The iodine physiology in plants: physiological and molecular mechanisms responsible for the iodine uptake in plants and strategies for crop iodine fortification

Iodine is an essential element in human diet and strategies for food iodine fortification are being developed. Iodine physiology in plants is largely unknown. The aim of this work is expand our knowledge on the physiology of this element in plants, also to increase iodine content in crops. Two strategies have been developed, taking advantage of an A. thaliana T-DNA mutant for the Hol1 (Harmless to Ozone Layer) gene, involved in the iodine volatilisation as methyl halide, and an A. thaliana transgenic line over-expressing the human Na-I symporter (NIS, Sodium Iodide Symporter). The cross between hol1 mutant and NIS over-expressing plants was also performed. The results suggest that Hol1 gene expression is induced by iodine fed to the medium and its expression correlates with the amount of iodine taken up by the plants. Furthermore, using radioactive iodine and ICP-MS analysis it was observed that both in the hol1 mutant and in NIS over-expressing plants iodine uptake is enhanced. Moreover, in the hol1 mutant the amount of iodine accumulated after 4d of KI treatment is 114 mg/Kg (FW), 5 higher than in wild type. However, the highest iodine concentrations were found in NIS x hol1 plants, suggesting that both enhancing iodine uptake and stopping iodine volatilisation are effective strategies for fortifying crops. The results obtained in A. thaliana were then also applied in tomato plants (cv MicroTom) to evaluate the possibility of increasing the iodine content in fruits. We found that tomato plants can tolerate high levels of iodine, stored both in vegetative tissues and fruits in concentrations that are more than enough for the human requirements.