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Gene Review

FRO4  -  ferric reduction oxidase 4

Arabidopsis thaliana

Synonyms: ATFRO4, MZF18.14, MZF18_14
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High impact information on ATFRO4/FRO4

  • FRO2 belongs to a superfamily of flavocytochromes that transport electrons across membranes [1].
  • There is a nonsense mutation within the first exon of FRO2 in frd1-1 and a missense mutation within FRO2 in frd1-3 [1].
  • Introduction of functional FRO2 complements the frd1-1 phenotype in transgenic plants [1].
  • We propose a new model for iron uptake in Arabidopsis where FRO2 and IRT1 are differentially regulated by FIT1 [2].
  • Additionally, frd4 chloroplasts are smaller in size and possess dramatically fewer thylakoid membranes and grana stacks when compared with wild-type chloroplasts. frd4 mutant plants express both FRO2 and IRT1 mRNA normally in their roots under iron deficiency, arguing against any defects in systemic iron-deficiency signaling [3].

Biological context of ATFRO4/FRO4

  • Considering the tissue-specific expression profiles of AtFRO genes, we suggest that AtFRO2 and AtFRO3 are two Fe(III) chelate reductases mainly functioning in iron acquisition and metabolism in Arabidopsis roots, while AtFRO5, AtFRO6, AtFRO7 and AtFRO8 are required for iron homeostasis in different tissues of shoots [4].
  • Regulation of the root high-affinity iron uptake system by whole-plant signals was investigated at the molecular level in Arabidopsis, through monitoring FRO2 and IRT1 gene expression [5].

Anatomical context of ATFRO4/FRO4

  • The Arabidopsis FRO2 gene encodes the iron deficiency-inducible ferric chelate reductase responsible for reduction of iron at the root surface; subsequent transport of iron across the plasma membrane is carried out by a ferrous iron transporter (IRT1) [6].
  • To account for the results presented, we propose that AtNRAMP3 influences metal accumulation and IRT1 and FRO2 gene expression by mobilizing vacuolar metal pools to the cytosol [7].

Associations of ATFRO4/FRO4 with chemical compounds

  • This paper is a study of the effects of ethylene inhibitors and precursors on the expression of the genes encoding the ferric reductases and iron transporters of Arabidopsis thaliana (FRO2 and IRT1) and Lycopersicon esculentum (=Solanum lycopersicum) (FRO1 and IRT1) plants [8].
  • The large water soluble domain of FRO2, which contains NADPH, FAD and oxidoreductase sequence motifs, was located on the inside of the membrane [9].
  • Steady-state mRNA levels of FRO2 and IRT1 are also coordinately regulated by zinc and cadmium [10].

Other interactions of ATFRO4/FRO4

  • AtFRO2 and AtFRO3 were mainly expressed in roots of Arabidopsis, AtFRO5 and AtFRO6 in shoots and flowers, and AtFRO7 in cotyledons and trichomes, whereas the transcription of AtFRO8 was specific for leaf veins [4].


  1. A ferric-chelate reductase for iron uptake from soils. Robinson, N.J., Procter, C.M., Connolly, E.L., Guerinot, M.L. Nature (1999) [Pubmed]
  2. The essential basic helix-loop-helix protein FIT1 is required for the iron deficiency response. Colangelo, E.P., Guerinot, M.L. Plant Cell (2004) [Pubmed]
  3. Arabidopsis cpFtsY mutants exhibit pleiotropic defects including an inability to increase iron deficiency-inducible root Fe(III) chelate reductase activity. Durrett, T.P., Connolly, E.L., Rogers, E.E. Plant J. (2006) [Pubmed]
  4. Molecular and biochemical characterization of the Fe(III) chelate reductase gene family in Arabidopsis thaliana. Wu, H., Li, L., Du, J., Yuan, Y., Cheng, X., Ling, H.Q. Plant Cell Physiol. (2005) [Pubmed]
  5. Dual regulation of the Arabidopsis high-affinity root iron uptake system by local and long-distance signals. Vert, G.A., Briat, J.F., Curie, C. Plant Physiol. (2003) [Pubmed]
  6. Expression profiling of the Arabidopsis ferric chelate reductase (FRO) gene family reveals differential regulation by iron and copper. Mukherjee, I., Campbell, N.H., Ash, J.S., Connolly, E.L. Planta (2006) [Pubmed]
  7. AtNRAMP3, a multispecific vacuolar metal transporter involved in plant responses to iron deficiency. Thomine, S., Lelièvre, F., Debarbieux, E., Schroeder, J.I., Barbier-Brygoo, H. Plant J. (2003) [Pubmed]
  8. Ethylene could influence ferric reductase, iron transporter, and H+-ATPase gene expression by affecting FER (or FER-like) gene activity. Lucena, C., Waters, B.M., Romera, F.J., Garc??a, M.J., Morales, M., Alc??ntara, E., P??rez-Vicente, R. J. Exp. Bot. (2006) [Pubmed]
  9. Transmembrane topology of FRO2, a ferric chelate reductase from Arabidopsis thaliana. Schagerlöf, U., Wilson, G., Hebert, H., Al-Karadaghi, S., Hägerhäll, C. Plant Mol. Biol. (2006) [Pubmed]
  10. Overexpression of the FRO2 ferric chelate reductase confers tolerance to growth on low iron and uncovers posttranscriptional control. Connolly, E.L., Campbell, N.H., Grotz, N., Prichard, C.L., Guerinot, M.L. Plant Physiol. (2003) [Pubmed]
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