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Cytokinins influence root gravitropism via differential regulation of auxin transporter expression and localization in Arabidopsis
Author(s) -
Pernisova Marketa,
Prat Tomas,
Grones Peter,
Harustiakova Danka,
Matonohova Martina,
Spichal Lukas,
Nodzynski Tomasz,
Friml Jiri,
Hejatko Jan
Publication year - 2016
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.14049
Subject(s) - gravitropism , auxin , microbiology and biotechnology , cytokinin , biology , mutant , columella , arabidopsis , root cap , green fluorescent protein , arabidopsis thaliana , lateral root , polar auxin transport , biophysics , botany , biochemistry , meristem , anatomy , gene , shoot , nose
Summary Redirection of intercellular auxin fluxes via relocalization of the PIN ‐ FORMED 3 ( PIN 3) and PIN 7 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:At CKX ) and cytokinin signaling mutants. Pro35S:At CKX 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 PIN 3‐ GFP and PIN 7‐ GFP in At CKX 3 overexpression and ahk3 backgrounds, we observed wild‐type‐like relocalization of PIN proteins in the columella early after gravistimulation, with gravity‐induced relocalization of PIN 7 faster than that of PIN 3. Nonetheless, the cellular distribution of PIN 3 and PIN 7 and expression of PIN 7 and the auxin influx carrier AUX 1 was affected in At CKX overexpression lines. Based on the retained cytokinin sensitivity in pin3 pin4 pin7 mutant, we propose the AUX 1‐mediated auxin transport rather than columella‐located PIN proteins as a target of endogenous cytokinins in the control of root gravitropism.