Abstract:

Reducing carbon emissions is a major strategic decision in the process of sustainable development in China. In order to achieve the ambitious goal of “carbon peak， carbon neutrality” on schedule, China needs to make a breakthrough in improving the ecological carbon sink capacity. Plant photosynthesis is beneficial to increase the Earth's carbon sink by fixing atmospheric carbon dioxide or inorganic carbon to produce organic compounds, while CO₂ is released in the process of photorespiration and respiration which reduce carbon sinks by degrading the organic compounds into other substrates. Energy utilization rate of the above-mentioned CO₂ natural metabolic process is low, and those processes are difficult to be artificially modified and improved in plants due to the characters and limitations of the relevant enzymes. Therefore, reconstructing new artificial metabolic pathways with synthetic biology in plants is expected to greatly improve the plant CO₂ fixation capacity, which is one of the effective ways to solve the bottleneck of humanity development in the future. In the present review, we introduce the metabolic pathways associated with CO₂ fixation and release which are involved in plant photosynthesis, photorespiration and respiration, respectively, and then point out the potential targets that could be used for modification by synthetic biology. In each section, we mainly discuss the artificial carbon fixation pathways that have been implemented in plants and their underlying principles. Especially, the modification of photorespiration is particularly discussed and several pathways are mentioned in details which shed lights on the design of artificial pathway in the future. Then we compare the capacity of each pathway in carbon fixation and limitation. Finally, we propose the key questions of designing and synthesizing novel carbon fixation pathway in plants, and the zero-carbon releasing design is mainly discussed. The development trend of transformation of plant CO₂ metabolic pathway by synthetic biology is also forecasted.

Key words: plant, CO₂ metabolism, synthetic biology, modification, synthetic biology, carbon neutrality

摘要：

降碳减排是我国可持续发展过程中的一项重大战略决策。为如期实现“碳达峰、碳中和”宏伟目标，我国需在提高生态碳汇能力上取得突破。植物光合作用有利于增加地球碳汇，而光呼吸和呼吸作用过程则释放CO₂。自然状态下，上述CO₂代谢过程能量利用率低、人工改造并提高植物CO₂固定的难度较大。因此，在植物体内重构新的人工代谢途径，有望大幅提高植物CO₂固定能力，是解决人类社会发展瓶颈的有效途径之一。本文分别介绍了植物光合作用、光呼吸和呼吸作用中与CO₂固定、释放相关途径，并指出可用于改造的潜在靶点；重点综述了植物体内已构建的人工固碳途径及其代谢原理，系统分析评价了不同途径的CO₂固定能力和限制因素；最后，对人工设计及合成植物CO₂代谢通路、基于零碳排放的新型物质生产等关键问题进行了探讨，并对植物CO₂代谢途径的改造发展趋势进行了展望。

关键词: 植物, CO₂代谢, 改造, 合成生物学, 碳中和