Biological nitrogen fixation in cereal crops Progress, strategies, and perspectives

Nitrogen is abundant in the atmosphere but is generally the most limiting nutrient for plants. The inability of many crop plants, such as cereals, to directly utilize freely available atmospheric nitrogen gas means that their growth and production often rely heavily on the application of chemical fertilizers, which leads to greenhouse gas emissions and the eutrophication of water. By contrast, legumes gain access to nitrogen through symbiotic association with rhizobia. These bacteria convert nitrogen gas into biologically available ammonia in nodules through a process termed symbiotic biological nitrogen fixation, which plays a deci-sive role in ecosystem functioning. Engineering cereal crops that can fix nitrogen like legumes or associate with nitrogen-fixing microbiomes could help to avoid the problems caused by the overuse of synthetic ni-trogen fertilizer. With the development of synthetic biology, various efforts have been undertaken with the aim of creating so-called N-self-fertilizingcrops capable of performing autonomous nitrogen fixation to avoid the need for chemical fertilizers. In this review, we briefly summarize the history and current status of engineering N-self-fertilizing crops. We also propose several potential biotechnological approaches for incorporating biological nitrogen fixation capacity into non-legume plants.

Automated summary

Nitrogen is a limiting nutrient for plants, and many crop plants rely on chemical fertilizers for growth due to their inability to directly utilize atmospheric nitrogen. Legumes, on the other hand, access nitrogen through symbiotic association with rhizobia. Engineering cereal crops to fix nitrogen or associate with nitrogen-fixing microbiomes could help reduce the reliance on chemical fertilizers. This review summarizes the history and current status of engineering N-self-fertilizing crops and proposes potential biotechnological approaches for incorporating biological nitrogen fixation capacity into non-legume plants.