Redox-regulated Aux/IAA multimerization modulates auxin responses

Reactive oxygen species (ROS) function as key signals in plant adaptation to environmental stresses, such as drought. Roots respond to transient water unavailability by temporarily ceasing branching through the acclimative response xerobranching. In this study, we report how a xerobranching stimulus triggers rapid changes of ROS levels in root nuclei, triggering redox-dependent multimerization of the auxin repressor protein IAA3. Mutations in specific cysteine residues of IAA3 disrupt redox-mediated multimerization and interaction with co-repressor TPL, thereby attenuating IAA3-mediated target gene repression. Other AUX/IAA proteins also vary in their redox-mediated multimerization, which reveals a regulatory mechanism that connects dynamic changes in cellular redox status to auxin signaling. Our study reveals how ROS, auxin, and water availability intersect and shape root adaptive responses, thereby maintaining phenotypic plasticity in plants.