During her PhD, Inès focused on two auxin transporters in plants: WAT1 and PIN8. Plant growth, development, and environmental adaptation rely on several hormone classes, among which auxin is one of the most extensively studied. Despite its central role, the transport mechanisms of auxin remain incompletely understood. Inès investigated auxin transport at the subcellular level, particularly how WAT1 mediates its movement within plant cells via a proton-coupled symport mechanism. She uncovered the transporter’s substrate specificity, which notably includes synthetic auxins widely used in agriculture. Through in vivo experiments in Arabidopsis thaliana, she revealed a previously undescribed mutant phenotype, shedding new light on WAT1’s physiological function. In parallel, she structurally characterised the auxin transporter PIN8 in complex with the herbicide Morphactin (Cl-HFC), providing the first mechanistic insight into how this compound inhibits PIN transporters. She discovered that Cl-HFC locks PIN8 in an outward-facing conformation, thereby preventing auxin translocation. Biophysical assays confirmed that Cl-HFC is more potent than commonly used PIN inhibitors such as NPA. The structural analysis uncovered a chlorine-dependent interaction network that underpins Cl-HFC’s high binding affinity and specificity. Unlike phenoxyacetic acid-based herbicides, this inhibition mechanism is unique to PIN transporters. These findings lay the groundwork for the development of next-generation, PIN-specific herbicides with improved selectivity and efficacy in agricultural applications.

The PhD study was completed at the Department of Molecular Biology and Genetics, Faculty of Natural Sciences, Aarhus University.

This summary was prepared by the PhD student.

Time: Wednesday, 2 July 2025 at 13:00
Place: Building 1871, room 120, Lecture Theatre AUD Nucleus, Department of Molecular Biology and Genetics, Aarhus University Universitetsbyen 81, 8000 Aarhus
Title of PhD thesis: Hormones on the move: The quiet mood swings inside plants
Contact information: Inès Benhammouche, e-mail: ines.benhammouche@mbg.au.dk, tel.: +45 23118480
Members of the assessment committee:
Associate Professor Henriette Elisabeth Autzen, Department of Biomedical Sciences, Molecular and Translational Pharmacology, University of Copenhagen, Denmark
Professor Dr. Ekkehard Neuhaus, Department of Plant Physiology, University of Kaiserslautern-Landau, Germany
Associate Professor Lotte Bjergbæk (chair), Department of Molecular Biology and Genetics, Aarhus University, Denmark
Main supervisor: Professor Bjørn Panyella Pedersen, Department of Molecular Biology and Genetics, Aarhus University, Denmark
Language: The PhD dissertation will be defended in English

The defence is public.
The PhD thesis is available for reading at the Graduate School of Natural Sciences/GSNS, Ny Munkegade 120, building 1521, 8000 Aarhus C.