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New Phytol. 2016 Oct;212(2):497-509. doi: 10.1111/nph.14049. Epub 2016 Jun 20.

Cytokinins influence root gravitropism via differential regulation of auxin transporter expression and localization in Arabidopsis.

Author information

1
CEITEC - Central European Institute of Technology, Masaryk University, Brno, CZ-62500, Czech Republic.
2
Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Brno, CZ-62500, Czech Republic.
3
Institute of Science and Technology (IST), Klosterneuburg, AT-3400, Austria.
4
Institute of Biostatistics and Analyses, Faculty of Medicine and Faculty of Science, Masaryk University, Brno, CZ-62500, Czech Republic.
5
Department of Chemical Biology and Genetics, Centre of the Region Hana for Biotechnological and Agricultural Research, Faculty of Science, Palacky University, Olomouc, CZ-78371, Czech Republic.
6
CEITEC - Central European Institute of Technology, Masaryk University, Brno, CZ-62500, Czech Republic. hejatko@sci.muni.cz.
7
Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Brno, CZ-62500, Czech Republic. hejatko@sci.muni.cz.

Abstract

Redirection of intercellular auxin fluxes via relocalization of the PIN-FORMED 3 (PIN3) and PIN7 auxin efflux carriers has been suggested to be necessary for the root gravitropic response. Cytokinins have also been proposed to play a role in controlling root gravitropism, but conclusive evidence is lacking. We present a detailed study of the dynamics of root bending early after gravistimulation, which revealed a delayed gravitropic response in transgenic lines with depleted endogenous cytokinins (Pro35S:AtCKX) and cytokinin signaling mutants. Pro35S:AtCKX lines, as well as a cytokinin receptor mutant ahk3, showed aberrations in the auxin response distribution in columella cells consistent with defects in the auxin transport machinery. Using in vivo real-time imaging of PIN3-GFP and PIN7-GFP in AtCKX3 overexpression and ahk3 backgrounds, we observed wild-type-like relocalization of PIN proteins in the columella early after gravistimulation, with gravity-induced relocalization of PIN7 faster than that of PIN3. Nonetheless, the cellular distribution of PIN3 and PIN7 and expression of PIN7 and the auxin influx carrier AUX1 was affected in AtCKX overexpression lines. Based on the retained cytokinin sensitivity in pin3 pin4 pin7 mutant, we propose the AUX1-mediated auxin transport rather than columella-located PIN proteins as a target of endogenous cytokinins in the control of root gravitropism.

KEYWORDS:

AUX1; Arabidopsis; PIN-FORMED (PIN); auxin; cytokinins; root gravitropism

PMID:
27322763
DOI:
10.1111/nph.14049
[Indexed for MEDLINE]
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