The mutually beneficial relationship between fungi and plants
From the plover that cleans the crocodile’s teeth to clownfish and anemones, nature is full of symbiotic relationships. But sometimes for this relationship to work, one of the involved parties must adapt. Take for example arbuscular mycorrhiza, a symbiosis between plants and fungi that is based on the mutual exchange of nutrients. “The fungus collects mineral nutrients from the soil and transports them directly into the plant’s root,” says Caroline Gutjahr, director of the Max Planck Institute of Molecular Plant Physiology. “In exchange, the fungus receives carbohydrates and lipids from the plant that it generated via photosynthetic carbon fixation.” Most of this exchange of nutrients happens via a highly branched and tree-shaped fungal structure, called an arbuscule, and the host plant cell. But, to allow the arbuscule to form, the host plant cell must internally reorganise itself, which it does using a step-by-step process. “In the first step, the cell forms a subcellular structure that lets the fungus enter and form a trunk,” explains Gutjahr. “Next, the arbuscule begins to develop branches before, after a few days of nutrient exchange, it collapses and disappears from the host cell.” While researchers know that this arrangement must be tightly regulated, the question is: How does this regulation happen? Helping to answer that question is the EU-funded RECEIVE project. “Transcription factors may drive arbuscule development by regulating genes, which become active in colonised cells in waves that drive different stages of development,” adds Gutjahr. “This project aimed to identify the transcription factors and their target genes that drive arbuscule development.” A transcription factor is a protein that controls when and how genes are turned on or off within a cell.
How the phosphate starvation response regulates arbuscular mycorrhiza
To start, the European Research Council supported project looked at the mycorrhizal roots that connect the fungus to the plant, with a specific focus on the waves of translation that happen during arbuscule development. “Not only were we able to better characterise proteins that were known to be present during the different stages of arbuscule development, we identified novel transcription factors involved in arbuscule development,” remarks Gutjahr. Researchers also found how arbuscular mycorrhiza is linked to the phosphate starvation response. While this response is key to helping plants adapt to phosphorus deficiency, researchers discovered that it also helps regulate arbuscular mycorrhiza. “This shows that arbuscular mycorrhiza is really part of the plant’s strategy to respond to phosphate starvation and is even co-regulated with other phosphate starvation responses using the same transcription factor,” notes Gutjahr. The details of this finding were published in ‘Nature Communications’.
New adventures in arbuscular mycorrhiza
In addition to solving the long-standing question of how plants regulate arbuscular mycorrhiza in response to phosphate status and to finding novel transcriptional regulators, the RECEIVE project developed new methods for studying arbuscular mycorrhiza in the laboratory setting. Researchers are already leveraging these methods to study which environmental conditions influence the action of the transcription factors regulating arbuscular mycorrhiza and by which molecular mechanism. “Our research has expanded our understanding of arbuscular mycorrhiza while also opening the door to exciting new experimental possibilities for our lab, which we will certainly pursue in the near future,” concludes Gutjahr.
Keywords
RECEIVE, arbuscular mycorrhiza, fungi, plants, symbiotic relationship, fungus, arbuscule, transcription factors, phosphate starvation
