When a plant has gotten enough nitrogen from the soil, it stops absorbing more. But how does it know when to quit? Scientists at New York University have found a key piece of the answer: a tiny protein called HHO5 that acts like a fullness sensor.
The discovery, published in the journal The Plant Cell, could help engineers create crops that grab more nitrogen from the ground. That matters because the world wastes a lot of fertilizer.
Plants today absorb only about half of the nitrogen farmers spread on fields, according to the NYU team. The rest washes away into rivers and lakes, where it can smother fish and trigger toxic algal blooms. Some unused nitrogen also escapes into the air as nitrous oxide, a greenhouse gas that traps heat 273 times more effectively than carbon dioxide over a century.
Making and shipping fertilizer is also expensive, and global supply chains face ongoing disruptions from geopolitical tensions.
"Improving the efficiency of fertilizer usage would have important environmental, economic and geopolitical impacts," said Gloria Coruzzi, a professor of biology at NYU who co-led the research.
To solve the problem, the researchers studied Arabidopsis thaliana, a small flowering plant often used in genetics research because it grows quickly and has a simple genome. They fed the plants different amounts and types of nitrogen, then tracked which genes switched on and off.
The team narrowed their search to HHO5, a protein that acts as a master switch for plant genes. When nitrogen levels are high enough, HHO5 ramps up production and tells the plant to stop pulling more nitrogen from the soil. It is essentially the plant's way of saying "I'm full."
"When organic nitrogen sufficiency triggers the HHO5 gene, HHO5 in turn signals for the plant to stop absorbing additional inorganic nitrogen from the soil, likely as a means of conserving energy," explained Will Hinckley, a doctoral student at NYU who led the study.
The finding opens a door for breeders and genetic engineers. If scientists can dial down HHO5's activity, they might create plants that keep slurping up nitrogen even after they would normally stop. Coruzzi called such hypothetical varieties "gluttonous" plants.
The research was a collaboration with Mariana Obertello at the Instituto de Investigaciones en Ingeniería Genética y Biología Molecular in Buenos Aires, Argentina.
The team is now investigating how HHO5 manages its double duty: turning on some genes while switching others off. Understanding that mechanism could help scientists fine-tune nitrogen use in crops like wheat, corn, and rice. If future studies pan out, farmers might one day grow the same amount of food with far less fertilizer, cutting costs and cleaning up waterways at the same time.