From oxime to signal molecules: Indole-3-acetaldoxime undergoes oxidation to produce nitric oxide and indole-3-acetic acid.

Indole-3-acetaldoxime (IAOx) has long been placed in auxin metabolism as a tryptophan-derived precursor that may feed indole-3-acetic acid (IAA) production through indole-3-acetonitrile (IAN) and indole-3-acetamide (IAM). However, recent genetic and biochemical evidence indicates that IAOx-derived IAA formation is not adequately explained by a single obligate linear pathway. Here, we discuss an emerging model in which IAOx acts as a redox-sensitive metabolic branch point. In this model, IAOx can partition into multiple pathways. The peroxidase-dependent oxidative pathway produces nitric oxide (NO) together with indole-3-acetaldehyde (IAAld). Because IAAld can be further oxidized toward IAA, this reaction provides a potential biochemical link between NO production and IAA biosynthesis. We also highlight the upstream role of CYP79 enzymes in defining the spatial and taxonomic distribution of oxime pools, and we compare this modular plant strategy with animal nitric oxide synthase-dependent NO formation. This framework refines the relationship between IAOx metabolism, redox control, NO production, and auxin-dependent development and stress responses.