Cells and cell growthMembranes and cell walls Fertilization and

embryogenesis

Seed development and dormancy

Germination

Water transport

Water relations

Plant nutrition

Solute transport

Gene function

SkotomorphogenesisPhotomorphogenesis

Phytochrome

Three learning goals:

- what is a phytochrome

plant photoreceptor to govern light development

requirements:light sensing abilitysignal transduction

- phytochromes and their integration in developmenthow 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 germination

Pr PfrRed light

Far-red light

inactive active

Phytochrome dogma

synthesisgermination,flower Induction……

red light

far red light

Phytochrome: from synthesis to action

blue light red 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

R FR

PRinactive

PFRactive

PFR

active

PR

inactive

sensor signal transduction

Regulatory function

Strasburger, 2002

Structure of phytochrome proteins

Phytochrome responses vary with amount of light

VLFR: 0.00001 µmol x m-2

LFR: 1-1000 µmol x m-2

Arabidopsis seed germination

Lettuce seed germination

Anthocyanin synthesisInhibition of hypocotyl elong.Enlargement of cotyledonsApical 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: 1-1000 µmol x m-2

Lettuce seed germination

Strasburger, 2002

Shade avoidance reaction

Sunlight and CO2 have different effects on leaf morphology

What happens in the shade?

Pr PfrRed light

Far-red light

Photoequilibrium:

660 nm 80% Pfr730 nm 2-3% Pfr

R/FRSunlight: 1.13

Dusk: 0.8/0.9

Shade of leaves:0.2

inactive ACTIVE !!!

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

Dark Red

Gene activation through phytochrome

Nuclear import

DNA binding

Gene activation

Red light

Far-red light

PrPfr

Two holoproteins (+chromophore) form a dimer

Histidine kinase related

Chromophore binding domain

IIAIA

IIBIB

IA IIA

IIBIB

Germination in dark and light

Gene activation through photoreceptors and PIF proteins

Hemara