Collaborative Research: Multiple Approaches to Gain Increased Capture of Carbon Dioxide

植物捕捉阳光的能量，最初将二氧化碳和水转化为碳水化合物，然后最终转化为食物和纤维，供世界人口食用和穿衣。这一过程的一个主要问题是，将二氧化碳并入(或固定)到碳水化合物中的蛋白质--核酮糖二磷酸羧基酶/加氧酶(Rubisco)--效率低下。这是因为这种酶还将大气中的氧气固定到植物必须分解和回收的产品中。Rubisco对二氧化碳和氧气的这些固定过程是相互竞争的，而氧气的固定是如此之大，以至于植物捕获的30%以上的光能被浪费在这个过程中。该项目寻求通过增加Rubisco所在细胞内的二氧化碳浓度来最大限度地增加Rubisco固定的二氧化碳的数量(并将氧气的数量降至最低)。这将通过在植物细胞膜中引入一个光驱二氧化碳泵来实现，将二氧化碳从大气中转移到细胞中。这种泵将使用光合作用不需要的红外光作为其能源。在这个项目中，卤视紫红质将首先利用光能将氯离子转移到细胞内。然后，氯离子会移出细胞，并(通过一种称为逆向转运蛋白的膜蛋白的作用)交换进入细胞的碳酸氢根离子。然后，碳酸氢盐将被(一种名为脱水酶的酶)分解成二氧化碳和水，最终结果是二氧化碳通过光驱动过程被泵入细胞。在第二种方法中，计划重新设计卤视紫红质，将碳酸氢盐直接泵入细胞，而不使用氯离子作为中间体。更广泛的影响：本项目的目标是更有效地固定二氧化碳，预计作物产量将大幅增加。该项目产生的新技术将提供提高光合作用能力的工具和知识，这应该会迅速在农业和工业系统中应用。该项目还将包括为本科生和研究生以及博士后研究员提供密集的研究培训。

Plants capture the energy of sunlight to turn carbon dioxide and water initially into carbohydrates, and then eventually into food and fiber that feeds and clothes the world's population. A major problem with this process is that the protein that carries out the incorporation (or fixation) of carbon dioxide into carbohydrate, ribulose bisphosphate carboxylase/oxygenase (Rubisco), is inefficient. This is because this enzyme also fixes atmospheric oxygen into products that the plant must break down and recycle. These processes of fixation by Rubisco of carbon dioxide and oxygen are in competition, and the fixation of oxygen is so large that over 30% of the light energy captured by a plant is wasted in this process. This project seeks to maximize the amount of carbon dioxide (and minimize the amount of oxygen) fixed by Rubisco by increasing the concentration of carbon dioxide inside the cell, where Rubisco is located. This will be accomplished by introducing a light-driven carbon-dioxide pump into the plant cell membrane, to move carbon dioxide from the atmosphere into the cell. This pump will use infrared light, which is not required for photosynthesis, as its source of energy. In this project halorhodopsin will first move chloride ions into the cell, using the energy of light. The chloride ions will then move out of the cell and (through the action of a membrane protein called an antiporter) be exchanged for bicarbonate ions that move into the cell. The bicarbonate will then be decomposed (by an enzyme called anhydrase) into carbon dioxide and water, with the net result that carbon dioxide has been pumped into the cell by a light-driven process. In a second approach it is planned to re-engineer halorhodopsin to pump bicarbonate directly into the cell without using chloride ions as an intermediate. Broader Impacts: Large increases in crop yields can be expected from the more productive fixation of carbon dioxide that is the goal of this project. The new technologies derived from this project will provide tools and knowledge to boost photosynthetic capacity that should lead rapidly to applications in agricultural and industrial systems. The project will also include intensive research training for undergraduate and graduate students and for postdoctoral fellows.