“We are one step closer to a greener and climate-friendlier food production.”
That is the conclusion of Kasper Røjkjær Andersen and Simona Radutoiu, professors of molecular biology at Aarhus University, who have led a new study uncovering a key mechanism that could help reduce agriculture’s dependence on artificial fertilizers.
Plants require nitrogen to grow, yet most crops can only obtain it through fertilizers. A few species — such as peas, clover, and beans — can thrive without them because they form a symbiotic relationship with specialized bacteria that convert atmospheric nitrogen into a form the plants can use.
Around the world, scientists are working to understand the genetic and molecular basis of this natural nitrogen fixation, with the goal of one day transferring the ability to major cereal crops like wheat, barley, and maize. Achieving this would make these plants self-sufficient in nitrogen, dramatically lowering the need for synthetic fertilizers—currently responsible for about two percent of global energy use and significant CO₂ emissions.
The Aarhus University team identified subtle changes in plant receptors that cause them to suppress their immune system, allowing nitrogen-fixing bacteria to establish a symbiotic relationship.
Friend or Foe?
Plants rely on receptors on their cell surfaces to detect signals from soil microorganisms. Some bacteria release chemical cues that trigger plant defenses, identifying themselves as potential threats. Others signal cooperation, offering nutrients in exchange for a safe habitat.
Legumes such as peas, beans, and clover are especially adept at this — they welcome specific bacteria into their roots, where the microbes convert nitrogen from the air into a usable form. This symbiosis enables legumes to grow without artificial fertilizers.
The researchers found that this remarkable ability depends largely on two amino acids, tiny molecular “building blocks” within a root protein, which play a decisive role in determining whether a plant perceives bacteria as a friend or foe.
“This is a remarkable and important finding,” Radutoiu points out.
The researchers identified a small region in the protein, which they named Symbiosis Determinant 1 — a molecular switch that dictates the signal transmitted within the plant cell.
By altering just two amino acids in this region, they were able to reprogram a receptor that typically activates the plant’s immune response, enabling it instead to initiate symbiosis with nitrogen-fixing bacteria.
The protein in the roots functions as a “receptor” that receives signals from the bacteria. It decides whether the plant should sound the alarm (immune system) or welcome the bacteria (symbiosis).
“We have shown that two small changes can cause plants to alter their behavior on a crucial point — from rejecting bacteria to cooperating with them,” Radutoiu explains.
Possible in Wheat, Barley, and Maize?
In the laboratory the researchers successfully modified the plant Lotus japonicus. But the same principle proved to apply in barley, according to a press release.
“It is quite remarkable that we are now able to take a receptor from barley, make small changes in it, and then nitrogen fixation works again,” says Kasper Røjkjær Andersen.
And the perspectives are big. If the modification can be transferred to other crops, eventually it may be possible to breed cereal plants such as wheat, maize, or rice with the ability to fix nitrogen themselves — just as legumes do today.
“But we have to find the other, essential keys first,” says Simona Radutoiu, adding:
“Only very few crops can perform symbiosis today. If we can extend that to widely used crops, it can really make a big difference on how much nitrogen needs to be used.”
