Copper is an essential cofactor for plant growth due to its essential role in photosynthesis. When copper uptake is not sufficient, plants use a combination of three strategies to adjust: Plants modify their physiology to reduce their need for copper, they attempt to increase copper uptake, and they prioritize delivery of copper to the most essential proteins, especially those that function in photosynthesis. The team has already discovered key copper-transporter molecules and has found that a class of small RNA molecules called microRNAs function in the regulation of the use of copper. In this project the investigators aim to characterize how the components that were identified work together in order to adjust to impending copper deficiency. For this project a combination of genetic and biochemical approaches will be used in the model plant Arabidopsis thaliana. The project will likely reveal important novel mechanisms by which organisms adjust to micro-nutrient deficiency. Copper deficiency affects crop yield and biomass production, which has an impact on the possibility to make biofuels. Deficiency also affects the nutritional value of edible plant parts. Therefore the project has relevance to the well being of humans. The project will train graduate students as well as undergraduates and post-doctoral researchers and will involve national and international collaborations. Many of the discoveries in biochemistry that have led to improvements in human health and well being have arisen from research in the area of plant science. In order to raise awareness of the importance of basic plant science, the research team will organize workshops aimed primarily at teachers and local farmers around the themes of nutrition and plants, photosynthesis and biofuels and plant research from genomics to ecophysiology.

Project Report

PI: Marinus Pilon, Colorado State University, Fort Collins, CO Intellectual merit and broader impacts. Living organism catalyze chemical reactions using enzymes. Roughly a third of all enzymes require a metal ion as cofactor for activity. In natural and agricultural soils, plant productivity can be severely limited by nutrient deficiency. Photosynthesis is the process required for all biomass formation and it drives all life on our planet. It is important for the future of sustainable practices to understand which factors limit photosynthetic productivity. Micronutrients are an important part of this picture and copper turns out to be one of the most interesting elements in this context. Copper deficiency in plants leads to defects in photosynthesis, chlorosis or reduced greening and wilting of leaves. Copper is not considered a "mobile" element. This means that under impending deficiency, copper is not easily mobilized to newly developing leaves from older tissue. Deficiency of copper can affect both the quality and quantity of edible plant parts, thereby affecting a large portion of the world’s population for whom plants serve as the major source of food. It is therefore very important to understand how plants manage the uptake, distribution and delivery of essential micronutrients such as copper. In this project, we have used Arabidopsis thaliana (mouse ear cress) as a model plant system to study copper delivery to plastids, which are the site of photosynthesis. The regulation of copper delivery to the plastids has emerged as a very interesting model for micro-nutrient distribution in complex eukaryotic systems. We have first studied the function and regulation of two copper-transporting proteins that serve to deliver copper to the photosynthetic machinery. We have found that one of these transporters is regulated by specific degradation in the presence of excess copper. This mechanism serves to fine tune the delivery of copper ions to the various compartments within the cell. This process involves a novel copper sensing mechanism. We have also studied how the two copper transporters are targeted within the plant cell. For this purpose we have expressed fusions of the transporters with green fluorescent protein. Analysis by confocal fluorescence microscopy revealed an important role for the amino-terminal extensions of the two transporters in the insertion into the correct sub-cellular membranes. Plants can thrive on soils that vary widely in copper content. We had postulated before that a set of small RNA molecules, called the copper microRNAs, are important to the capacity of the plant to economize copper cofactor use. The copper microRNAs (which are highly conserved in plants) serve to down-regulate the expression of apparently redundant copper proteins. We found that not only the copper binding proteins themselves but also copper delivery factors are down regulated by this mechanism, revealing exceptional coordination and fine tuning of copper delivery systems. Using controlled feeding experiments and a temporal analysis we were able to show that photosynthetic and respiratory functions are indeed prioritized when it comes to copper cofactor delivery especially in young developing leaves. The results of these studies were disseminated by publication in leading scientific journals and by presentations at international meetings. Seeds of produced plant lines have been sent to the ABRC seed collection for use by the plant science community. In the context of this project the PI has developed a graduate course in Plant Metabolism (with emphasis on photosynthesis), which includes practical - in the lab - training in measuring photosynthesis parameters (given in 2008 and 2010 and again in 2012, total enrollment of 22 students). The PI has given two presentations for industry representatives interested in biofuels. Three graduate students have been trained in the project and one post-doctoral fellow. Graduated Ph.D. students have found immediate employment after graduation, for instance as senior scientist in an algal biofuels company. In addition, several CSU undergraduates have received research experience and training. The lab hosted undergraduates students partially funded by the C2B2 (Colorado Center for Bio-fuels and Bio-refining) full time in the summers of 2010 and 2011.

National Science Foundation (NSF)
Division of Integrative Organismal Systems (IOS)
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Steven Ellis
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Colorado State University-Fort Collins
Fort Collins
United States
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