WOX5-IAA17 feedback circuit mediated cellular auxin response is crucial for Arabidopsis root patterning
Krzysztof Wabnik,^{1, §} Huiyu Tian,^{2, §}Hanbing Li,³ Stephan Pollmann,⁵ Steffen Vanneste,¹ Willy Govaerts,⁶ Jakub Rolčík⁴, Markus Geisler,⁷ Jiří Friml¹ and Zhaojun Ding,^1,2*

¹Department of Plant Systems Biology, VIB and Department of Plant Biotechnology and Genetics, Ghent University, B-9052 Gent, Belgium.
²The Key Laboratory of Plant Cell Engineering and Germplasm Innovation, Ministry of Education, School of Life Sciences, Shandong University, Shanda Nanlu 27, Jinan 250100, China.
³Department of Biochemistry, University of Missouri, Columbia, MO, USA.
⁴Laboratory of Growth Regulators, Centre of the Region Haná for Biotechnological and Agricultural Research and Faculty of Science, Palacký University, 78371 Olomouc, Czech Republic.
⁵Ruhr-Universität Bochum, Lehrstuhl für Pflanzenphysiologie, 44801 Bochum Germany.
⁶Department of Applied Mathematics and Computer Science, Ghent University, 9000 Gent, Belgium.
⁷Department of Biology, Plant Biology, University of Fribourg, 1700 Fribourg, Switzerland.
§These authors contributed equally to this work.
*Corresponding Author：Tel: (+86531) 88362351; E-mail:dingzhaojun@sdu.edu.cn

Abstract
In plants, the patterning of root meristem requires a gradient-guided auxin maximum that depends on the concerted action of polar auxin transport, auxin biosnythesis and intracellular auxin homeostasis. However, mechanisms underlying this auxin gradient dependent root patterning are not fully understood. Here, we present unexpected evidence that the activity of WUSCHEL-RELATED HOMEOBOX 5 (WOX5) transcription factor modulates free auxin production in the quiescent center (QC) of the root and thus assures the maintenance of auxin maximum in the root tip. Moreover, WOX5 expression is inhibited in a feedback-dependent manner by canonical auxin signaling that involves indole-3-acetic acid 17(IAA17) auxin response repressor. Finally, we used loss-of-function and gain-of-function mutant analysis complemented by computer simulation study to identify and test the novel feedback mechanism that links WOX5-dependent auxin production to IAA17-mediated cellular auxin responses. Our findings demonstrate that this feedback circuit is essential for the maintenance of auxin gradient in the root tip and the auxin-mediated root distal stem cell (DSC) differentiation.    

Key words: WOX5, auxin, IAA17/AXR3, root patterning, computer simulation.