Identification and characterization of Arabidopsis indole-3-butyric acid response mutants defective in novel peroxisomal enzymes

Genetics. 2008 Sep;180(1):237-51. doi: 10.1534/genetics.108.090399. Epub 2008 Aug 24.


Genetic evidence suggests that indole-3-butyric acid (IBA) is converted to the active auxin indole-3-acetic acid (IAA) by removal of two side-chain methylene units in a process similar to fatty acid beta-oxidation. Previous studies implicate peroxisomes as the site of IBA metabolism, although the enzymes that act in this process are still being identified. Here, we describe two IBA-response mutants, ibr1 and ibr10. Like the previously described ibr3 mutant, which disrupts a putative peroxisomal acyl-CoA oxidase/dehydrogenase, ibr1 and ibr10 display normal IAA responses and defective IBA responses. These defects include reduced root elongation inhibition, decreased lateral root initiation, and reduced IBA-responsive gene expression. However, peroxisomal energy-generating pathways necessary during early seedling development are unaffected in the mutants. Positional cloning of the genes responsible for the mutant defects reveals that IBR1 encodes a member of the short-chain dehydrogenase/reductase family and that IBR10 resembles enoyl-CoA hydratases/isomerases. Both enzymes contain C-terminal peroxisomal-targeting signals, consistent with IBA metabolism occurring in peroxisomes. We present a model in which IBR3, IBR10, and IBR1 may act sequentially in peroxisomal IBA beta-oxidation to IAA.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Acyl-CoA Dehydrogenase / genetics
  • Amino Acid Sequence
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / genetics
  • Gene Expression Regulation, Enzymologic*
  • Gene Expression Regulation, Plant*
  • Genetic Complementation Test
  • Indoles / metabolism*
  • Molecular Sequence Data
  • Mutation*
  • Oxygen / chemistry
  • Peroxisomes / chemistry*
  • Plant Roots / metabolism
  • Protein Structure, Tertiary
  • Sequence Homology, Amino Acid


  • Arabidopsis Proteins
  • Indoles
  • indolebutyric acid
  • Acyl-CoA Dehydrogenase
  • IBR3 protein, Arabidopsis
  • Oxygen