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Phytochrome signalling modulates the SA-perceptive pathway in Arabidopsis

This study investigates the interaction between phytochrome signalling and the salicylic acid (SA) pathway in Arabidopsis. It examines how phytochrome affects the synthesis of PR proteins and defense against pathogens. The role of SA-hydroxylase gene in SA degradation is also analyzed. The results show that light and phytochrome-dependent mechanisms modulate defense responses through the SA pathway.

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Phytochrome signalling modulates the SA-perceptive pathway in Arabidopsis

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

  2. 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 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

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

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

  5. 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.

  6. 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

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

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

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

  10. 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 TableS1Effect 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

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

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