Abstract:

Nitrogen is an essential element for plant growth and development. Legume plants form symbiotic relationships with rhizobia, which facilitates the biological fixation of atmospheric nitrogen (N₂) into ammonia (NH₃) that is directly usable by the plants through the action of rhizobial nitrogenase. This process reduces the need for chemical nitrogen fertilizers. However, under the pressure of continuously increasing food demand driven by a growing global population, the major non-leguminous food crops for humans, such as maize, rice and wheat, lack the ability to form nodules and establish symbiosis with rhizobia. This results in a heavy dependence on chemical nitrogen fertilizer to maintain high and stable yields. However, the overuse of chemical nitrogen fertilizers has caused serious environmental problems, including soil compaction and acidification, greenhouse gas emissions, and water eutrophication, all of which threaten agricultural sustainability and global food security. To achieve green and sustainable agricultural development and reduce the use of chemical fertilizers, nitrogen-fixing synthetic biology utilizes tools of synthetic biology to modify, optimize, and even de novo design biological nitrogen fixation systems. These engineered systems are applied across agricultural production, environmental protection, and industrial biotechnology, addressing global challenges such as excessive dependence on chemical nitrogen fertilizers, high energy consumption, and environmental pollution. The innovative strategies for bioengineering biological nitrogen fixation in non-leguminous crops can be categorized into the following four aspects. These strategies include engineering rhizobial nitrogen-fixing bacteria to increase nitrogen supply to the host, engineering crops to enhance the ability of plants to recruit nitrogen-fixing microbes in the rhizosphere to improve nitrogen use efficiency, forming nodule-like structures for symbiotic nitrogen fixation, and transferring functional nitrogenase components into plant cells to create self-fertilizing crops. Significant advances have been achieved in all these approaches in recent years, demonstrating their potential to boost yields while reducing fertilizers. This review provides a comprehensive overview of recent breakthroughs in nitrogen-fixing synthetic biology. We also discuss the current challenges and future prospects, offering theoretical insights and technical guidance to support further research and the practical application of biological nitrogen fixation in sustainable agriculture and environmental protection.

Key words: biological nitrogen fixation, synthetic biology, nitrogenase, non-leguminous crops, self-fertilizing crops

摘要：

自然界中，豆科植物可以通过与根瘤菌的共生，利用其固氮能力将空气中的氮气（N₂）还原为植物可直接利用的氨（NH₃），从而降低了豆科植物对化学氮肥的需求。然而，玉米和水稻等非豆科作物缺乏根瘤共生固氮的能力，其高产稳产严重依赖化学氮肥的施用。过量施用氮肥导致土壤板结酸化，温室气体排放及水体富营养化等严峻的环境问题，严重威胁农业可持续发展和粮食安全。本文综述了固氮合成生物学的研究历史与现状，为降低非豆科作物对化学氮肥的依赖，固氮合成生物学提出了多种策略：改造根际固氮菌以增强对宿主的氮素供给；增强作物根际招募有益固氮微生物的能力以提高氮素利用效率；工程化改造非豆科植物形成类根瘤器官实现共生固氮；或将固氮酶系统直接导入植物细胞以创制自主固氮作物。近年来，该领域在提升作物产量和部分替代化学氮肥方面已取得显著进展，推动了生物固氮技术在可持续农业与生态环境保护中的创新应用。本文最后对固氮合成生物学的未来发展方向进行了展望，旨在为相关研究提供理论参考与技术指导。

关键词: 生物固氮, 合成生物学, 固氮酶, 非豆科作物, 自主固氮作物