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Gene Review

IM  -  alternative oxidase protein IMMUTANS

Arabidopsis thaliana

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High impact information on IM

  • The data presented here are consistent with a role for the IM protein as a cofactor for carotenoid desaturation [1].
  • We show that the IM protein is synthesized as a precursor polypeptide that is imported into chloroplasts and inserted into the thylakoid membrane [1].
  • We propose a model in which IM function is linked to phytoene desaturation and, possibly, to the respiratory activity of the chloroplast [1].
  • We have positionally cloned IM and found that the gene encodes a 40.5-kD protein with sequence motifs characteristic of alternative oxidase, a mitochondrial protein that functions as a terminal oxidase in the respiratory chains of all plants [2].
  • We have cloned the IM gene by transposon tagging and show that even stable null alleles give rise to a variegated phenotype [1].

Biological context of IM


Anatomical context of IM


Associations of IM with chemical compounds

  • The albino sectors of im plants contain reduced levels of carotenoids and increased levels of the carotenoid precursor phytoene [1].
  • The thylakoid membranes of most photosynthetic organisms contain a terminal oxidase (PTOX, the product of the Arabidopsis IMMUTANS gene) that functions in the oxidation of the plastoquinone pool [3].
  • PTOX and AOX are diiron carboxylate proteins, and based on crystal structures of other members of this protein class, a structural model of PTOX has been proposed in which the ligation sphere of the diiron center is composed of six conserved histidine and glutamate residues [3].
  • Overexpression of IM did not result in increased capacity to keep the PQ pool oxidized compared to either the wild type or im grown under control conditions (25 degrees C and photosynthetic photon flux density of 150 mumol photons m(-2) s(-1)) [6].
  • In order to determine whether the newly discovered plastid oxidase (PTOX) involved in carotenoid biosynthesis acts as a plastoquinol oxidase in higher plant chloroplasts, the Arabidopsis thaliana PTOX gene (At-PTOX) was expressed in tobacco under the control of a strong constitutive promoter [7].

Other interactions of IM


Analytical, diagnostic and therapeutic context of IM

  • We tested the functional significance of these residues by site-directed mutagenesis of PTOX in vitro and in planta, taking advantage null immutans alleles for the latter studies [3].
  • In contrast to AOX1a, meta-analyses of published Arabidopsis microarray data indicated that IM expression exhibited minimal modulation in response to myriad abiotic stresses, which is consistent with our functional data [6].
  • Sequence analysis revealed that the amino-acid sequence of OsIM1 showed 66% and 62% identity with PTOX from tomato ( Capsicum annuum) and AtIM from Arabidopsis, both of which encoded chloroplast-orientated terminal oxidase [8].


  1. Mutations in the Arabidopsis gene IMMUTANS cause a variegated phenotype by inactivating a chloroplast terminal oxidase associated with phytoene desaturation. Carol, P., Stevenson, D., Bisanz, C., Breitenbach, J., Sandmann, G., Mache, R., Coupland, G., Kuntz, M. Plant Cell (1999) [Pubmed]
  2. The IMMUTANS variegation locus of Arabidopsis defines a mitochondrial alternative oxidase homolog that functions during early chloroplast biogenesis. Wu, D., Wright, D.A., Wetzel, C., Voytas, D.F., Rodermel, S. Plant Cell (1999) [Pubmed]
  3. Sequences required for the activity of PTOX (IMMUTANS), a plastid terminal oxidase: in vitro and in planta mutagenesis of iron-binding sites and a conserved sequence that corresponds to Exon 8. Fu, A., Park, S., Rodermel, S. J. Biol. Chem. (2005) [Pubmed]
  4. The Arabidopsis immutans mutation affects plastid differentiation and the morphogenesis of white and green sectors in variegated plants. Aluru, M.R., Bae, H., Wu, D., Rodermel, S.R. Plant Physiol. (2001) [Pubmed]
  5. Alterations in photosynthesis in Arabidopsis lacking IMMUTANS, a chloroplast terminal oxidase. Aluru, M.R., Stessman, D.J., Spalding, M.H., Rodermel, S.R. Photosyn. Res. (2007) [Pubmed]
  6. IMMUTANS Does Not Act as a Stress-Induced Safety Valve in the Protection of the Photosynthetic Apparatus of Arabidopsis during Steady-State Photosynthesis. Rosso, D., Ivanov, A.G., Fu, A., Geisler-Lee, J., Hendrickson, L., Geisler, M., Stewart, G., Krol, M., Hurry, V., Rodermel, S.R., Maxwell, D.P., H??ner, N.P. Plant Physiol. (2006) [Pubmed]
  7. Involvement of a plastid terminal oxidase in plastoquinone oxidation as evidenced by expression of the Arabidopsis thaliana enzyme in tobacco. Joët, T., Genty, B., Josse, E.M., Kuntz, M., Cournac, L., Peltier, G. J. Biol. Chem. (2002) [Pubmed]
  8. A new AOX homologous gene OsIM1 from rice (Oryza sativa L.) with an alternative splicing mechanism under salt stress. Kong, J., Gong, J.M., Zhang, Z.G., Zhang, J.S., Chen, S.Y. Theor. Appl. Genet. (2003) [Pubmed]
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