Rice Research Newton Fund: Exploiting a Cyanobacterial CO2 Concentrating Mechanism to Increase Photosynthesis and Yield in Rice

粮食安全被国际公认为是21世纪世纪的主要全球挑战之一。据预测，到2050年，世界粮食产量必须增加50%才能满足需求。这是对全球气候变化和资源限制的压力。迎接这一挑战将需要制定创新战略，以利用我们在后基因组时代前所未有的现代生物科学知识。水稻是人类最重要的食物，世界上一半以上的人口都在食用水稻，因此，开发高产水稻新品种是实现2050年目标的基础。虽然传统育种已使水稻产量大幅提高，但未来要实现大幅提高还需要新的方法。改善光合作用已被确定为用于提高C3作物植物产量的生物工程的主要目标。提高光合效率不仅增加了每公顷土地产生的碳水化合物的数量，而且还增加了每单位水和每单位氮的产量。这不仅意味着环境的可持续性，而且还意味着小农收入的增加和粮食安全的改善。固碳酶Rubisco（核酮糖-1：5-二磷酸羧化酶/加氧酶）的特性限制了陆地植物的光合作用效率。Rubisco催化RuBP（核酮糖-1，5-二磷酸盐）与CO2的结合，但也催化RuBP与氧气的反应，导致光呼吸，这是一个NH3和先前固定的CO2损失的过程。一些陆地植物（C4植物）和细菌已经进化出将CO2聚集在Rubisco附近的机制，从而增加光合作用的CO2同化，减少与氧气的竞争性浪费反应。然而，大米缺乏这种能力。因此，水稻利用的Rubisco酶具有更高的CO2亲和力，但比具有碳浓缩机制的植物（如玉米）中的Rubisco酶慢。因此，植物必须投入大量的蛋白质，从而氮，以允许Rubisco进行足够的碳固定，降低产量和生物质产量。根据已发表的模型，用一种更快的CO2特异性更低的酶取代内源性Rubisco，沿着碳浓缩机制（CCM），可以显着提高CO2固定，我们建议工程水稻的核基因组表达蓝藻β-羧基体的组分，包括更快的Rubisco酶。我们将鉴定具有所需水平的羧基体壳蛋白、内部蛋白和蓝藻Rubisco的转基因水稻品系，然后将其杂交以在同一品系中表达所有新蛋白。，我们将安装碳酸氢盐转运体的组合，以便向工程化的羧基体供应CO2。最后，我们还将通过RNA沉默技术降低叶绿体基质碳酸酐酶和内源水稻Rubisco的表达。基于模式植物烟草的有希望的结果，我们相信现在是时候开拓一个项目，将蓝藻CCM引入水稻的未来。

Food security is internationally recognised as one of the major global challenges of the 21st century. By 2050, it is predicted that world food production will have to increase by 50% to meet demand. This is against the pressures of global climate change and resource limitations. Meeting this challenge is going to require the development of innovative strategies to make use of our unprecedented knowledge of modern bioscience in the post genomic era. Since rice is the most important human food, consumed by more than half of the world's population, developing new highly-productive rice varieties will be fundamental to meeting the 2050 goal.Whilst substantial gains in rice yield have been obtained by traditional breeding, achievement of major increases in the future will require novel approaches. Improved photosynthesis has been identified as a major target for bioengineering for enhanced yield of C3 crop plants. Improving photosynthetic efficiency does not simply increase the amount of carbohydrate produced per hectare of land, but it also increases the amount produced per unit of water and per unit of nitrogen. This means not only environmental sustainability, but also higher income and better food security for small farmers.The properties of the carbon-fixing enzyme Rubisco (ribulose-1:5-bisphosphate carboxylase/oxygenase) are known to limit the efficiency of photosynthesis in land plants. Rubisco catalyses the combination of RuBP (ribulose-1,5-bisphophate) with CO2, but also catalyses the reaction of RuBP with oxygen, leading to photorespiration, a process in which NH3 and previously fixed CO2 are lost. Some land plants (C4 plants) and bacteria have evolved mechanisms that concentrate CO2 near Rubisco and thereby both increase photosynthetic CO2 assimilation and decrease the competing wasteful reaction with oxygen. However, rice lacks this ability. As a result, rice utilizes a Rubisco enzyme that has higher CO2 affinity but is slower than Rubisco enzymes in plants with carbon-concentrating mechanisms such as maize. Consequently, the plants must devote considerable amounts of protein, and thereby, nitrogen, to allow Rubisco to carry out adequate carbon fixation, reducing yield and biomass production. Replacing endogenous Rubisco with a faster enzyme with less CO2 specificity, along with a carbon concentrating mechanism (CCM), could significantly improve CO2 fixation, according to published models.We propose to engineer the nuclear genome of rice to express components of the cyanobacterial beta-carboxysome, including a faster Rubisco enzyme. We will identify transgenic lines of rice with the required levels of carboxysome shell proteins, internal proteins, and cyanobacterial Rubisco, which can then be crossed to express all of the novel proteins in the same line. , we will install a combination of bicarbonate transporters in order to supply CO2 to the engineered carboxysome. Finally we will also reduce the expression of the chloroplast stromal carbonic anhydrase and endogenous rice Rubisco through RNA silencing technology Based on promising results with the model plant tobacco, we believe it is time for forge ahead with a project that could bring the cyanobacterial CCM into rice for the future.