Genetic, Genomic, and Biochemical Approaches to Elucidate Control of Sulfur Deprivation Responses

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Sulfur is an essential element in proteins, lipids, and some critical metabolites. The work proposed in this grant continues an exploration of the regulatory aspects of sulfur deprivation responses in the alga Chlamydomonas. Regulatory mutants aberrant for sulfur-deprivation responses and suppressor strains will be characterized to help identify interactions among signaling factors. Wild-type and various mutant strains will be queried with genome-wide methods for examining the transcriptome under nutrient-replete and sulfur-starvation conditions, using both microarray and Solexa sequencing technologies. Focused intellectual and technical efforts will be directed toward establishing more biochemical links between identified regulators. A diversity of protein-protein interaction assays, including the yeast two-hybrid system, the split ubiquitin and split GFP systems and the classical co-immunoprecipitation assays will facilitate these studies, providing strong insights into the regulatory circuits that control nutrient limitation responses in photosynthetic organisms. Finally, analyses will be performed to help understand the two tiers of the sulfur-deprivation response that have recently been discovered; one is protein synthesis-independent while the other is protein synthesis-dependent. In a broader sense, the proposed work will help untangle some of the complexities associated with the regulatory machinery that is required for photosynthetic cells to cope with deprivation conditions and ultimately help us understand the impact of sulfur compounds in our diets and on global weather patterns; some sulfur compounds strongly influence the quality and nutritional value of food while others have profound effects on the climate of the Earth. The project will train a post doctoral student and will involve collaboration with Dr. Charles Hauser and his undergraduate students at St. Edward's University, who will participate in summer exchange and in the analysis of microarray results. St. Edward's University is a minority serving institution.