Plant nutrition is essential to understand any physiological process in plant biology, as well as to improve crops, and agricultural practices. The root microbiome plays an important role in plant nutrition. The best characterized microbiome elements are two plant endosymbionts: arbuscular mycorrhizal fungi (AMF) and rhizobia. AMF are responsible for delivering most of the mineral nutrients required by the host plant. Similarly, rhizobia in legume nodules provide the vast majority of the nitrogen requirements. Given their importance for plant nutrition a significant effort in understanding macronutrient exchange among the symbionts has been made. However, very little is known about metal micronutrient exchange.This is in contrast to the role of metals as essential nutrients for life (30-50 % of the proteins are metalloproteins) and to the yield-limiting effect that low soil metal bioavailability has worldwide. AMF are a source of metals, transferring the incorporated metals to the host,. Nitrogen-fixing rhizobia in mature nodules act as metal sinks, since the main enzymes required are highly expressed metalloproteins. We hypothesize that by changing the expression levels of the metal transporters involved, we will increase nitrogen fixation rates and increase plant metal uptake, resulting in higher crop production and fruit metal biofortification. Towards this goal, we will answer: i) How are metals incorporated from the AMF into the plant?, ii) How are metals delivered to the nodule?, iii) How are metals recovered from senescent nodules?, and iv) How does the natural variation of symbiotic-specific metal transporters affect yields and metal content of the fruit? In this project, we will use a multidisciplinary approach that involves metallotranscriptomics, plant physiology and molecular biology, and state-of-the art synchrotron based X-ray fluorescence to study metal distributions.