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Planta

, Volume 226, Issue 4, pp 897–908 | Cite as

Iron deficiency-mediated stress regulation of four subgroup Ib BHLH genes in Arabidopsis thaliana

  • Hong-Yu Wang
  • Marco Klatte
  • Marc Jakoby
  • Helmut Bäumlein
  • Bernd Weisshaar
  • Petra BauerEmail author
Original Article

Abstract

Networks of transcription factors control physiological, developmental and environmental responses. Root iron acquisition responses are controlled by the essential bHLH protein FIT. Recently, two group Ib BHLH genes were reported to be iron deficiency-regulated. Here, we studied expression patterns of these two group Ib BHLH genes and of their two closest homologs to analyze whether their regulation would support a function in iron deficiency responses. We found that BHLH038, BHLH039, BHLH100 and BHLH101 (comprising a subgroup of BHLH Ib genes) were up regulated by iron deficiency in roots and leaves. Single insertion mutants had no visible phenotype and were capable of inducing root iron acquisition responses, presumably due to functional redundancy. Specific metal treatments like nickel, high zinc or high copper resulted in induction of the four BHLH Ib genes whereas high iron, low copper and low zinc repressed gene expression. Induction of the four BHLH Ib genes was also found in multiple iron acquisition mutants including fit. Ectopic activation of FIT did not suppress the four BHLH Ib genes. Split-root analyses using promoter-GUS lines showed that FIT and BHLH100 promoters were controlled by different local and systemic signals involved in their regulation by iron. These results indicated that the four BHLH Ib genes were induced independently from FIT by conditions causing iron deficiency. Taken together, BHLH038, BHLH039, BHLH100 and BHLH101 function differently from FIT and may be involved in mediating a signal related to iron deficiency-induced stress and/or internal iron homeostasis.

Keywords

bHLH Basic helix-loop-helix Fer-like iron-deficiency induced transcription factor (FIT) Iron acquisition Iron uptake Split root Transcription factor 

Abbreviations

bHLH

Basic helix-loop-helix

FIT

Fer-like iron-deficiency induced transcription factor

FIT1

Fe-deficiency induced transcription factor

MU

4-Methylumbeliferyl-β-D-glucuronide

qRT-PCR

Quantitative reverse transcription PCR

Notes

Acknowledgments

This work was supported by an Emmy Noether grant from the Deutsche Forschungsgemeinschaft to PB and by EEC grants in the REGIA program to HB and BW. We thank Dr. C. Curie (Montpellier) for irt1-1 seeds.

Supplementary material

425_2007_535_MOESM1_ESM.tif (7.7 mb)
Suppl. Fig. 1 Expression analysis of BHLH038, BHLH039, BHLH100 and BHLH101 in roots in the bhlh ko lines. 10 day-old homozygous insertion plants were transferred for three days to iron deficiency conditions (0 Fe, 50 µM Ferrozine) versus the control (50 µM Fe). Expression was analyzed by quantitative real-time reverse transcription-PCR. Absolute expression levels were normalized against constitutive controls as described in Materials and methods. Note that the T-DNA is inserted in a different orientation in the bhlh101 allele than in the other three bhlh ko alleles. Also not that in all four cases, BHLH primers recognized sites downstream of the T-DNA insertions (TIF 7.65 MB)

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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  • Hong-Yu Wang
    • 1
  • Marco Klatte
    • 1
  • Marc Jakoby
    • 2
  • Helmut Bäumlein
    • 3
  • Bernd Weisshaar
    • 2
    • 4
  • Petra Bauer
    • 1
    Email author
  1. 1.Department of Biosciences, BotanySaarland UniversitySaarbrückenGermany
  2. 2.Max-Planck Institute for Plant Breeding ResearchKölnGermany
  3. 3.Institute of Plant Genetics and Crop Plant Research (IPK)GaterslebenGermany
  4. 4.Faculty of BiologyUniversity of BielefeldBielefeldGermany

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