Researchers from Aarhus University have discovered a molecular switch that enables plants to enter into symbiosis with nitrogen-fixing bacteria, rather than fighting them. This breakthrough could pave the way for developing cereal crops capable of providing their own nitrogen, reducing agriculture’s reliance on synthetic fertilizers.

“We are moving closer to more sustainable and climate-friendly food production,” note the study’s authors, molecular biology professors Kasper Røjkjær Andersen and Simona Radutoiu.

Why Plants Need Nitrogen

Nitrogen is essential for plant growth, but most agricultural crops can only obtain it from fertilizers. Only a few plants, such as peas, clover, and beans, can thrive without additional nitrogen thanks to their symbiosis with certain bacteria that convert atmospheric nitrogen into a form plants can absorb.

Uncovering the Mechanisms of Natural Nitrogen Fixation

Scientists worldwide are striving to understand the genetic and molecular foundations of this ability. If these mechanisms can be introduced into staple crops like wheat, barley, and maize, these plants could become self-sufficient in nitrogen. This would significantly reduce the use of synthetic fertilizers, whose production accounts for about 2% of global energy consumption and is associated with substantial CO₂ emissions.

How Plants Choose Between Defense and Cooperation

Plants use receptors on their cell surfaces to detect chemical signals from soil microorganisms. Some bacteria release compounds that trigger a defensive response in plants, while others signal the potential for cooperation and nutrient exchange.

Legumes such as peas, beans, and clover allow specialized bacteria to enter their roots. Inside the root tissues, these bacteria convert atmospheric nitrogen and share it with the plant. This symbiosis enables legumes to grow without artificial fertilizers.

The Key Role of Two Amino Acids

The Aarhus University researchers found that the ability to form symbiosis is determined by just two amino acids in a root receptor protein. This protein decides whether to activate the plant’s immune system (defense) or to accept the bacteria (symbiosis). The team identified a segment of the protein, called Symbiosis Determinant 1, which acts as a switch controlling the plant’s internal signals.

By altering just two amino acids in this segment, the scientists were able to transform a receptor that normally triggers immunity into one that initiates symbiosis with nitrogen-fixing bacteria.

“We have shown that two small changes can make a plant switch its behavior—from rejecting bacteria to cooperating with them,” explains Simona Radutoiu.

Prospects for Major Crops

In laboratory experiments, the researchers successfully introduced this modification into the plant Lotus japonicus, and then tested the concept in barley—where the mechanism also worked.

“It’s amazing that we can now take a receptor from barley, make minor changes, and nitrogen fixation works again,” says Kasper Røjkjær Andersen.

The long-term potential is significant: if such modifications can be applied to other cereals, it may one day be possible to develop wheat, maize, or rice varieties capable of fixing nitrogen on their own, just like legumes.

“However, we still need to find other necessary keys,” notes Radutoiu.

“Today, only a few crops are capable of symbiosis. If we can extend this trait to widely grown crops, it could truly have a major impact on the amount of nitrogen used in agriculture,” the researchers conclude.