Understanding phytosiderophores’ role in crop improvement
When some grass crops such as wheat, barley and maize struggle to find enough micronutrients, they release metabolites known as phytosiderophores from their roots into the surrounding soil. These form a type of bond (stable complexes) with nutrients, making them soluble and available for uptake. The importance of phytosiderophores for plant iron nutrition has been known since the 1970s, but understanding their full role in plant-soil interactions has been challenging – mainly as these compounds aren’t commercially available. “Researchers couldn’t get the purified standards needed to measure them accurately or compare results across plants, soils or laboratories,” explains Eva Oburger(opens in new window), associate professor in the Institute of Soil Research at BOKU University. Through the PhytoTrace project, which was funded by the European Research Council(opens in new window) (ERC), Oburger and her colleagues from Vienna University of Technology(opens in new window) and the University of Vienna(opens in new window) sought to clarify the mechanisms underlying this micronutrient acquisition. The project used innovative soil-based and root sampling methods, along with advanced molecular techniques to investigate the phytosiderophore system in unprecedented detail. “The ERC funding enabled us to chemically synthesise all eight naturally occurring phytosiderophores in purified form,” notes Oburger. “This allowed us to develop a highly sensitive method that can detect and quantify all of them in natural samples, giving us for the first time the tools to ask and answer questions about how these compounds function and shape plant–https://www.nature.com/scitable/knowledge/library/the-rhizosphere-roots-soil-and-67500617/ (rhizosphere) interactions.”
Clarifying the role of phytosiderophores
The researchers started by adding or omitting individual micronutrients such as iron, zinc and copper independently in hydroponic experiments. Using barley as a model, the team measured phytosiderophore release under different micronutrient deficiencies, and monitored the activation of genes needed to produce them. After establishing these basic mechanisms, the researchers moved into more complex and realistic soil systems, tested the efficiency of different phytosiderophores, and gradually increased the genetic diversity of the studied plants.
Genetic variation in nutrient acquisition efficiency
One of the most striking findings was that phytosiderophores appear to have only a limited role in copper acquisition, despite the strong copper-phytosiderophore complexes formed in the soil solution. However, they found strong evidence that phytosiderophores contribute significantly to zinc acquisition. “This is particularly important because zinc deficiency is a major global challenge for both agriculture and human nutrition,” remarks Oburger. Another important finding was genotypic variation: some barley genotypes were much more efficient at acquiring micronutrients, and this was closely linked to how strongly the phytosiderophore pathway was activated. “This was very exciting because it showed that plants can differ substantially in how effectively they use these compounds under micronutrient-deficient conditions,” adds Oburger. “This variation is genetically controlled and heritable, which means it is something plant breeders can work with.”
Support for plant breeding
Indeed, the most direct implication of the findings is for plant breeding. “Because the phytosiderophore pathway is genetically controlled, it is entirely feasible to strengthen these traits through breeding and selection,” explains Oburger. Enhancing this natural mechanism offers a practical route to improving iron and zinc uptake under challenging soil conditions, which over the long term could help develop crops with higher micronutrient content, better growth and resilience in nutrient‑poor environments. “The next steps will include not only investigating other species, but also method development that will allow upscaling to bring this research closer to actual breeding practice,” says Oburger.
