Cis-cinnamic acid is a novel natural auxin efflux inhibitor that promotes lateral root formation Journal Article

Author(s): Steenackers, Ward; Klíma, Petr; Quareshy, Mussa Q; Cesarino, Igor; Kumpf, Robert P; Corneillie, Sander; Araújo, Pedro; Viaene, Tom; Goeminne, Geert; Nowack, Moritz K; Ljung, Karin; Friml, Jiří; Blakeslee, Joshua J; Novák, Ondřej; Zažímalová, Eva; Napier, Richard; Boerjan, Wout; Vanholme, Bartel
Article Title: Cis-cinnamic acid is a novel natural auxin efflux inhibitor that promotes lateral root formation
Affiliation IST Austria
Abstract: Auxin steers numerous physiological processes in plants, making the tight control of its endogenous levels and spatiotemporal distribution a necessity. This regulation is achieved by different mechanisms, including auxin biosynthesis, metabolic conversions, degradation, and transport. Here, we introduce cis-cinnamic acid (c-CA) as a novel and unique addition to a small group of endogenous molecules affecting in planta auxin concentrations. c-CA is the photo-isomerization product of the phenylpropanoid pathway intermediate trans-CA (t-CA). When grown on c-CA-containing medium, an evolutionary diverse set of plant species were shown to exhibit phenotypes characteristic for high auxin levels, including inhibition of primary root growth, induction of root hairs, and promotion of adventitious and lateral rooting. By molecular docking and receptor binding assays, we showed that c-CA itself is neither an auxin nor an anti-auxin, and auxin profiling data revealed that c-CA does not significantly interfere with auxin biosynthesis. Single cell-based auxin accumulation assays showed that c-CA, and not t-CA, is a potent inhibitor of auxin efflux. Auxin signaling reporters detected changes in spatiotemporal distribution of the auxin response along the root of c-CA-treated plants, and long-distance auxin transport assays showed no inhibition of rootward auxin transport. Overall, these results suggest that the phenotypes of c-CA-treated plants are the consequence of a local change in auxin accumulation, induced by the inhibition of auxin efflux. This work reveals a novel mechanism how plants may regulate auxin levels and adds a novel, naturally occurring molecule to the chemical toolbox for the studies of auxin homeostasis.
Journal Title: Plant Physiology
Volume: 173
Issue 1
ISSN: 1532-2548
Publisher: American Society of Plant Biologists  
Date Published: 2017-01-01
Start Page: 552
End Page: 565
Copyright Statement: Copyright © 2017 American Society of Plant Biologists. All rights reserved.
DOI: 10.1104/pp.16.00943
Notes: We thank Ottoline Leyser (Sainsbury Laboratory, University of Cambridge) for providing us p35S:iaaL Arabidopsis seeds. We thank Karel Spruyt for imaging wherever needed, Toon Babylon for technical assistance, Wei Xua and Davy Opdenacker for help with the pDR5:LUC experiments, and Tao Fang and Hans Motte for providing us with the Selaginella moellendorffii plantlets. We also appreciated the help of the VIB Imaging Core facility, namely Amanda Gonçalves, who helped with analyzing the imaging experiments, and Dominic Petrella for critical reading of the manuscript. Finally, we thank Wim Grunewald, Tom Beeckman, Steffen Vanneste, Bert De Rybel, and Jürgen Kleine-Vehn for scientific discussions.
Open access: yes (OA journal)