Over the course of evolution, plants have developed an elegant strategy to counteract a lack of phosphate in the soil — they form symbiotic relationships with soil fungi. These mycorrhizal fungi efficiently supply their plant partners with phosphate and other essential minerals. Recently, scientists at the Leibniz Institute of Plant Biochemistry (IPB) in Halle, in collaboration with partners at the University of Bonn, discovered a molecular switch that detects the plant's phosphate content and signals whether to initiate or inhibit the symbiosis. This signaling pathway could enable plants to form partnerships with soil fungi even when sufficient phosphate is available. The study, published in the renowned journal Science Advances , offers a potential solution to a long-standing agricultural problem and opens new avenues for reducing fertilizer use.
Inoculating crops with mycorrhizal fungi is crucial for increasing agricultural yields. The fine fungal hyphae act like an extended root system, significantly increasing the uptake of minerals and nutrients. Phosphate is particularly vital for plants as it is a key regulator of their energy balance, and they efficiently extract it from the soil through this symbiosis. However, this partnership comes at a cost for plants: they must cede a portion of the carbohydrates they produce to the fungi. "This cost is so high for the plant that it suppresses the symbiosis when sufficient phosphate is available in the soil," explains Martina Ried-Lasi, head of the Symbiosis Signaling research group at the IPB. Despite an adequate phosphate supply, foregoing the symbiosis negatively impacts yields because the fungi also promote the uptake of nitrogen, magnesium, and potassium. "Therefore, agriculture is seeking strategies to maintain mycorrhizal associations in crops regardless of soil phosphate availability," says Gabriel Schaaf of the University of Bonn. "Our study demonstrates a potential approach for specifically promoting such symbioses in the future."
Using the model plant Lotus japonicus , the research team identified the enzyme VIH2 as a key regulator of symbiosis formation. VIH2 controls the production of inositol pyrophosphates, which are signal molecules that indicate phosphate status. When there is little phosphate in the cell, VIH2 produces low amounts of inositol pyrophosphates, signaling the cell to initiate a starvation program. This response includes activating phosphate-deficiency genes, remodeling root architecture, and initiating mycorrhizal symbiosis. When the phosphate supply is adequate, VIH2 produces large amounts of these signaling molecules. Accordingly, the phosphate starvation response is suppressed, and the partnership with mycorrhizal fungi is inhibited.
"We investigated whether a targeted inhibition of the enzyme would restart the phosphate starvation response and enable mycorrhiza formation," reports Martina Ried-Lasi. "And indeed, the plants behaved as if they were suffering from phosphate deficiency, even though sufficient phosphate was present in the culture medium." Consequently, the plants maintained their intensive colonization by mycorrhizal fungi, which are normally suppressed under the given phosphate conditions. The research team's most important finding: The sustained symbiosis had no negative effects on the growth and development of either partner under the experimental conditions studied. The fungal structures in the roots remained stable and functional, and the plants showed increased uptake of phosphate and other nutrients. "This allowed us to decouple the regulation of mycorrhizal symbiosis from the soil's phosphate status," says Gabriel Schaaf. "This has been a central goal in mycorrhiza research for decades."
With VIH2, plant experts have identified a key regulatory switch that controls the establishment of the symbiosis. This could enable the targeted manipulation of mycorrhization in crop plants in the future. Unlike conventional approaches, modern breeding methods such as genome editing can optimize the plant’s readiness for symbiosis flexibly and rapidly. However, it remains to be tested whether the effects on yield and stability can also be confirmed under field conditions. Nevertheless, this study introduces a new conceptual model that links phosphate perception in plants directly to the regulation of symbiotic relationships.
Phosphorus, in the form of phosphate, plays a central role in the energy metabolism of all living organisms. Phosphate is considered a limited, non-renewable resource. Additionally, many raw phosphate deposits are contaminated with heavy metals. Approximately 90 percent of the 200 million tons of raw phosphate mined worldwide each year is used to produce fertilizers. Without fertilizers, high-yield crop cultivation would not be possible. However, the excessive use of phosphate and mineral fertilizers leads to environmental problems such as soil contamination with heavy metals, groundwater pollution, and the eutrophication of aquatic ecosystems. Mycorrhization of crops is crucial for mitigating the phosphate problem in agriculture. With the help of these fungi in the soil, farmers can reduce their use of mineral fertilizers while lowering the risk of eutrophication.
Funding:
The work was funded by the German Research Foundation (DFG), including as part of the Transregio Collaborative Research Center TRR356 (IPB Halle) and the PhenoRob Cluster of Excellence at the University of Bonn.
Publication:
Raj, K., Gaugler, V. et al. Lotus japonicus VIH2 is an inositol pyrophosphate synthase that regulates arbuscular mycorrhiza. Science Advances (2026). https://doi.org/10.1126/sciadv.aec5607
Science Advances
Experimental study
Cells
Lotus japonicus VIH2 is an inositol pyrophosphate synthase that regulates arbuscular mycorrhiza.
22-May-2026