Cells and cell growth Membranes and cell walls Fertilization and embryogenesis Seed development and dormancy Germination Water transport Water relations Plant nutrition Solute transport Gene function Skotomorphogenesis Photomorphogenesis Phytochrome

Three learning goals: - what is a phytochrome plant photoreceptor to govern light development requirements: light sensing ability signal transduction - phytochromes and their integration in development how phytochrome senses light and what happens then requirements: light sensitivity at particular wavelengths - phytochrome interactions with downstream proteins requirements: signal transduction apparatus that connects phytochrome activity with gene regulation

In a nutshell: phytochrome function

Phytochrome – plant signal transduction Environmental signal: light Receptor: phytochrome Signal transduction: PIF etc. Gene activation: PIGs Biological response: photomorphogenesis

Photomorphogenesis Skotomorphogenesis (etiolation)

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

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 Shade avoidance reaction

Sunlight and CO 2 have different effects on leaf morphology

What happens in the shade?

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 !!!

Strasburger, 2002 Shade avoidance reaction

Strasburger, 2002 Shade avoidance reaction

Strasburger, 2002 Shade avoidance reaction

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

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

Germination in dark and light

Gene activation through photoreceptors and PIF proteins Hemara