptive pathway in Arabidopsis

4. Endoplasmic reticulum
Cytosol
Protein synthesis
Sucrose synthesis
Glycolysis
Ubiquitin-proteasome pathway
Brassinosteroid biosynthesis
Chloroplast
Photosynthetic light reaction
Calvin cycle
Starch synthesis
Protein synthesis
Photorespiration
Amino acid biosynthesis
Chlorophyll and/or heme biosynthesis
Nitrogen assimilation
Sulfur assimilation
Golgi appatatus
Plasma membrane
Cell wall synthesis
Nucleus
Transcription factors
Peroxisome
photorespiration
Endoplasmic reticulum
Cell wall synthesis
Microsome
Phenylpropanoid pathways
Mitochondrion
TCA cycle
Photorespiration
Brassinosteroid biosynthesis
Vacuole
Water transport
Ethylene synthesis
Glyoxysome
Glyoxidate cycle
Fatty acid oxidation

6. COP1 COP1 Blue light CRY1 Far-red light phyA Red light phyB Hypocotyl
elongation
COP1
COP1
Blue light
CRY1
Far-red light
phyA
Red light
phyB

7. Systemic
Acquired
resistance
Methyl
salicylate
Hypersensitive
response SA
Infection
SA b-glucoside SA
Methyl
salicylate
SA b-glucoside

8. 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)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.

9. Interaction of Phytochrome Signalling with The SA Signal Transduction Pathway
PR1
PR5 SA
LTD
(light to defense)
Phytochrome A
Chloroplast HR
Phytochrome B
PSI2
Unknown signal

10. Structures of SAR-inducing compounds
Benzo(1,2,3)thiadiazole-7-
carbothioic acid S-methy ester
2,6-dichloroisonicotinic acid

11. Figure 1. The SA and BTH induction of PR1 and chlorophyll is light dependent

12. Figure 2. The modulation of defense by light is phytochrome-dependent.

13. 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 (counts per seedling/15min)
ChS-W-luc expression (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

14. (A) (B) H2O+O2 H2O2 Ferric enzyme Compound I H2O2 H2O Ferric enzyme
SA•
(+H2O) SA SA
SA•
Compound II

15. 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
• Leghemoglobin
• Aminocyclopropane carboxylic acid(ACC) oxidase

16. Figure 3. SA content is not correlated to phytochrome activity.

17. 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.

18. 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)
Light (25 µmol m-2 sec-1)
Plants:
Bacterial titrea (± SD)
PR1 expressionb (± SD)
Bacterial titrea (± SD)
PR1 expressionb (± SD)
Wt (0.5) (0.8) (0.8) (2.1)
phyA-phyB (0.4) (0.7) (0.6) (0.6)
psi (0.7) (0.9) (0.4) (4.2)
phyA-phyB-psi (0.6) (0.7) (0.4) (0.5)
NahG (0.5) (0.3) (0.5) (0.4)
NahG-psi (0.8) (0.2) (0.5) (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.

19. 3681 mutant containing green and white areas

20. Single mutant 3681-variegated
Triple mutant 3681-variegated phyA-phyB
Double mutant 3681-variegated psi2
Double mutant 3681-variegated psi2 containing the NahG transgene

21. Figure 4. Influence of chloroplasts on the phytochrome-modulated defense responses.

22. Figure 5. Schematic representation of the modulation of defense by phytochrome using intuitive (a) and Boolean formalism (b).

23.                                                                                                                                            
Figure S2  The expression of a defensin gene is not upregulated by light: Expression of PDF1.2 under increasing light intensity.