Diurnal and Circadian Regulation of Protein Synthesis

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Protein synthesis is a fundamental activity of all cells and organisms, which consumes a substantial fraction of energy and metabolites. The growth of plants, in particular, is usually limited by the supply of nitrogen, and hence boosted by nitrogen fertilization. Most of the nitrogen needed by plants is needed for protein synthesis. The energy for protein synthesis is ultimately provided by sunlight, which is only available during the day. For these reasons, it is important to understand how protein synthesis is regulated over the day night cycle. This project will investigate how light stimuli and the internal circadian clock of the plant work together to ensure that the appropriate proteins are produced both during the day and at night. The project will also elaborate the cellular signal response mechanisms that allow plants to sense nutrient signals and regulate translation over the diurnal cycle. This work, to be performed in the reference species thale cress, will have implications for plant growth and development, and thus agricultural productivity, as well as the adaptation of plants to their natural environment. This project seeks to decipher how the alternation of day and night regulates protein synthesis (translation). Recent genome-wide studies from this and other laboratories have revealed that the translation of mRNA into protein is controlled jointly by the circadian clock and by light-dark transitions. The stage is now set to tackle two major scientific questions. First, how are environmental changes in the light-energy landscape integrated with the circadian clock to drive cycles of translation? This objective will be pursued by manipulating the light and nutrient environment in the context of the time of day and seasonal cues and by measuring the efficiency of mRNA ribosome loading. Mutant strains with defects in the clock and in light and nutrient sensing will be examined for alterations in the patterns of ribosome loading using gene-specific and genome-wide assays. Second, how do conserved eukaryotic regulatory pathways affect this form of translational control? Existing data have implicated the TOR kinase and GCN2 kinase pathways in translational control, but the precise contribution of these cellular signaling pathways to protein synthesis remain to be defined. Using genomics, molecular genetics, and computational systems-biology approaches, this research will enlighten the fundamental basis of an important constraint to plant growth, the regulation of protein synthesis by nutrient supply in a diurnal environment. This research will also develop the scientific workforce in an area of critical need. Among other training activities, the project will recruit middle or high school teachers from East Tennessee to create lesson plans and curricular materials that will familiarize underserved students with norms of science such as model-based inquiry and computational thinking.