Julia Rausenberger Zentrum für Biosystemanalyse Universität Freiburg An integrative and quantitative model for phyB mediated photomorphogenesis: From protein dynamics to physiology Julia Rausenberger Zentrum für Biosystemanalyse Universität Freiburg GRK Begutachtung 18. Februar 2010

Aspects of photomorphogenesis Adapted from Quail (2002) red light Skotomorphogenesis vs. Photomorphogenesis Alternative developmental programs during early plant growth: light-dependent de-etiolation Phytochrome B: Dimeric protein about 125kDa Abundant in red light (660nm) Two reversibly photointerconverting forms Nuclear complexes early, transient late, stable Mediated reactions: Growth of hypocotyl length Magnitude of cotyledon areas Taken from Bae & Choi (2008)

What makes the phytochrome system interesting for theoreticians? Pr  = 0.85 k1, 660 nm k2, 660 nm Pfr R Pr Pfr  = 0.03 k1, 730 nm k2, 730 nm FR at equilibrium: d[Pfr]/dt = 0 = k1[Pr] - k2[Pfr] [Pfr]/[Ptot] =  = k1 / (k1 + k2) Pr Pfr k1 k2 Adjustable parameters: spectral composition of incident light light intensity (photon flux) duration of irradiation protein dynamics can be changed by switching on/off the light

Time resolved hypocotyl growth Darkness Continuous red light phyB-9 Col WT phyB-OX Hypocotyl growth is a standard read-out for phytochrome signaling. When grown in darkness, the three phenotypes show the same S-shaped growth profile. Light-grown seedlings also exhibit an S-shaped growth curve, but the final hypocotyl length vary due to the presence of active phytochrome. No active phytochrome present How does active phytochrome influence hypocotyl growth?

Investigations of growth patterns Hypocotyl dark growth is characterized by: Asymmetric S-shaped growth curve L Asymmetric bell-shape of velocity function dL/dt -> growth rate is not constant over time J. Sachs (1874): ”large period of growth”: growth velocity increase -> maximum -> growth velocity decrease G. Backman (1931): Integration of the growth velocity yields S- shaped growth curve: “growth cycle”  γ determines the asymmetry of L and dL/dt Biological time Growth rate Environmental limitation

How does active phytochrome come into play? End-point-analysis (after 4 days) darkness continuous red light Biological time Modified growth rate Environmental limitation Scale bar = 10μm