This proposal addresses the question of how the light cues that control plant physiological and developmental processes are perceived. Currently, the only plant regulatory photoreceptor that has been isolated is the red/far red light-responsive chromoprotein phytochrome. Preliminary studies show that three to five divergent phytochrome apoproteins are encoded by a phy gene family in Arabidopsis thaliana and that similar phy gene families are present in many, perhaps all, flowering plants. It is proposed that in vivo attachment of a light-absorbing chromophore to the phy polypeptides generates a multi-component red/far red-sensing photoreceptor system. The goals of this project are to: 1) determine the sequences of all of the A. thaliana phytochromes from phy gene and cDNA clones, 2) analyze the regulation and localization of the phy mRNAs, and 3) assign functions in photoregulation of plant growth and reproduction to specific phytochromes by analyzing A. thaliana photomorphogenic mutants. This investigation addresses fundamental questions concerning the complexity of plant photoreceptor systems and the mechanism of the initial steps of plant light perception. A large number of plant cellular and developmental processes including gene expression, growth rate, cellular differentation, and timing of reproduction are responsive to the light environment. Physiological experiments indicate that there are at least three major pigment systems active in perception of light cues, one of which is the red/far red light-responsive pigment known as photoreceptor phytochrome. Biochemical and immunological studies suggest that there is more than one form of phytochrome. Since no specific physiological function has been assigned to any of the phytochromes, it is clearly possible that each carries out a specific role in light perception. Up to this time, however, it has been very difficult to identify unambigously these individual pigment proteins and determine their functions. The isolation of DNA clones corresponding to these proteins and the development of specific molecular probes to distinguish among them will lead to rapid advances in this field and a better understanding of their role in plant growth and development.*** //
