Integrating Cellular Iron Compartmentalization Mechanisms

The World Health Organization (WHO) estimates that more than 2 billion people suffer from iron (Fe) deficiency due to inadequate intake of dietary Fe. The majority of these people obtain their Fe primarily from plant-based diets, which tend to have low levels of bioavailable Fe. In addition, approximately 30% of the world's soils are Fe deficient, resulting in significantly reduced crop yields. Fe is essential for both photosynthesis and respiration, yet we do not know how Fe is delivered to the compartments in which these essential processes are located (chloroplasts and mitochondria, respectively). This project is designed to produce fundamental knowledge concerning the delivery of Fe to these subcellular compartments and enable development of higher-yielding, more nutritious crop plants. This project will include outreach activities in local public primary schools that focus on the importance of plants to humans and the effects of environmental stressors on plant growth and productivity.

Iron (Fe) is an essential nutrient for plants where it plays essential roles in the electron transport chains of photosynthesis and respiration. Although much progress has been made in recent years regarding the mechanisms involved in Fe uptake from the soil, current understanding of subcellular trafficking of Fe, particularly trafficking to and from the mitochondria and chloroplasts, is poor. In addition, the mechanisms that control organellar Fe homeostasis and sensing remain unknown. This project builds upon the PIs previous studies of ferric chelate reductases (FROs) that appear to function in mitochondrial and chloroplast Fe trafficking and homeostasis as well as mitochondrial Fe transporters (MITs) that appear to be responsible for movement of Fe into mitochondria. The central hypotheses of the project are that organellar FROs and MITs play critical roles in compartmentalization of Fe, and compartmentalization of Fe, in turn, modulates whole plant Fe metabolism. In this project, the physiological roles of mitochondrial FROs and MITs will be investigated via analysis of Arabidopsis loss-of-function lines (Aim 1). The precise suborganellar localization and membrane topology of organellar FROs will be investigated using fractionation and self-assembling split GFP approaches (Aim 2). Finally, the mechanisms involved in Fe compartmentalization and Fe sensing by mitochondria and chloroplasts will be investigated via analysis of changes in Fe compartmentalization patterns and transcriptional profiles of lines with reduced chloroplast (fro7) and mitochondrial (fro3) Fe content (Aim 3). Thus, this project will generate important new insight into the molecular mechanisms underpinning Fe trafficking and accumulation in plants.