Structural insights into Arabidopsis thaliana CTS-mediated fatty acid and hormone metabolism

In plants, peroxisomal β oxidation is essential for energy production, sugar metabolism and the regulation of hormonal signaling. The Arabidopsis COMATOSE (CTS) gene, which encodes the peroxisomal ATP-binding cassette transporter ABCD1 (also known as CTS or PAX1), mediates the import of various fatty acyls and hormones into peroxisomes for β oxidation. Although physiological evidence has demonstrated that defects in CTS impair plant development and growth, the underlying molecular mechanisms remain poorly understood. In this study, biochemical assays confirm that CTS transports a broad range of fatty acyl-CoAs, as well as indole-3-butyric acid (IBA), an auxin and precursor to indole-3-aceditc acid, and auxin herbicide 2,4-dichlorophenoxy butyric acid (2,4-DB). We further solve five cryo-EM structures of CTS: the apo form, ATP-bound, and three substrate-bound states (C12:0-, IBA- and 2,4-DB-CoA) at near-atom resolutions. These structures reveal that CTS binds a single substrate molecule in a characteristic U-shaped conformation. Moreover, physiological studies using point mutations of key substrate-binding residues identify critical residues essential for its function. Our findings reveal the molecular principles by which CTS integrates lipid metabolism, hormone regulation, and xenobiotic activation throughout the plant life cycle, as well as underscore its potential as a target for crop improvement and herbicide development.