| Description: | Our long-term goal is to understand at the molecular levelhow plants perceive changes in their light environment, transduce those signals to their site(s) of action, and ultimately respond in the proper adaptive manner. One light- dependent response we are examining is the phototropic response, which represents an ideal physiological system for the study of not only light-driven signal transduction, but also the regulation of cellular growth. We have used a mutational approach to identify a gene, NPH4, that is necessary, not only for phototropism, but several additional differential growth responses as well. Not unexpectedly, given their pleiotropic phenotypes, null nph4 mutations also disrupt auxin responsiveness, both at the level of auxin-sensitive growth and auxin-induced gene expression. We have cloned the NPH4 gene via positional cloning and found that it encodes the auxin-reulated transcriptional activator ARF7. The Cholodny-Went theory holds that auxin becomes redistributed as a result of tropic stimulation and that resultant changes in local auxin concentrations lead to differential growth that is necessary for tropic curvatures. Given the information gathered through study of the NPH4 locus, it is now reasonable to hypothesize that the growth phase of phototropism is auxin-dependent because, at least in part, proteins necessary for localized growth are transcriptionally up-regulated in response to local changes in auxin concentration. We therefore propose to use microarray technology to identify genes whose expression patterns change in response to phototropic stimulation, in a NPH4-specific manner. In particular, we propose to compare gene expression profiles of wild-type seedlings to those of an isogenic nph4 mutant, after each has been exposed to a phototropic stimulation. Our control panels will be represented by the same genotypes, except that they will be mock-irradiated (represents the basal gene expression response). All changes in expression should therefore be specific to the phototropic stimulation and dependent upon the presence of the NPH4 protein. Verification of light-dependence will be accomplished by northern blot analysis of candidate genes in similarly treated nph1 null mutant seedlings lacking a phototropic photoreceptor. These microarray experiments complement display experiments currently underway in our laboratory. |
NASCArrays Information at The BAR
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