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Increased sensitivity to iron deficiency in Arabidopsis thaliana overaccumulating nicotianamine.

Cassin G, Mari S, Curie C, Briat JF, Czernic P - J. Exp. Bot. (2009)

Bottom Line: Nevertheless, NA overaccumulation does not interfere with the iron uptake mechanisms since the iron levels are similar in the NA-overaccumulating line and wild-type plants in both roots and leaves under both sufficient and deficient conditions.However, NA overaccumulation triggers an enhanced sensitivity to iron starvation, associated with a decrease in iron availability.This study draws attention to a particular phenotype where NA in excess paradoxically leads to iron deficiency, probably because of an increase of the NA apoplastic pool sequestering iron.

View Article: PubMed Central - PubMed

Affiliation: Centre National de la Recherche Scientifique (UMR 5004), Institut National de la Recherche Agronomique, Université Montpellier 2, Ecole Nationale Supérieure d'Agronomie, 2 Place Viala, F-34060 Montpellier cedex 2, France.

ABSTRACT
Nicotianamine (NA) is a non-protein amino acid derivative synthesized from S-adenosyl L-methionine able to bind several metal ions such as iron, copper, manganese, zinc, or nickel. In plants, NA appears to be involved in iron availability and is essential for the plant to complete its biological cycle. In graminaceous plants, NA is also the precursor in the biosynthesis of phytosiderophores. Arabidopsis lines accumulating 4- and 100-fold more NA than wild-type plants were used in order to evaluate the impact of such an NA overaccumulation on iron homeostasis. The expression of iron-regulated genes including the IRT1/FRO2 iron uptake system is highly induced at the transcript level under both iron-sufficient and iron-deficient conditions. Nevertheless, NA overaccumulation does not interfere with the iron uptake mechanisms since the iron levels are similar in the NA-overaccumulating line and wild-type plants in both roots and leaves under both sufficient and deficient conditions. This observation also suggests that the translocation of iron from the root to the shoot is not affected in the NA-overaccumulating line. However, NA overaccumulation triggers an enhanced sensitivity to iron starvation, associated with a decrease in iron availability. This study draws attention to a particular phenotype where NA in excess paradoxically leads to iron deficiency, probably because of an increase of the NA apoplastic pool sequestering iron. This finding strengthens the notion that extracellular NA in the apoplast could be a major checkpoint to control plant iron homeostasis.

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Induction of iron uptake mechanisms in Arabidopsis lines overaccumulating NA. Wild-type plants (Columbia ecotype Col-0, black bars) and plants with a 4-fold (K8, grey bars) or a 100-fold (K1, white bars) increase in their NA content were sown on half-strength MS medium and after 5 d transferred to an iron-sufficient medium [50 μM Fe(III)-EDTA] for 12 d. Real-time RT-PCR determination of the relative transcript levels corresponding to the genes involved in the iron uptake, AtIRT1 and AtFRO2 (A), or in the transcriptional regulation of the iron starvation response, AtFIT1 (bHLH29), bHLH38, and bHLH39 (B). Error bars represent the SE of four repetitions. IRT1 protein accumulation in roots (C) was detected using an IRT1 affinity-purified peptide antibody (upper panel). The Coomassie staining shows equal loading (lower panel). Root Fe(III) chelate reductase activity (D) was performed on a mix of five plantlets. Error bars represent the SE of four repetitions.
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fig1: Induction of iron uptake mechanisms in Arabidopsis lines overaccumulating NA. Wild-type plants (Columbia ecotype Col-0, black bars) and plants with a 4-fold (K8, grey bars) or a 100-fold (K1, white bars) increase in their NA content were sown on half-strength MS medium and after 5 d transferred to an iron-sufficient medium [50 μM Fe(III)-EDTA] for 12 d. Real-time RT-PCR determination of the relative transcript levels corresponding to the genes involved in the iron uptake, AtIRT1 and AtFRO2 (A), or in the transcriptional regulation of the iron starvation response, AtFIT1 (bHLH29), bHLH38, and bHLH39 (B). Error bars represent the SE of four repetitions. IRT1 protein accumulation in roots (C) was detected using an IRT1 affinity-purified peptide antibody (upper panel). The Coomassie staining shows equal loading (lower panel). Root Fe(III) chelate reductase activity (D) was performed on a mix of five plantlets. Error bars represent the SE of four repetitions.

Mentions: In order to evaluate the role of NA in metal homeostasis, a T. caerulescens cDNA encoding NAS had been expressed in Arabidopsis. The resulting NA-overaccumulating lines were only characterized for heavy metal resistance, mainly Ni, and the phytoremediation process (Pianelli et al., 2005). However, the clear role of NA in iron homeostasis (see Introduction) prompted the analysis of the effect of a deregulation of the plant NA content on the expression of several well characterized target genes such as the root iron transporter AtIRT1 (Eide et al., 1996; Vert et al., 2002) and the root iron chelate reductase AtFRO2 (Robinson et al., 1999). Wild-type Col-0 and transgenic plants with a 4- or a 100-fold increased NA content (Pianelli et al., 2005), K8 and K1 lines, respectively, were grown in vitro under control conditions where iron is not limiting [50 μM Fe(III)-EDTA]. In wild-type Col-0 plants, the genes encoding the iron transporter AtIRT1 and the ferric reductase AtFRO2 were both expressed at a low level (Fig. 1A). In the NA-overaccumulating lines, however, expression of both genes was observed at higher levels (Fig. 1A). A 2-fold increase in AtIRT1 and AtFRO2 was observed in the K8 line, whereas their expression was 4- and 5-fold higher, respectively, in the K1 NA-overaccumulating line compared with the wild-type plants (Fig. 1A).


Increased sensitivity to iron deficiency in Arabidopsis thaliana overaccumulating nicotianamine.

Cassin G, Mari S, Curie C, Briat JF, Czernic P - J. Exp. Bot. (2009)

Induction of iron uptake mechanisms in Arabidopsis lines overaccumulating NA. Wild-type plants (Columbia ecotype Col-0, black bars) and plants with a 4-fold (K8, grey bars) or a 100-fold (K1, white bars) increase in their NA content were sown on half-strength MS medium and after 5 d transferred to an iron-sufficient medium [50 μM Fe(III)-EDTA] for 12 d. Real-time RT-PCR determination of the relative transcript levels corresponding to the genes involved in the iron uptake, AtIRT1 and AtFRO2 (A), or in the transcriptional regulation of the iron starvation response, AtFIT1 (bHLH29), bHLH38, and bHLH39 (B). Error bars represent the SE of four repetitions. IRT1 protein accumulation in roots (C) was detected using an IRT1 affinity-purified peptide antibody (upper panel). The Coomassie staining shows equal loading (lower panel). Root Fe(III) chelate reductase activity (D) was performed on a mix of five plantlets. Error bars represent the SE of four repetitions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2657549&req=5

fig1: Induction of iron uptake mechanisms in Arabidopsis lines overaccumulating NA. Wild-type plants (Columbia ecotype Col-0, black bars) and plants with a 4-fold (K8, grey bars) or a 100-fold (K1, white bars) increase in their NA content were sown on half-strength MS medium and after 5 d transferred to an iron-sufficient medium [50 μM Fe(III)-EDTA] for 12 d. Real-time RT-PCR determination of the relative transcript levels corresponding to the genes involved in the iron uptake, AtIRT1 and AtFRO2 (A), or in the transcriptional regulation of the iron starvation response, AtFIT1 (bHLH29), bHLH38, and bHLH39 (B). Error bars represent the SE of four repetitions. IRT1 protein accumulation in roots (C) was detected using an IRT1 affinity-purified peptide antibody (upper panel). The Coomassie staining shows equal loading (lower panel). Root Fe(III) chelate reductase activity (D) was performed on a mix of five plantlets. Error bars represent the SE of four repetitions.
Mentions: In order to evaluate the role of NA in metal homeostasis, a T. caerulescens cDNA encoding NAS had been expressed in Arabidopsis. The resulting NA-overaccumulating lines were only characterized for heavy metal resistance, mainly Ni, and the phytoremediation process (Pianelli et al., 2005). However, the clear role of NA in iron homeostasis (see Introduction) prompted the analysis of the effect of a deregulation of the plant NA content on the expression of several well characterized target genes such as the root iron transporter AtIRT1 (Eide et al., 1996; Vert et al., 2002) and the root iron chelate reductase AtFRO2 (Robinson et al., 1999). Wild-type Col-0 and transgenic plants with a 4- or a 100-fold increased NA content (Pianelli et al., 2005), K8 and K1 lines, respectively, were grown in vitro under control conditions where iron is not limiting [50 μM Fe(III)-EDTA]. In wild-type Col-0 plants, the genes encoding the iron transporter AtIRT1 and the ferric reductase AtFRO2 were both expressed at a low level (Fig. 1A). In the NA-overaccumulating lines, however, expression of both genes was observed at higher levels (Fig. 1A). A 2-fold increase in AtIRT1 and AtFRO2 was observed in the K8 line, whereas their expression was 4- and 5-fold higher, respectively, in the K1 NA-overaccumulating line compared with the wild-type plants (Fig. 1A).

Bottom Line: Nevertheless, NA overaccumulation does not interfere with the iron uptake mechanisms since the iron levels are similar in the NA-overaccumulating line and wild-type plants in both roots and leaves under both sufficient and deficient conditions.However, NA overaccumulation triggers an enhanced sensitivity to iron starvation, associated with a decrease in iron availability.This study draws attention to a particular phenotype where NA in excess paradoxically leads to iron deficiency, probably because of an increase of the NA apoplastic pool sequestering iron.

View Article: PubMed Central - PubMed

Affiliation: Centre National de la Recherche Scientifique (UMR 5004), Institut National de la Recherche Agronomique, Université Montpellier 2, Ecole Nationale Supérieure d'Agronomie, 2 Place Viala, F-34060 Montpellier cedex 2, France.

ABSTRACT
Nicotianamine (NA) is a non-protein amino acid derivative synthesized from S-adenosyl L-methionine able to bind several metal ions such as iron, copper, manganese, zinc, or nickel. In plants, NA appears to be involved in iron availability and is essential for the plant to complete its biological cycle. In graminaceous plants, NA is also the precursor in the biosynthesis of phytosiderophores. Arabidopsis lines accumulating 4- and 100-fold more NA than wild-type plants were used in order to evaluate the impact of such an NA overaccumulation on iron homeostasis. The expression of iron-regulated genes including the IRT1/FRO2 iron uptake system is highly induced at the transcript level under both iron-sufficient and iron-deficient conditions. Nevertheless, NA overaccumulation does not interfere with the iron uptake mechanisms since the iron levels are similar in the NA-overaccumulating line and wild-type plants in both roots and leaves under both sufficient and deficient conditions. This observation also suggests that the translocation of iron from the root to the shoot is not affected in the NA-overaccumulating line. However, NA overaccumulation triggers an enhanced sensitivity to iron starvation, associated with a decrease in iron availability. This study draws attention to a particular phenotype where NA in excess paradoxically leads to iron deficiency, probably because of an increase of the NA apoplastic pool sequestering iron. This finding strengthens the notion that extracellular NA in the apoplast could be a major checkpoint to control plant iron homeostasis.

Show MeSH
Related in: MedlinePlus