A team of researchers from the University of Oxford, UK, have managed to give cereals the ability to control the bacterial process of nitrogen fixation, according to a study published in Proceedings of the National Academy of Sciences.
Most of our food supplies come from cereals, including wheat, maize, barley, and rice. However, these crops need to receive substantial amounts of nitrogen fertiliser, usually in the form of ammonia. This type of fertiliser is commonly used in agriculture, and since the early 20th century, it has been provided by industrially produced ammonia. While it dramatically increases production, it also negatively impacts the environment through pollution and greenhouse gas emissions.
In contrast, legumes have the ability to develop nodules on their roots full of bacteria called rhizobia. These bacteria can take nitrogen from the air and turn it into ammonia fertiliser for the plants. It’s long been a dream of researchers in this field to add this ability to fix nitrogen to cereals to reduce the need for ammonia fertiliser.
Now, researchers from Oxford University, in collaboration with the University of Cambridge and the Massachusetts Institute of Technology (MIT), are one step closer to making cereals have their own ability to obtain nitrogen from bacteria in their roots.
The team developed a kind of barley that can produce a signal molecule called rhizopine that regulates the genes in the rhizobia bacteria growing in the roots. Plants secreting rhizopine can actually control nitrogen fixation by the bacteria in their roots. Bacteria only fix and release nitrogen on barley plants with the rhizopine signal and not on any other plants.
This work is an incredible milestone towards developing a synthetic version of the symbiosis between plant and bacteria, where bacteria fix nitrogen for the desired host plant but not for non-host plants, such as weeds. With this system, plants can switch on nitrogen fixation to get the ammonia they need.
“Biological nitrogen fixation is one of the key processes enabling more sustainable agricultural practices and has been the subject of extensive research efforts for decades. This work on developing plant control of bacterial nitrogen fixation is a key part of a large effort to transfer root nodulation and nitrogen fixation to cereals. This was only made possible through a great collaborative effort bringing together the work done by multiple labs over many years,” said Professor Philip Poole, from the Department of Biology, at the University of Oxford.
Haskett T, Paramasivan P, Mendes M et al. (2022) Engineered plant control of associative nitrogen fixation. PNAS, https://doi.org/10.1073/pnas.2117465119