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.