Résumé
Iodine is well known for its essential role in human nutrition. In plants, however, its function remains less explored. Even so, iodine is regarded as a beneficial element that, at appropriate concentrations, can enhance growth and improve tolerance to environmental stresses. When present in excessive amounts, whether through human activities or naturally occurring in certain ecosystems, iodine can become toxic to plants, a condition referred to as Reclamation Akagare disease. Maintaining a balanced internal iodine level is therefore crucial. To prevent toxicity, plants have evolved efficient mechanisms to regulate iodine content. One such mechanism is iodine volatilisation, carried out by halide methyltransferase (HMT) enzymes. These enzymes methylate iodide, enabling its release into the atmosphere. Consequently, HMTs play a key role in iodine homeostasis and are considered an important detoxification pathway in plants. In this study, we investigated the evolutionary conservation of the HMT gene family in plants. Phylogenetic analyses revealed that the family is highly conserved across plant lineages. To explore their functional roles, we generated Arabidopsis T-DNA insertion mutants, overexpression lines, and complementation lines, and exposed them to different concentrations of iodide salts. We assessed the resulting morphological and physiological changes and quantified iodine accumulation in each line, demonstrating a direct correlation between the presence of HMT and reduced iodine tolerance. Finally, our cross-species analysis showed that the absence of HMT is associated with increased iodine accumulation. Together, these findings provide a foundation for a deeper understanding of iodine regulation in plants and offer valuable perspectives for improving iodine tolerance and advancing biofortification strategies in crops.