Involved with IBR3 and IBR10 in the peroxisomal beta-oxidation of indole-3-butyric acid (IBA) to form indole-3-acetic acid (IAA), a biologically active auxin. May be responsible for catalyzing the dehydrogenation step in the conversion of IBA (PubMed:20562230). May be involved in the peroxisomal activation of 2,4-dichlorophenoxybutyric acid (2,4-DB), a precursor of active auxins that inhibit root growth (PubMed:19043666). Defective in root hair expansion (PubMed:20562230). Mutant plants are resistant to the inhibitory effect of intermediate levels of indole-3-butyric acid (IBA) and 2,4-DB on root elongation (PubMed:18725356, PubMed:19043666). Belongs to the short-chain dehydrogenases/reductases (SDR) family.