An integrative and quantitative model for phyB mediated photomorphogenesis:

From protein dynamics to physiology

Julia RausenbergerZentrum für Biosystemanalyse

Universität Freiburg

GRK Begutachtung18. Februar 2010

Adapted from Quail (2002)

red light

Aspects of photomorphogenesis

Skotomorphogenesis vs. PhotomorphogenesisAlternative developmental programs during early

plant growth: light-dependent de-etiolation

Taken from Bae & Choi (2008)

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

What makes the phytochrome system interesting for theoreticians?

• Adjustable parameters:– spectral composition of incident light– light intensity (photon flux)– duration of irradiation

Þ protein dynamics can be changed by switching on/off the light

PrPr

Pfr

= 0.03

k1, 730 nmk2, 730 nm

FR

Pr

= 0.85

k1, 660 nmk2, 660 nm

PfrPfr

R at equilibrium:

d[Pfr]/dt = 0 = k1[Pr] - k2[Pfr]

[Pfr]/[Ptot] = = k1 / (k1 + k2)

PrPr

PfrPfr

k1k2

Time resolved hypocotyl growth

No active phytochrome present

Darkness

phyB-9Col WTphyB-OX

Continuous red light

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

γ determines the asymmetry of L and dL/dt

Biological time

Growthrate

Environmentallimitation

• 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”

How does active phytochrome come into play?

darkness continuous red light

End-point-analysis (after 4 days)

Scale bar = 10μm

Biological time

Modifiedgrowth

rate

Environmentallimitation