Plant Protein Needs Adaptor to Promote Symbiosis with Fungi

Researchers Find Gene Activator Complex for Exchange of Nutrients Between Plants and Fungi

May 20, 2025

Most land plants form mutually beneficial symbioses with fungi. The plant and the fungus exchange vital nutrients. A team led by Prof. Dr. Caroline Gutjahr at the Max Planck Institute of Molecular Plant Physiology has uncovered a molecular mechanism that enables nutrient exchange between plants and fungi. Their findings offer promising insights into proteins that could support the design of crops with improved symbiotic nutrient intake to reduce artificial fertilizer inputs.

Arbuscules of the fungus Rhizophagus irregularis in a root of birdsfoot trifoil Lotus japonicus. In the wild type roots the arbuscules are fully developed and finely branched (left), while in the ram1 mutant, which is perturbed in the gene encoding the important transcription factor RAM1, they cannot fully develop and appear stunted (right). The fungus was stained with Wheat Germ Agglutinin coupled to AlexaFluor488. Size bar, 20 µM. — Arbuscules of the fungus *Rhizophagus irregularis* in a root of birdsfoot trifoil *Lotus japonicus*. In the wild type roots the arbuscules are fully developed and finely branched (left), while in the ram1 mutant, which is perturbed in the gene encoding the important transcription factor RAM1, they cannot fully develop and appear stunted (right). The fungus was stained with Wheat Germ Agglutinin coupled to AlexaFluor488. Size bar, 20 µM.

© Priya Pimprikar (Gutjahr Laboratory)

Arbuscules of the fungus *Rhizophagus irregularis* in a root of birdsfoot trifoil *Lotus japonicus*. In the wild type roots the arbuscules are fully developed and finely branched (left), while in the ram1 mutant, which is perturbed in the gene encoding the important transcription factor RAM1, they cannot fully develop and appear stunted (right). The fungus was stained with Wheat Germ Agglutinin coupled to AlexaFluor488. Size bar, 20 µM.

© Priya Pimprikar (Gutjahr Laboratory)

Most land plants collaborate with soil fungi in a symbiosis called arbuscular mycorrhiza. This symbiosis is one of the most widespread and ecologically significant plant-fungal partnerships and allows over 80% of land plants to improve nutrient uptake—particularly phosphorus—from the soil. In return the fungi receive energy-rich lipids from the plants.

At the centre of this nutrient exchange are so-called arbuscules. These are tree-shaped fungal structures inside root cortex cells, which release minerals such as phosphate to the plant cell and take up the plant-delivered lipids. They are surrounded by a plant membrane, which is full of transport proteins that channel the mineral nutrients or the lipids to the symbiotic partner.

The protein RAM1 has been known to be vital for the process of nutrient exchange between plants and fungi. This is a plant transcription factor – a protein, that switches on the activity and transcription of certain genes. When the genes are activated, they can provide templates for the production of particular proteins. Specifically, RAM1 is known to be essential for arbuscule development and necessary for the expression of a phosphate transporter gene and lipid biosynthesis genes essential for symbiotic nutrient exchange. It had remained unclear though how RAM1 could regulate gene expression because it cannot directly bind to DNA.

The Nutrient Exchange Gene Activation Decoded

Prof. Gutjahr's team, in collaboration with Dr. Nitzan Shabek’s group at the University of California, Davis, were now able to find out exactly how it works. Their research reveals that RAM1 forms complexes with WRI transcription factors, which act as DNA binding adaptors. This close physical interaction with a group of WRI-like DNA-binding proteins can control the activation of genes essential for nutrient exchange between plants and AM fungi during arbuscule formation.

“Our work offers a detailed view into the molecular control system that governs one of nature’s most beneficial partnerships,” says Caroline Gutjahr. “Understanding how these gene networks are coordinated opens new doors for improving crop nutrient efficiency without relying heavily on fertilizers.”

The discovery could contribute to future efforts in sustainable agriculture, including breeding or engineering crops that optimize symbiotic interactions. These could boost growth naturally with lesser use of chemical fertilizers that are harmful to the environment and drinking water.

Background info

The study was conducted in a collaboration with the group of Nitzan Shabek, expert in protein structure, at the University of California, Davis (USA). The lab of Prof. Dr. Caroline Gutjahr at the Max-Planck-Institute investigates the symbiosis between land plants and soil fungi. Arbuscular mycorrhiza is the key research field for the research group located in the Science Park in Potsdam.