Polar Localization of the NIP5;1 Boric Acid Channel Is Maintained by Endocytosis and Facilitates Boron Transport in Arabidopsis Roots.
Boron uptake inArabidopsis thalianais 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 inXenopus laevisoocytes but did inhibit the ability to complement boron translocation to shoots and rescue growth defects innip5;1-1mutant 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.
Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai 599-8531, Japan.|Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.|Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
Sheliang
http://orcid.org/0000-0003-2237-8189
S
Wang
Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai 599-8531, Japan.|Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
Akira
A
Yoshinari
Graduate School of Science, Kyoto University, Kyoto 608-8502, Japan.
Tomoo
T
Shimada
Graduate School of Science, Kyoto University, Kyoto 608-8502, Japan.|Faculty of Science and Engineering, Konan University, Kobe 658-0072, Japan.
Ikuko
http://orcid.org/0000-0001-8814-1593
I
Hara-Nishimura
Institute of Plant Science and Resources, Okayama University, Kurashiki 710-0046, Japan.
Namiki
N
Mitani-Ueno
Institute of Plant Science and Resources, Okayama University, Kurashiki 710-0046, Japan.
Jian
http://orcid.org/0000-0003-3411-827X
J
Feng Ma
Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
Satoshi
http://orcid.org/0000-0001-7006-5609
S
Naito
Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai 599-8531, Japan jtakano@plant.osakafu-u.ac.jp.|Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
Junpei
http://orcid.org/0000-0002-7474-3101
J
Takano
D020346:Aquaporins / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000235:genetics / Q000502:physiology; D001895:Boron / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004705:Endocytosis / Q000235:genetics / Q000502:physiology*; D018517:Plant Roots / Q000378:metabolism*
D020346:Aquaporins; D029681:Arabidopsis Proteins; C512214:NIP5;1 protein, Arabidopsis; D001895:Boron