FROM SEED-GERMINATION TO FLOWERING, LIGHT CONTROLS PLANT DEVELOPMENT VIA THE PIGMENT PHYTOCHROME

Plant growth and development are regulated by interactions between the environment and endogenous developmental programs. Of the various env ironmental factors controlling plant development, light plays an espec ially important role, in photosynthesis, in seasonal and diurnal time sensing, and as a cue for altering developmental pattern. Recently, se veral laboratories have devised a variety of genetic screens using Ara bidopsis thaliana to dissect the signal transduction pathways of the v arious photoreceptor systems. Genetic analysis demonstrates that light responses are not simply endpoints of linear signal transduction path ways but are the result of the integration of information from a varie ty of photoreceptors through a complex network of interacting signalin g components. These signaling components include the red/far-red light receptors, phytochromes, at least one blue fight receptor, and negati ve regulatory genes (DET, COP, and FUS) that act downstream from the p hotoreceptors in the nucleus. In addition, a steroid hormone, brassino lide, also plays a role in light-regulated development and gene expres sion in Arabidopsis. These molecular and genetic data are allowing us to construct models of the mechanisms by which light controls developm ent and gene expression in Arabidopsis. In the future, this knowledge can be used as a framework for understanding how all land plants respo nd to changes in their environment.