Involved in valine catabolism. May be indirectly involved in benzoic acid biosynthesis and in cold signaling and cold tolerance. 3-hydroxy-2-methylpropanoyl-CoA + H2O = 3-hydroxy-2-methylpropanoate + CoA + H(+) Inhibited by copper. Can also use 3-hydroxy-3-phenoylpropionoyl-CoA and p-coumaroyl-CoA as substrates, but not benzoyl-CoA. Optimum pH is 7-9. Amino-acid degradation; L-valine degradation. Expressed in roots, leaves, flowers and siliques. Induced during post-germinative growth. Detected in imbibed seeds. Down-regulated by sugar. Resistant to inhibition of root elongation and promotion of lateral root formation by the auxin precursor indole-3-butyric acid (IBA). Deficiency of benzoic acid-containing glucosinolates in the seeds. Resistance to the pro-herbicide 2,4-dichlorophenoxybutyric acid (2,4-DB). Loss of function mutants are defective in beta-oxidization of fatty acids and in the conversion of indole-3-butyric acid (IBA) to indole-3-acetic acid (IAA). These inhibitions may be due to the accumulation of a toxic intermediate. The mutants are also less tolerant to freezing stress after cold acclimation. Belongs to the enoyl-CoA hydratase/isomerase family.