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Plant Cell. 2017 Apr;29(4):824-842. doi: 10.1105/tpc.16.00825. Epub 2017 Mar 24.

Polar Localization of the NIP5;1 Boric Acid Channel Is Maintained by Endocytosis and Facilitates Boron Transport in Arabidopsis Roots.

Author information

1
Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai 599-8531, Japan.
2
Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
3
Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
4
Graduate School of Science, Kyoto University, Kyoto 608-8502, Japan.
5
Faculty of Science and Engineering, Konan University, Kobe 658-0072, Japan.
6
Institute of Plant Science and Resources, Okayama University, Kurashiki 710-0046, Japan.
7
Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai 599-8531, Japan jtakano@plant.osakafu-u.ac.jp.

Abstract

Boron uptake in Arabidopsis thaliana is mediated by nodulin 26-like intrinsic protein 5;1 (NIP5;1), a boric acid channel that is located preferentially on the soil side of the plasma membrane in root cells. However, the mechanism underlying this polar localization is poorly understood. Here, we show that the polar localization of NIP5;1 in epidermal and endodermal root cells is mediated by the phosphorylation of Thr residues in the conserved TPG (ThrProGly) repeat in the N-terminal region of NIP5;1. Although substitutions of Ala for three Thr residues in the TPG repeat did not affect lateral diffusion in the plasma membrane, these substitutions inhibited endocytosis and strongly compromised the polar localization of GFP-NIP5;1. Consistent with this, the polar localization was compromised in µ subunit mutants of the clathrin adaptor AP2. The Thr-to-Ala substitutions did not affect the boron transport activity of GFP-NIP5;1 in Xenopus laevis oocytes but did inhibit the ability to complement boron translocation to shoots and rescue growth defects in nip5;1-1 mutant plants under boron-limited conditions. These results demonstrate that the polar localization of NIP5;1 is maintained by clathrin-mediated endocytosis, is dependent on phosphorylation in the TPG repeat, and is necessary for the efficient transport of boron in roots.

PMID:
28341806
PMCID:
PMC5435427
DOI:
10.1105/tpc.16.00825
[Indexed for MEDLINE]
Free PMC Article

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