Chromophore-protein interactions in phytochromes in connection with the control of the High Irradiance Response (HIR)

• Applicant: Professorin Dr. Silvia E. Braslavsky
• Subject Area: Biophysics
• Term: from 2001 to 2004
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5301346

In the model species Arabidopsis thaliana five genes encode dirvergent phytochrome apoproteins. Of particular interest is the versatile behaviour of phytochrome A (phyA), the most abundant phytochrome in dark-grown plants. Surprisingly, phyA mediates not only the response to very low fluences of light (very low fluence response, VLFR), such as germination induction of buried seeds, but also the response to prolonged far-red light exposure (high irradiance response, HIR), such as seedlings growth beneath foliage. The possible relationship between the photochemical behaviour of phyA and the HIR will be investigated using two approaches: study of (1) photochemical properties of recombinant mutated phyA biologically characterised as deficient in its ability to mediate HIR while retaining the VLFR, and of (2) the biological activity of phyA apoprotein assembled with synthetic chromophores unable to produce the kinetics observed with phytochromobilin. For (1), the clones of mutated phyA will be obtained in Casal's group, their use for apoprotein expression as well as the apoprotein assembly with phytochromobilin and phycocyanobilin will be carried out in Gärtner's group (Mülheim). Time-resolved photochemical studies will be performed in Braslavsky's group. For (2), chromophores isolated and/or synthesysed in Gärtner's group will be used. The biological activity of the assembled phyA will be studied in Casal's group.

• DFG Programme: Research Grants