Cereals take control of bacterial production of ammonia fertiliser

New research from the University of Oxford, in collaboration with the University of Cambridge and the Massachusetts Institute of Technology (MIT), has established control of bacterial nitrogen fixation by cereals.

Researchers have made a major breakthrough in establishing the ability of cereals, such as barley, wheat, maize and rice, to make their own nitrogen fertiliser in the form of ammonia.

Most of our food supply comes from cereals such as barley, wheat, maize and rice. These need to be given large quantities of industrially produced ammonia fertiliser to drive high yields.

Ammonia-based fertiliser is commonly used in industrial agriculture, and since the early 20^th Century this has been provided by industrially produced ammonia. Whilst this does increase crop yields, it has had a catastrophic impact on the environment through pollution and greenhouse gas emissions.

Legumes have been used in farming for thousands of years because of their ability to develop nodules on their roots which house bacteria called rhizobia. The rhizobia take nitrogen from the air and turn it into ammonia fertiliser for the plants.

A dream of farmers, agronomists and scientists is to transfer the ability to fix nitrogen from legumes to the cereals.

But how can this process be controlled? In the research, led by Dr Timothy Haskett and Professor Philip Poole, Department of Biology, University of Oxford with collaborators at the University of Cambridge and MIT, the question has been answered.

The researchers developed a kind of barley that produces a signal molecule called rhizopine that controls the genes in the rhizobia bacteria growing on the plant's roots. They showed that plants secreting rhizopine controlled nitrogen fixation by the bacterium on its roots. The bacteria would only fix nitrogen on the barley which released rhizopine and not on any other plant.

This work is a key milestone towards the development of a synthetic plant-controlled symbiosis in which the bacteria fix nitrogen only when in contact with the desired host plant and not on the roots of nonhost plants, such as weeds. It will enable plants to switch on nitrogen fixation by bacteria and release the product ammonia to provide fertiliser to the plant.

Professor Poole said:

'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.'

To read more about this research, published in PNAS, please visit: https://doi.org/10.1073/pnas.2117465119