PI: Marinus Pilon Biology department, Colorado State University
Life as we know it is made possible by the process of photosynthesis, which is responsible for carbon fixation and thus biomass production. Photosynthesis in the green parts of plants takes place in specialized sub-cellular structures called chloroplasts. Chloroplasts contain the molecular machinery to use the energy of sunlight to drive a series of chemical reactions that include the production of carbohydrates (sugars) from water taken up by the plant roots and carbon dioxide from the air. To carry out its tasks the chloroplast needs specific redox active metal ions, particularly copper, iron and manganese. These ions are taken up from the soil and must be delivered to the chloroplasts. Copper delivery is the topic of this proposal. Although present in only very small amounts, copper is a very important metal ion for photosynthesis, and when its delivery to plastids is disturbed the plants can no longer grow. Copper ions are needed in two processes in photosynthesis: electron transport and photoprotection. When paired with the protein plastocyanin, copper is used in the conversion of light energy into chemical energy by means of electron transport. The enzyme superoxide dismutase is involved in photo-protection: it uses copper as a cofactor to protect the chloroplast from dangerous reactive oxygen species, which are formed as a by-product of photosynthetic electron transport, and thus indirectly the result of the action of plastocyanin. Thus, for optimal photosynthesis both plastocyanin and superoxide dismutase must obtain copper, yet both proteins compete for copper when the supply is limited, creating an interesting dilemma for how copper should be utilized. A set of proteins, including two chloroplast localized membrane transporters called PAA1 and PAA2, orchestrate the delivery of copper to chloroplasts. Exactly how this delivery machinery works and how it is regulated to allow the delivery of copper under varying conditions of copper supply is the topic of this project. The biochemical properties of copper delivery proteins will be analyzed, the effects of mutations in the genes encoding these proteins on growth and photosynthesis will be studied and their expression analyzed as a function of varying copper supply and demand. Models for the regulation of copper delivery will be tested by generating double mutations. Copper is a necessary component of the photosynthetic machinery and correct delivery is a prerequisite for enhanced crop yield and quality. Metal ions are also important for human health and nutrition. A better understanding of plant mechanisms involved in metal uptake, transport and homeostasis may lead to the development of crops with enhanced nutritional value. Apart from the significance to our understanding of biological processes this project will provide training and intellectual development opportunities for students both in the research lab and in the classroom. A postdoctoral researcher, two graduate students and several undergraduate students will take part in the proposed research project. The project involves collaboration with labs in the US and abroad, including personnel exchange and training opportunities.
