9407864 Sharrock This award addresses the general question of how plants sense the environmental light cues that control their physiological and developmental processes. More specifically, the proposal tests a model for the organization and function of a plant regulatory photoreceptor system, the red/far red light-sensing phytochrome family. In this model, covalent linkage of a light-absorbing chromophore to the diverse family of phytochrome (PHY) apoproteins gives rise to a heterogeneous population of photoreceptors which have differential roles in control of photomorphogenesis and may be differentially expressed in various plant cell types. Work from the preceding grant has shown that five phytochrome apoproteins are encoded by a PHY gene family in Arabidopsis thaliana and that similar though not identical PHY gene families are present in all flowering plants. An understanding of the individual roles of the phytochromes in light control of plant physiology and development is clearly an important goal. In the current funding period, major emphasis is placed on analysis of the functions and the regulation of the recently identified fourth and fifth Arabidopsis phytochromes, PHYD and PHYE, and on the structural determinants of phytochrome functional specificity. The research directly addresses basic questions concerning the organization of a plant photoreceptor family and the mechanisms of light-activated plant developmental responses. Moreover, many phytochrome-controlled responses are components of important agronomic traits such as seed germinatiion, yield, and flowering time. Hence, the phytochrome receptors are likely targets for future modification in crop plants via plant biotechnology. ***
