Structure-Function Studies on Phytochrome: Light perception by phytochrome initiates many developmental and physiological responses in green plants. Research outlined in this proposal will provide new information regarding both phytochrome structure and the primary signal transduction process(es) initiated by phytochrome photoactivation in both a higher plant and a green alga. Studies on both phytochromes will include a) delineation of regions of light-induced conformational changes in the protein moiety, b) characterization of conserved regions of primary structure between the higher plant and algal phytochromes and c) elucidation of structural features which confer heterogeneity to the purified photoreceptor. With regard to the primary function of phytochrome in plant cells, the hypothesis that phytochrome is a protein kinase or is functionally associated with a protein kinase, will be tested. These studies will include a) delineation of the sites and stoichiometry of ATP (or other nucleotide) binding on phytochrome, b) demonstration whether the kinase co-purifies with phytochrome and c) determination whether phytochrome photoactivation alters protein phosphorylation of endogenous or exogenous substrates both in vivo and in vitro. In vivo and in vitro substrates for the "phytochrome-associated" protein kinase will be compared. Environmental photoperception by phytochrome is essential to optimal growth and development of plants. In the natural environment, plants are exposed to extremes in light intensity and spectral quality. Phytochrome serves as a molecular sensor of such changes by modulating the state of development of the plant via changes in gene expression (cf. induction of seed germination or flowering) as well as influencing growth rate or chloroplast orientation to optimize light capture for photosynthesis. The experiments outlined in this proposal will provide new information regarding both phytochrome structure and the components of the signal transduction initiated by phytochrome photoactivation. It is anticipated that an understanding of the phytochrome-mediated signal transduction process at a molecular level will foster new approaches to improve plant productivity using molecular genetic and biochemical tools.
