9723124 Liscum Higher plant are dependent upon light not only as an energy source to drive carbon fixation, but also as a modulator of growth and development throughout their life cycle. Multiple wavelength regions of the electromagnetic spectrum can be utilized as regulatory cues of various developmental and morphological (photomorphogenic) responses through the action of several photoreceptor systems and associated signal transduction cascades. However, in most cases very little is known about the molecular basis for these response pathways. Our long-term objective is to elucidate the cellular and components of a plant light environment. Towards that end we have been using Arabidopsis thaliana (L.) Heynh, as a model system to investigate genetic and molecular basis of the phototropic response, or the differential growth response of various plant organs in response to directional light cues, and have identified mutants at several loci of that affect this response. Mutants in the nph4 (non-phototropic hypocotyl 4) allele series affect not only phototropism but also gravitropism and thigmotropism suggesting that NPH4 protein may be involved in the regulation og differential growth. We propose to: (a) Characterize a variety of physiological and developmental properties that require changes in growth for phenotypic expression (e.g., tropisms, light-dependent hypocotyl growth inhibition, inflorescence bolting) of the nph4 mutants in single mutant backgrounds, as well as in double and multiple mutant combinations with other phototropic and photomorphogenic mutants. (b) Clone and characterize the NPH4 gene. (c) Initiate studies to determine the biochemical function(s) of the NPH4 protein. (d) Use a variety of genetic screens (mutational, as well as biochemical) to identify additional components required for phototropism. (e) Use the photobiological characters elucidated from mutant analyses in our ongoing project to generate a genetic hierarchy for the regulation of phototropism. The rese arch proposed here should provide a wealth of information about a subset of the components of the phototropic signal-response system that are also necessary for additional tropic responses of higher plants. In addition, these studies may provide important insights into the mechanisms of how plant achieve and regulate differential growth.
