Poster: Photomorphogenesis

Abs # 514: Regulation of phyB localization in Arabidopsis

Presenter:	Chen, Meng , mchen@salk.edu
Authors	Chen, Meng  (A)   Schwab, Rebecca  (A)   Fankhauser, Christian  (B)   Chory, Joanne  (A)
Affiliations:	(A): Howard Hughes Medical Institute, The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA. (B): Institute for Plant Sciences, Swiss Federal Institute of Technology, ETH Center, Zurich, Switzerland

Phytochrome, the red and far-red photoreceptor, is essential for plants to monitor light quantity, quality, and periodity to optimize their development and growth. The bilin containing photoreceptor has two forms, a red light absorbing Pr form and a far-red light absorbing Pfr form. Pr and Pfr forms are inter-convertible upon absorption of corresponding light. Traditionally the Pfr form has been considered as the active form. Phytochrome is synthesized in the cytoplasm in the Pr form in the dark. Nuclear import and nuclear body formation are the earliest responses of phytochrome upon light illumination. However, the function of phytochrome nuclear bodies and the regulation of both phyB nuclear import and nuclear body formation are still largely unknown. In this presentation, first, we are going to demonstrate evidences supporting PKS1 (a phytochrome interacting protein and a negative regulator of the phyB pathway) as a cytoplasmic retention factor to attanuate phyB nuclear import. Secondly, we characterized the steady-state phyB localization patterns under different light conditions and developmental stages using a phyB::GFP line. We found that PhyB localization pattern was dependent on the percentage of the Pfr form. Besides light, internal developmental signals could also affect phyB localization patterns. Based on the understanding of the dynamic of phyB nuclear body formation, a genetic screen was performed on the phyB::GFP line looking for red light hyposensitive mutants with mislocalization phyB::GFP. Both intrinsic and extrinsic mutants were isolated in this screen. The second site mutations defined loci in the genome involved in the phyB nuclear body formation and signaling.