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

植物捕获阳光的能量，将二氧化碳和水最初转化为碳水化合物，然后最终转化为食物和纤维，为世界人口提供食物和衣服。这个过程的一个主要问题是，将二氧化碳结合（或固定）到碳水化合物中的蛋白质，二磷酸核酮糖羧化酶/加氧酶（Rubisco）效率低下。这是因为这种酶还能将大气中的氧气固定成植物必须分解和再循环的产物。Rubisco对二氧化碳和氧气的固定过程是相互竞争的，氧气的固定是如此之大，以至于植物捕获的30%以上的光能都浪费在这个过程中。该项目旨在通过增加Rubisco所在的细胞内二氧化碳的浓度来最大化Rubisco固定的二氧化碳量（并最小化氧气量）。这将通过将一个光驱动的二氧化碳泵引入植物细胞膜来实现，将二氧化碳从大气中转移到细胞中。该泵将使用红外光作为其能量来源，而红外光是光合作用所不需要的。在这个项目中，盐视紫红质首先利用光能将氯离子转移到细胞中。然后氯离子将移出细胞，并（通过一种称为反转运蛋白的膜蛋白的作用）与进入细胞的碳酸氢盐离子交换。然后，碳酸氢盐将被分解（通过一种叫做酸酐酶的酶）成二氧化碳和水，最终的结果是二氧化碳通过光驱动的过程被泵入细胞。在第二种方法中，计划重新设计盐视紫红质，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：通过更有效地固定二氧化碳，作物产量有望大幅增加，这是本项目的目标。从这个项目中获得的新技术将为提高光合作用能力提供工具和知识，这些工具和知识将迅速应用于农业和工业系统。该项目还将包括对本科生、研究生和博士后的强化研究培训。

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.