Engineering nitrogenase for plants and fungi – What is achieved and what remains?

Today, over 80% of the nitrogen in the average human body originates from industrial synthetic fertilizers used in agriculture. These are mainly produced by the Haber-Bosch process, in which H₂ and N₂ react over a catalyst at high temperature and pressure to generate ammonia (NH₃), a biologically active N species. Biological conversion of N₂ into NH₃, called nitrogen fixation, also exists in a group of bacteria, sometimes in association with plants of the legume family. In contrast, no plant, fungi or animal can fix nitrogen by itself. To reduce costs and negative effects on nature from large use of fertilizers, improving the ability of plants and plant-associated microorganisms to fix nitrogen has inspired plant biotechnologists for decades. Although considered an almost impossible task, recent advances in synthetic biology and genetics of nitrogen fixation has made this vision more realistic. In this review, we discuss strategies and advances towards engineering plants to express its own nitrogenase.