Killing Two Birds With One Stone: Iron Biofortification as a Strategy for Enhancing Nutritional Value and Reducing Cadmium Accumulation in Rice Grain

Rice is a staple crop for nearly half of the global human population; however, it is typically low in iron (Fe) and accumulates high levels of cadmium (Cd) in grains when cultivated in Cd-polluted soils. Biofortifying rice with Fe nutrient while minimizing Cd levels is essential for improving human health. Fe deficiency could increase Cd uptake; conversely, Cd accumulation could induce Fe deficiency. Enhanced Fe supply could mitigate Cd accumulation under the influence of specific Cd─Fe interactions in the external environment and based on internal plant signalling activities. Here, we integrate current understanding of the Cd─Fe interaction mechanisms in paddy soils and rice plants. In paddy soils, Fe levels influence Cd bioavailability through adsorption, complexation and coprecipitation reactions, and water management influences the interactions between Fe oxides and Cd considerably. In plants, Fe competes with Cd for transporters, and Fe nutrition status can regulate the expression of key transporter genes involved in Cd uptake. We highlight Fe biofortification strategies in rice genetic breeding and agronomic practices for the achievement of low-Cd and high-Fe rice grain. This mini-review identifies knowledge gaps and strategies that could be prioritized to improve the nutritional value and safety of rice.