Photomorphogenesis Skotomorphogenesis (etiolation)

Due to Pfr formation: Inhibition of hypocotyl elongation Inhibition of cotyledons translocation Increase of cotyledons surface area Unfolding of the cotyledon lamina Opening of hypocotyl hook Development of primary leaves Development of mature leaf primordia Increase of negative geotropism of the hypocotyl Development of xylem elements Differentiation of the stomata within the epidermis of the cotyledons Development of super-etioplasts in the cotyledons’ mesophyll Changes in the intensity of the cell respiration Synthesis of anthocyane in the cotyledons and the hypocotyl Increase of carotenoid biosynthesis Increase of chlorophyll biosynthesis Increase of RNA biosynthesis in cotyledons Increase of protein synthesis in cotyledons Increase of storage fat breakdown Increase of storage protein breakdown Increase of ethylene biosynthesis Acceleration of the Shibata-shift within the cotyledons Determination of the cotyledons’ capacity to photophosphorylate Modulation of the cotyledons’ enzyme synthesis

Phytochrome effects in monocots and dicots

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

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

Phytochrome regulation a) localization b) modification c) degradation

Shade avoidance reaction Strasburger, 2002

Shade avoidance reaction Strasburger, 2002

Shade avoidance reaction Strasburger, 2002

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

Gene activation through phytochrome Nuclear import DNA binding Gene activation

Phytochrome regulation

Pr Pfr biological activity Due to Pfr formation: Pr Pfr biological activity 660nm Pr Pfr 730nm fast slow degradation products

Photoreceptors make plants see the light

Photoreceptor mutants have an evolutionary disadvantage

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

Open apical hook Cotyledon expansion Reduced hypocotyl elongation

closed apical hook Non-expanded cotyledons Etiolated hypocotyl Is skotomorphogenesis achived via active repression of photomorphogenesis

How to perform genetic approaches to decifer light regulation in plants ???

Asking simple questions Photomorphogenesis in dark grown seedlings Skotomorphogenesis in light grown seedlings Asking simple questions How to perform genetic approaches to decifer light regulation in plants ???

Getting complicated answers !! Open apical hook Expanded cotyledons Short hypocotyl

Skotomorphogenesis in the light

Functions of HY gene products HY1, HY2, HY6 phytochrome chromophore biosynthesis HY3 phytochrome B HY8 phytochrome A HY4 chryptochrome1 (blue light receptor) HY5 bZIP transcription factor

Functions of cop/det gene products COP1 E3 ubiqutin ligase (phyA degradation) DET1 Interactor COP10, COP1 DDB1 (protein degradation) COP9 signalosome, proteasome complex DET2/DWF2 brassinosteroid biosynthesis

Measuring irradiation: chloroplast movements (Lemna) depending on light intensity Dark Low light High light

Measuring time Measuring time Measuring time Measuring time

Processes regulated by photoperiod flower induction begin and end of dormancy cambium activity growth rate formation of storage organs development of freezing resistance senescence

SD: 15 weeks 10hrs light SD: 14 weeks 10hrs light 1 week 24 hrs light SD: 12 weeks 10hrs light 3 weeks 24 hrs light

Short day plant Chrysanthemum Long day plant Spinach short day long day

R (660 nm) is effective; effect is eliminated by FR (730 nm) pulse Short day plant (long night) Long day plant (short night) R (660 nm) is effective; effect is eliminated by FR (730 nm) pulse

Flower induction depends on length of dark period per day Long day plants: days length longer than dark period Short day plants: day length shorter than dark period