Latest Publications
Richard Napier publications
PIN structures shed light on their mechanism of auxin efflux
Chitra Joshi and Richard Napier
Polar auxin transport is a quintessential feature of higher plant physiology and it has been known for many years that some of the primary drivers of polar auxin transport are the PIN-formed (PIN) auxin efflux proteins. Formative research established many key biochemical features of the transport system and discovered inhibitors such as 1-naphtylphthalamic acid (NPA), but the mechanism of action of PINs has remained elusive. This changed in 2022 with the publication of high-resolution structures of the membrane-spanning domains of three PIN proteins. The atomic structures and associated activity assays reveal that PINs use an elevator mechanism to transport auxin anions out of the cell. NPA was shown to be a competitive inhibitor that traps PINs in their inward-open conformation. The secrets of the hydrophilic cytoplasmic loop of PIN proteins remain to be discovered.
Journal of Experimental Botany. May 2023
Non-specific effects of the CINNAMATE-4-HYDROXYLASE inhibitor piperonylic acid
Ilias El Houaria, Petr Klíma, Alexandra Baekelandt, Paul E. Staswick, Veselina Uzunova, Charo I. Del Genio, Ward Steenackers, Petre I. Dobrev, Roberta Filepová, Ondrej Novák, Richard Napier, Jan Petrášek, Dirk Inzé, Wout Boerjan, Bartel Vanholme
Chemical inhibitors are often implemented for the functional characterization of genes to overcome the limitations associated with genetic approaches. Here we illustrate the cause and implications of such secondary effects by focusing on piperonylic acid (PA), an inhibitor of CINNAMATE-4-HYDROXYLASE (C4H) that is frequently used to investigate the involvement of lignin during plant growth and development. When supplied to plants, we found that PA is recognized as a substrate by GRETCHEN HAGEN 3.6 (GH3.6), an amido synthetase involved in the formation of the indole-3-acetic acid (IAA) conjugate IAA-Asp. We conclude that deregulation of phytohormone homeostasis by surrogate occupation of the conjugation machinery in the plant is likely a general phenomenon when using chemical inhibitors. Our results hereby provide a novel and important basis for future reference in studies using chemical inhibitors. The Plant Journal. April 2023