Aldoximes: compounds at the crossroads of multiple metabolic pathways in plant

Aldoximes are amino acid-derivatives well recognized as precursors of defense compounds, such as glucosinolates and cyanogenic glycosides. However, recent studies have elucidated the multifaceted roles of aldoximes in plant survival beyond defense, as they exert influence over multiple metabolic pathways, including auxin biosynthesis and the phenylpropanoid pathway. Aldoxime accumulation affects the homeostasis of auxin, an essential plant hormone that controls almost every aspect of plant growth and development. While auxin biosynthesis primarily occurs through the conserved TAA/YUC pathway, tryptophan-derived aldoxime and phenylalanine-derived aldoxime also serve as precursors of two major auxins, indole-3-acetic acid (IAA) and phenylacetic acid (PAA), respectively. Notably, this conversion process is not limited to Brassicales and is present in monocots like maize and sorghum. Furthermore, in Brassicales, the accumulation of aldoximes derived from aliphatic and aromatic amino acids represses the phenylpropanoid pathway that produces an array of specialized metabolites crucial for plant survival. These novel findings extend beyond the conventional understanding of aldoximes and shed light on their intricate involvement in enhancing plant fitness. In this review, we discuss the role of aldoximes as precursors for auxins and their inhibitory effect on phenylpropanoid biosynthesis. We also explore the mechanisms by which aldoximes influence these metabolic pathways. Finally, we discuss the implications of these findings for our understanding of plant biology.