Abstract
Iodine is a nutrient for mammals and brown algae. In humans, iodine is an important element by acting as a key component of the hormones produced by the thyroid gland. In contrast, iodine is not consensually considered a plant nutrient, yet plants are capable of absorbing and accumulating iodine, and its effect is broadly positive on plant growth and tolerance to environmental stress. For instance, iodine supplementation boosts antioxidant capacity and confers tolerance to salt stress. Surprisingly, our understanding of the uptake and mode‐of‐action of iodine at the plant molecular level is almost null. It is known that iodine is located mainly in the roots and partially translocated via xylem towards the shoots. In the shoots, it can be methylated by HTM enzymes (i.e. Arabidopsis HOL1), and then volatilized to the atmosphere as methyl‐iodide. Plant iodine content can thus be controlled by tuning the balance between uptake, accumulation and volatilization, opening a clear window for plant biotechnology strategies. Based on comparative genomics and transcriptomics, we were able to establish putative genes involved in specific iodine regulatory steps. In particular, we have been exploring HTMs as molecular tools to finetune internal iodine in Arabidopsis. We functionally characterized Arabidopsis HOL1 in response to increasing iodine supplementation and establish halide tolerance thresholds. Moreover, we studied the subcellular localization and expression patterns of AtHOL1 in the plant. Phylogenetic analysis indicated that HMTs are conserved in plants, with the exception of Fabaceae species. This result reinforces that HMTs can be a conserved strategy to modulate iodine, and possibly other halides, in plants. As a final goal, we intend to understand how iodine is regulated in plants to fully exploit iodine biological benefits and to develop iodine biofortified crops.