Metabolism meets transport: a new perspective on auxin homeostasis at subcellular level.

This review highlights recent advances revealing auxin homeostasis as an integrated network of metabolism and transport, emphasizing subcellular compartmentalization as a key regulatory principle. Indole-3-acetic acid (IAA), the principal auxin, is a central regulator of plant growth and development throughout the plant life cycle. Recent discoveries have reshaped our understanding of auxin metabolism and highlighted its close integration with auxin transport in maintaining cellular homeostasis. This review summarizes current knowledge on IAA metabolism and places it into the broader framework of auxin distribution within plant cells. The spatial distribution of auxin is tightly linked to its metabolic regulation, as localized auxin accumulation underlies many developmental and signaling processes. Subcellular compartmentalization of auxin into organelles such as the endoplasmic reticulum or vacuole is closely associated with metabolic modifications that influence auxin transport and availability, although the mechanisms governing the movement of auxin conjugates across organellar membranes remain poorly understood. Directed auxin transport delivers active IAA to specific intracellular sites where enzymes catalyze its conjugation, hydrolysis, or degradation. Together, these interconnected processes create a dynamic regulatory network that coordinates auxin metabolism, transport, and compartmentalization to maintain auxin homeostasis and ensure precise control of plant growth and development.