Metabolic engineering of the iodine content in Arabidopsis.
Bottom Line: In this work, we used a molecular approach to investigate how the ability of a plant to accumulate iodine can be influenced by different mechanisms.In particular, we demonstrated that the iodine content in Arabidopsis thaliana can be increased either by facilitating its uptake with the overexpression of the human sodium-iodide symporter (NIS) or through the reduction of its volatilization by knocking-out HOL-1, a halide methyltransferase.Our experiments show that the iodine content in plants results from a balance between intake and retention.
Plants are a poor source of iodine, an essential micronutrient for human health. Several attempts of iodine biofortification of crops have been carried out, but the scarce knowledge on the physiology of iodine in plants makes results often contradictory and not generalizable. In this work, we used a molecular approach to investigate how the ability of a plant to accumulate iodine can be influenced by different mechanisms. In particular, we demonstrated that the iodine content in Arabidopsis thaliana can be increased either by facilitating its uptake with the overexpression of the human sodium-iodide symporter (NIS) or through the reduction of its volatilization by knocking-out HOL-1, a halide methyltransferase. Our experiments show that the iodine content in plants results from a balance between intake and retention. A correct manipulation of this mechanism could improve iodine biofortification of crops and prevent the release of the ozone layer-threatening methyl iodide into the atmosphere.
No MeSH data available.
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Mentions: Since plant root transporters for iodine have not yet been isolated, we attempted to increase the iodine uptake of Arabidopsis thaliana plants by expressing the human sodium-iodide symporter (hNIS) protein under the control of the CaMV 35S promoter. Several independent transgenic lines were obtained with different levels of expression of the hNIS gene (Fig 1a). Line 16 was used for the experiments described in this paper, which were confirmed also by using line 17 (not shown). In NIS plants, hNIS expression was higher in roots than in leaves (Fig 1a). Radioactive 125I (approximately 0.3 pmol) were fed to wild type (WT) and NIS transgenic plants, which were kept at different temperatures. NIS plants accumulated more radioactive iodine, and this was particularly evident when plants were fed iodine at 30°C (Fig. 1b), a temperature that does not enhance the expression of hNIS (Fig. 1d) but is closer to the physiological environment of the human thyroid. At 37°C the plants suffered from heat stress, as demonstrated by the induction of HSP25.3, and this reduced the expression of hNIS (Fig. 1d). Iodine accumulated at a higher level in the young parts of the plant (Fig. 1c). Nitrate is an essential nutrient for plants, but can negatively affect the activity of NIS19. Increasing the nitrate level had a positive impact on the 125I uptake in WT plants, but decreased the iodine content in NIS plants (Fig. 1e), in line with its negative effect on the NIS transporter19. Because of the short duration of the treatment with high temperature or low nitrate, which were both limited to the iodine administration (approx. a week), no negative effects on plant growth were observed (data not shown). No differences related to the genotype were observed in the content of total nitrogen of the plants (Fig. 1g), indicating that the activity of NIS did not interfere with nitrogen metabolism. A positive effect of iodine feeding on nitrogen content was observed (Fig. 1g) and, although not relevant in the context of iodine biofortification, would be worthy of further study.
No MeSH data available.