Plant molecule identified that boosts resistance to bacterial attacks, study flags

15 Jan 2024 --- While analyzing how plants manage iron deficiency, researchers from Salk Institute, US, found it eliminates IMA1, the molecular signal for iron shortfall in roots at risk of bacterial attack, while the same molecule can make leaves more resistant to these attacks. The research suggests that the iron deficiency signaling pathway and plant immune system are “deeply intertwined.”

The findings published in Nature provide a potential research target to improve plant resilience to climate change. The scientists used a hack to circumvent the aspect of the molecular process that allows the harmful bacteria to thrive.

“There is a long-established relationship between plant iron nutrition and bacteria. Exploring this relationship with more nuance allowed us to find a surprising new signaling pathway that plants use to turn off iron uptake as a defense strategy against threatening bacteria that also happens to alter the plant’s immune response,” says Wolfgang Busch, executive director of Salk’s Harnessing Plants Initiative and senior author of the study.

Iron is critical during host–microorganism interactions and restriction of available iron by the host during infection is an important defense strategy known as nutritional immunity.

Iron crucial in microbiome regulation
To unravel the complex relationship between plant health, iron levels and bacterial threat, the researchers used a small model plant called Arabidopsis thaliana, commonly known as Thale Cress. The scientists grew the plant in low-iron and high-iron growth soil, then added fragments of flagella — the little tails bacteria use to move — to mimic the presence of bacteria.

Plants and animals depend on iron for growth and microbiome regulation. The strategies plants use when increasing iron availability alter the root microbiome and can inadvertently benefit harmful bacteria in the soil. 

“Because bioavailable iron is a relatively scarce nutrient, iron deficiency — and consequential stunted plant growth — is common. Since stopping growth is not ideal, plants have developed techniques to encourage iron absorption in low-iron environments,” Busch explains. 

“Unfortunately, those techniques can alter the entire microbiome around the roots and increase iron availability for not just the plant, but for the harmful bacteria living nearby, too.”

The researchers hypothesized there would be competition between the plants and the bacteria for the iron. “But we found that when plants feel threatened by harmful bacteria, they are willing to stop acquiring iron and stop growing — they’ll deprive themselves in order to deprive the enemy,” says Min Cao, a postdoctoral researcher and first author of the study.Plant root cross-section showing iron deficiency signal IMA1 expression (Credit: Salk Institute). 

Instead of competing for the iron when the roots were exposed to flagella in low-iron environments, the plants forfeited the attempt by eliminating the iron-deficiency signal IMA1. When roots were exposed to flagella in high-iron environments, IMA1 was not eliminated and did not need to be expressed because the iron levels were sufficient.

Meanwhile, a recent study published in The Lancet Planetary Health found vitamin and mineral shortfalls in the EAT-Lancet planetary health diet. They are addressing concerns that the suggested diets are inadequate in iron, have nutritional gaps in four essential micronutrients and contain low amounts of nutritious animal-based foods.

Bacterial resistance and climate change
The more IMA1 the plants eliminated in response to low iron and flagella, the more resistant the leaves were to attacks from bacteria, demonstrating that iron availability and iron deficiency signaling are responsible for the plant’s immune response.

Learning about plant roots can teach scientists about other absorptive tissues, like the human gut, to better understand the intersection of mammalian microbiomes, immune systems and iron to improve health.

The gut microbiome is pegged as the “black box” of nutrition research as diet-microbiome interactions are anticipated to contribute to the foundation of dietary physiological effects. According to researchers from the University of Alberta, Canada and the University College Cork, Ireland, nutritional guidelines could be improved, modified and innovated based on data on diet-microbiome-host connections.

IMA1 has been identified as an essential target for optimizing plant immunity, which is becoming an increasingly more important issue as climate change and diseases evolve more quickly. The current finding is the beginning of plant resilience studies that link plant and animal microbiomes to climate change.

“Microbes determine the fate of carbon in soil, so uncovering how plants react to and impact their soil microenvironment can teach us a lot about optimizing plant carbon storage,” says Busch.

“Understanding how plants regulate signaling and immune responses in the face of environmental scarcities, like iron deficiencies, will be crucial as scientists optimize plant health in our continually changing climate.”

Future research will explore whether targeting IMA1 can change plant resistance to disease and how individual cells in plant roots shut down the IMA1 signaling pathway. 

By Inga de Jong