Researchers discovered a zinc-sensing protein that regulates nitrogen fixation in legumes

A team of European scientists has identified a zinc-sensing protein that regulates nitrogen fixation in legumes, opening new possibilities for reducing synthetic fertilizer use in agriculture.

The protein, known as Fixation Under Nitrate (FUN), was found to act as a zinc sensor and transcription factor that influences how legumes interact with rhizobia bacteria to convert atmospheric nitrogen into a usable form for plant growth. The findings were published in Nature and are the result of a collaboration between researchers at Aarhus University, the Polytechnic University of Madrid, and the European Synchrotron Radiation Facility.

“Zinc has never before been considered a signaling molecule in plants,” said Assistant Professor Jieshun Lin of Aarhus University and lead author of the study. “After screening more than 150,000 plants, we identified FUN as a zinc-responsive regulator critical for nitrogen fixation.”

Legumes such as soybeans, cowpeas, and faba beans rely on symbiosis with nitrogen-fixing bacteria in root nodules. However, these nodules are highly sensitive to environmental conditions and often shut down when nitrogen is already abundant in the soil. The research shows that zinc acts as a secondary signal in this process, with FUN adjusting nodule activity based on cellular zinc levels. When zinc is plentiful, FUN becomes inactive by forming filaments; when zinc is scarce, it becomes active and promotes continued nitrogen fixation.

“This mechanism allows the plant to dynamically regulate nitrogen fixation in response to changing conditions,” said Professor Kasper Røjkjær Andersen, a co-author of the study. “That could be valuable in agricultural settings where minimizing fertilizer use is a priority.”

Sustained nitrogen fixation could increase nitrogen availability in soil, benefiting subsequent crops and reducing reliance on chemical inputs. The researchers plan to explore how this zinc signaling pathway can be applied to improve the efficiency and resilience of widely grown legumes.

The research was supported by the Enabling Nutrient Symbioses in Agriculture (ENSA) project, with funding from the Bill & Melinda Gates Foundation, the Carlsberg Foundation, and the European Research Council. A patent application covering the zinc signaling discovery has been filed by several members of the research team.