The nutrient molybdenum (Mo) is indispensable for nearly all known living organisms to accomplish important biological functions. Cells need to efficiently obtain and use Mo in order to ensure its presence in the active site of key enzymes such as nitrate reductase, sulfite oxidase, ARC, or nitrogenase. Mo is involved, among others, in nitrate assimilation, nitric oxide production, sulfite detoxification, or nitrogen fixation. However, little is known about Mo homeostasis in eukaryotic organisms. Nutrient homeostasis typically entails 1) strategies for nutrient uptake from soil, 2) nutrient storage, either by binding to other cell molecules, or by compartmentalization into cell organelles, 3) mechanisms for long-distance transport, to ensure nutrient supply to the whole plant, and 4) regulation mechanisms to coordinate intracellular nutrient content, environmental changes and cellular responses to those changes.

The unicellular green alga Chlamydomonas reinhardtii has been shown to be a good model to study Mo homeostasis since it has served to identify the first eukaryotic Mo uptake transporters.

Our goals are:

• Identify the molecular mechanisms used by eukaryotes to ensure cellular Mo availability.

• Use this knowledge to reduce nitrogen fertilizers in agriculture, either by optimizing plant inorganic nitrogen assimilation or by making possible nitrogen fixation in plants.

• Improve our knowledge about Mo metabolism and its implication in human diseases.