Skotomorphogenesis

Seed germination

Genes and enzymesEmbryo and

Seed development

Plant life cycle

Photomorphogenesis

Photoreceptors

Phytochrome

Cells and cell growth

Phytochrome: regulation oflight responses

SKOTOMORPHOGENESIS

Photomorphogenesis Skotomorphogenesis

What is not regulated by light ???

Cotyledon expansion

Reduced hypocotylelongation

Open apical hook

closed apical hook Non-expanded

cotyledons

Etiolated hypocotyl

Is skotomorphogenesis achived via active repression of photomorphogenesis

Light regulation mutants

Shorthypocotyl

Expanded cotyledons

Open apical hook

Skotomorphogenesis in the light

Germination of lettuce seeds (photoreversibility)

Red light

Far-red light

inactive active

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

Strasburger, 2002

Shade avoidance reaction

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

GA signaling

Nuclear import

DNA binding

Gene activation

phytochrome signaling

Nuclear import

DNA binding

Gene activation

Light regulation mutants

Shorthypocotyl

Expanded cotyledons

Open apical hook

Light regulation through COP1

Photoreceptors for different light qualities

Downstream transcription factors

CRY1 and CRY2 are negativeregulators of COP1

COP1 marks transcription factors for degradation (E3 ubiquitin ligase)

Cop1 interaction with cryptochrome

CRY1 is inactive in the dark CRY1 inhibits COP1 under blue light

Electron transfer reaction

Cop1 complexes in plants and animals

Plants: light regulated degradation of photoreceptor elements

Animals: degradation of protooncogene transcription factors

Negative regulation of light signaling (HY5, LAF1) Induction of tumorigenesis (p53, cJUN)

Light regulation through COP1

COP1 CRY1

COP1 CRY1

Hy5UbUbUbUbHy5

nucleus

light dark