CYP83B1, a cytochrome P450 at the metabolic branch paint in auxin and indole glucosinolate biosynthesis in Arabidopsis

Auxins are growth regulators involved in virtually all aspects of plant dev elopment. However, little is known about how plants synthesize these essent ial compounds. We propose that the level of indole-3-acetic acid is regulat ed by the flux of indole-3-acetaldoxime through a cytochrome P450, CYP83B1, to the glucosinolate pathway. A T-DNA insertion in the CYP83B1 gene leads t o plants with a phenotype that suggests severe auxin overproduction, wherea s CYP83B1 overexpression leads to toss of apical dominance typical of auxin deficit. CYP83B1 N-hydroxylates indole-3-acetaldoxime to the corresponding aci-nitro compound, 1-aci-nitro-2-indolyl-ethane, with a K-m of 3 muM and a turnover number of 53 min(-1). The aci-nitro compound formed reacts non-e nzymatically with thiol compounds to produce an N-alkyl-thiohydroximate add uct, the committed precursor of glucosinolates. Thus, indole-3-acetaldoxime is the metabolic branch point between the primary auxin indole-3-acetic ac id and indole glucosinolate biosynthesis in Arabidopsis.