title: Termination of Shoot Gravitropic Responses by Auxin Feedback on PIN3 Polarity.
abstract: Plants adjust their growth according to gravity. Gravitropism involves gravity perception, signal transduction, and asymmetric growth response, with organ bending as a consequence [1]. Asymmetric growth results from the asymmetric distribution of the plant-specific signaling molecule auxin [2] that is generated by lateral transport, mediated in the hypocotyl predominantly by the auxin transporter PIN-FORMED3 (PIN3) [3-5]. Gravity stimulation polarizes PIN3 to the bottom sides of endodermal cells, correlating with increased auxin accumulation in adjacent tissues at the lower side of the stimulated organ, where auxin induces cell elongation and, hence, organ bending. A curvature response allows the hypocotyl to resume straight growth at a defined angle [6], implying that at some point auxin symmetry is restored to prevent overbending. Here, we present initial insights into cellular and molecular mechanisms that lead to the termination of the tropic response. We identified an auxin feedback on PIN3 polarization as underlying mechanism that restores symmetry of the PIN3-dependent auxin flow. Thus, two mechanistically distinct PIN3 polarization events redirect auxin fluxes at different time points of the gravity response: first, gravity-mediated redirection of PIN3-mediated auxin flow toward the lower hypocotyl side, where auxin gradually accumulates and promotes growth, and later PIN3 polarization to the opposite cell side, depleting this auxin maximum to end the bending. Accordingly, genetic or pharmacological interference with the late PIN3 polarization prevents termination of the response and leads to hypocotyl overbending. This observation reveals a role of auxin feedback on PIN polarity in the termination of the tropic response.
authors: Institute of Science and Technology (IST) Austria, 3400 Klosterneuburg, Austria; Department of Plant Systems Biology, VIB and Department of Plant Biotechnology and Bioinformatics, Ghent University, 9052 Gent, Belgium.
authors: Hana
authors: H
authors: Rakusová
authors: Institute of Science and Technology (IST) Austria, 3400 Klosterneuburg, Austria.
authors: Mohamad
authors: M
authors: Abbas
authors: Institute of Science and Technology (IST) Austria, 3400 Klosterneuburg, Austria.
authors: Huibin
authors: H
authors: Han
authors: Institute of Science and Technology (IST) Austria, 3400 Klosterneuburg, Austria; Key Laboratory of Protected Horticulture of Liaoning Province, Shenyang Agriculture University, Shenyang 110161, P.R.C.
authors: Siyuan
authors: S
authors: Song
authors: Mendel Centre for Genomics and Proteomics of Plants Systems, CEITEC MU - Central European Institute of Technology, Masaryk University, 625 00 Brno, Czech Republic.
authors: Hélène S
authors: HS
authors: Robert
authors: Institute of Science and Technology (IST) Austria, 3400 Klosterneuburg, Austria. Electronic address: jiri.friml@ist.ac.at.
authors: Jiří
authors: J
authors: Friml
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D025461:Feedback, Physiological; D018522:Gravitropism; D018466:Gravity Sensing; D007210:Indoleacetic Acids / Q000378:metabolism*; D010937:Plant Growth Regulators / Q000378:metabolism*; D018520:Plant Shoots / Q000254:growth & development
chemical_list: D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; C449300:PIN3 protein, Arabidopsis; D010937:Plant Growth Regulators
keywords: Arabidopsis; PIN polarity; auxin; auxin feedback; auxin transport; gravitropism; hypocotyl