Science & Technology (Commonwealth Union) – Plants and the microbes around them compete for iron, and researchers at the Salk Institute have now identified a protein that settles that contest. The finding could eventually help in breeding hardier, more nutritious crops.
The study was published October 14 in the journal Science Advances.
A shared need for iron
Iron is essential to life. It helps cells produce energy, carries oxygen in our blood and supports the immune cells that fight infection. People get it through the food chain, which starts when plants draw iron out of the soil.
Iron is often scarce, and the shortage may worsen as weather and temperatures shift worldwide. Microbes living on and around plants want it too. Some invade plants to take iron from their cells, which forces the plants to defend themselves while protecting their own supply.
Wolfgang Busch, a Salk professor and a senior author of the study, said his team became interested in this struggle because plants and microbes are effectively fighting over a limited resource in the soil.
A protein that does two jobs
The team studied a protein called SRF3, which sits on the outer surface of plant cells and picks up signals from the environment. Busch and his colleague Matthieu Pierre Platre first linked SRF3 to plants’ responses to microbes in a 2022 study. That work also showed that SRF3 can sense iron levels and steer root growth accordingly. How it worked at the molecular level was unknown until now.
The researchers worked with Arabidopsis thaliana, a small flowering plant widely used in laboratories as a stand-in for crops such as wheat and corn. They tracked iron inside cells, followed the movement of SRF3 molecules and removed the protein entirely to see what happened.
They found a process with several steps. When SRF3 detects an invading microbe, it triggers the production of reactive oxygen species, molecules the plant uses to attack the intruder. That defense uses up the cell’s iron.
As iron falls, SRF3 changes position on the cell surface and is marked with a molecular tag called ubiquitin. The tag causes the cell to pull SRF3 inside. With the protein gone from the surface, production of the iron-draining molecules stops and balance returns.
In short, SRF3 starts the defense and also helps shut it down before the plant loses too much iron.
Reaching beyond a single protein
Platre, a former Salk staff scientist who is now at the Institute for Plant Sciences of Montpellier in France, said the study stands out because it explains the mechanism at every scale, from individual molecules up to the whole plant. He noted that this level of detail is rarely achieved in biology.
He also said the study is the first to show that ubiquitin tags, among the most widely used protein tags in cells, can rearrange proteins on a cell’s surface and change how the cell responds to its surroundings.
The researchers say the results support the idea that cell surfaces work like small computers, converting a flood of outside signals into actions. Platre noted that the idea was first proposed for mammalian cells and now appears to hold in plants as well. It may also be relevant to signaling proteins involved in cancer.
What comes next
Busch said the knowledge could someday guide the development of crops that resist disease, grow well and provide nutritious food, including under extreme weather and changing soil conditions. The work was done in a lab plant, and the researchers did not report any crop applications yet.
Next, the team plans to explore the cell-surface computing idea further and to identify other proteins and genes that SRF3 works with.
The research was funded by the National Institutes of Health, along with other public and private sources including the Human Frontier Science Program, the Helmsley Charitable Trust and the Chapman Foundation. Authors came from Salk and institutions in Spain, France, India and China.
