Identification and characterization of Arabidopsis indole-3-butyric acid response mutants defective in novel peroxisomal enzymes.
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.
Zolman
Bethany K
BK
Department of Biology, University of Missouri, St. Louis, Missouri 63121, USA. zolmanb@umsl.edu
Martinez
Naxhiely
N
Millius
Arthur
A
Adham
A Raquel
AR
Bartel
Bonnie
B
D042964:Acyl-CoA Dehydrogenase / Q000235:genetics; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D007211:Indoles / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D010100:Oxygen / Q000737:chemistry; D020675:Peroxisomes / Q000737:chemistry*; D018517:Plant Roots / Q000378:metabolism; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
D029681:Arabidopsis Proteins; D007211:Indoles; C014612:indolebutyric acid; D042964:Acyl-CoA Dehydrogenase; C520627:IBR3 protein, Arabidopsis; D010100:Oxygen