Regulatory Mechanisms of Metabolic Repression in Higher Plants

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The goal of this research project is to understand the regulatory mechanisms mediating metabolic repression of photosynthetic genes in higher plants. Recent studies in this laboratory have shown that sugars and acetate specifically and coordinately repress seven maize photosynthetic gene promoters. The repression is effective at physiological concentrations of these metabolites, and overrides regulation by light, cell type, and developmental stage. Metabolic repression of transcription appears to be a major regulatory circuit in maize and is susceptible to biochemical and molecular genetic analyses using protoplast transient expression methods established in this laboratory. The project can be divided into two parts: the first part is to continue the study of transcriptional mechanisms directly involved in glucose- and acetate-mediated photosynthetic gene repression. Using a well characterized maize photosynthetic gene promoter (the cabZm5 promoter) fused to an assayable reporter gene, the investigator will begin to define the cis-acting regulatory DNA elements mediating metabolic repression. The investigator will also characterize the changes in DNA-protein interactions which follow and/or mediate repression. The second part aims to understand how the glucose concentration is sensed and transduced. Various glucose analogues, chemical inhibitors, and maize hexokinase mutants will be used to determine whether glucose phosphorylation or metabolism is required for repression. Because preliminary results suggest cAMP can be a relevant second messenger in the maize system (as in yeast and vertebrates), the effects of agents impacting cAMP or cAMP-dependent protein kinases will be investigated. Finally, to test regulatory concepts generated by work using protoplast transient expression assays, the investigator will begin to create a transgenic maize system and analyze transgenic maize plants. The results from this project will provide much needed insight into metabolite-mediated signal transduction and gene regulation essential to plant growth and development.