The main oxidative inactivation pathway of the plant hormone auxin (Nature Comms.)

Auxin is a key hormone in almost all stages of the plant development and its main natural form is  indole-3-acetic acid (IAA). In Arabidopsis, several gene families are involved in auxin homeostasis. In this work, Hayashi et al. focus on the roles of DIOXYGENASE FOR AUXIN OXIDATION 1 (DAO1) which converts IAA to oxIAA; the GH3 gene family encoding for acyl amidotransferases that catalyze the conjugation of IAA with amino acids (forming IAA-Asp and IAA-Glu); and IAA-Leu-Resistant1 (ILR1), a Leu-amidohydrolase which converts IAA-amino acid conjugates to IAA in vitro. Here, the authors describe how IAA is inactivated and recycled through the GH3-ILR1-DAO pathway. Basically, GH3 converts IAA to the storage form IAA-Asp and IAA-Glu, a process that can be reversed by ILR1. If needed, IAA-Asp and IAA-Glu can be oxidized by DAO1 in an irreversible reaction. Then, ILR1 catalyzes the release of the amino acids from oxIAA. This work describes an auxin inactivation pathway that might be important for auxin homeostasis. (Summary by Eva Maria Gomez Alvarez, @eva_ga96) Nature Comms.