Brassinosteroid mutants show dwarf phenotypes

Brassinosteroid signal transduction goes through kinases

Phytochrome – the classical photoreceptor

Development (realization of a phenotype from a genotype) is controlled by  endogenous factors intercellular regulation  phytohormones  exogenous factors biotic factors abiotic factors

Photomorphogenesis Skotomorphogenesis (etiolation)

Light has an influence on seedling development Photomorphogenesis  inhibition of hypocotyl elongation  opening of apical hook  cotyledon expansion  chloroplast development DarkLight

Dark Light wild-type cop/det mutants COP and DET proteins inhibit photomorphogenesis

Germination of lettuce seeds (photoreversibility) Reversible R/FR response system controlled by phytochrome germination

Pr Pfr Red light Far-red light inactive active Phytochrome dogma

synthesis germination, flower Induction…… red light far red light Phytochrome: from synthesis to action

blue lightred light

Arabidopsis: 5 phytochrome proteins (phyA - phy E), differ in their apoproteins Phytochrome : homodimeric chromoprotein: apoprotein and phytochromobilin (open chained tetrapyrrol) as chromophor form holoprotein

Strasburger, 2002 Structure of phytochrome proteins

Phytochrome responses vary with amount of light VLFR: µmol x m -2 LFR: µmol x m -2 Arabidopsis seed germination Lettuce seed germination Anthocyanin synthesis Inhibition of hypocotyl elong. Enlargement of cotyledons Apical hook opening HIR: >1000 µmol x m -2 x s -1

Phytochrome responses vary with amount of light Inhibition of hypocotyl elongation HIR: >1000 µmol x m -2 x s -1

Phytochrome responses vary with amount of light LFR: µmol x m -2 Lettuce seed germination

Strasburger, 2002 Phytochrome in seedlings

Strasburger, 2002 Shade avoidance reaction

Strasburger, 2002 Shade avoidance reaction

Strasburger, 2002 Shade avoidance reaction

Strasburger, 2002 Shade avoidance reaction

Strasburger, 2002 RFR PR inactive PFR active P FR active P R inactive sensor signal transduction Regulatory function

PHYA-GFP and PHYB-GFP fusion proteins migrate into the nucleus PHYA-GFP PHYB-GFP Dark Red

Gene activation through phytochrome Nuclear import DNA binding Gene activation

Pr Pfr Red light Far-red light Photoequilibrium: 660 nm 80% Pfr 730 nm 2-3% Pfr R/FR Sunlight:1.13 Dusk: 0.8/0.9 Shade of leaves:0.2 inactiveACTIVE !!!

Red light Far-red light Pr Pfr Two holoproteins (+chromophore) form a dimer Histidine kinase related Chromophore binding domain IIA IA IIB IB IA IIA IIBIB

N-terminal extension Hinge region PAS domain Histidine kinase related 1 Histidine kinase related 2 Chromophore binding domain The Phytochrome apoprotein (-chromophore) is a 125kD monomer Chromophore binding domains Two holoproteins (+chromophore) form a dimer IIA IA IIB IB