In recent years, substantial progress has been made in exploring auxin conjugation and metabolism, primarily aiming at indole-3-acetic acid (IAA). However, the metabolic regulation of another key auxin, phenylacetic acid (PAA), remains largely uncharacterized. Here, we provide a comprehensive exploration of PAA metabolism in land plants. Through LC-MS screening across multiple plant species and their organs, we identified four previously unreported endogenous PAA metabolites: phenylacetyl-leucine, phenylacetyl-phenylalanine, phenylacetyl-valine, and phenylacetyl-glucose. Enzyme assays, genetic evidence, crystal structures, and docking studies demonstrate that PAA and IAA share core metabolic machinery, revealing a complex regulatory network that maintains auxin homeostasis. Furthermore, our study of PAA conjugation with amino acids and glucose suggests limited compensatory mechanisms within known conjugation pathways, pointing to the existence of alternative metabolic routes in land plants. These insights advance our knowledge of auxin-specific metabolic networks and highlight the unique complexity within plant hormone regulation.

• Keywords
• Auxin, Gretchen Hagen 3, HPLC-MS/MS, conjugation, glucosyl ester, indole-3-acetic acid, metabolism, phenylacetic acid, plant,
• MeSH
• Phenylacetates * metabolism   MeSH
• Indoleacetic Acids metabolism   MeSH
• Metabolic Networks and Pathways * MeSH
• Plant Growth Regulators * metabolism   MeSH
• Embryophyta * metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Phenylacetates * MeSH
• Indoleacetic Acids MeSH
• phenylacetic acid MeSH Browser
• Plant Growth Regulators * MeSH

Auxin glycosylation plays a fundamental role in the regulation of auxin homeostasis, activity, and transport, contributing to the dynamic control of plant growth and development. Glycosylation enhances auxin stability, solubility, and storage capacity, serving as a key mechanism for both temporary inactivation and long-term storage of auxin molecules. Specific glycosyltransferases are critical for this process, catalyzing glycosylation at either the carboxyl group or the nitrogen atom of the indole ring. The storage roles of glycosylated auxins, such as IAA-N-Glc, have been shown to be essential during embryogenesis and seed germination, while irreversible conjugation into catabolic products helps to maintain auxin homeostasis in vegetative tissues. This review highlights the diversity, enzymatic specificity, and physiological relevance of auxin glycosylation pathways, including a frequently overlooked N-glycosylation, underscoring its importance in the complex network of auxin metabolism.

• MeSH
• Glycosylation MeSH
• Homeostasis * MeSH
• Indoleacetic Acids * metabolism   MeSH
• Plant Growth Regulators metabolism   MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Indoleacetic Acids * MeSH
• Plant Growth Regulators MeSH