title: Polar localization and degradation of Arabidopsis boron transporters through distinct trafficking pathways.
abstract: Boron (B) is essential for plant growth but is toxic when present in excess. In the roots of Arabidopsis thaliana under B limitation, a boric acid channel, NIP5;1, and a boric acid/borate exporter, BOR1, are required for efficient B uptake and subsequent translocation into the xylem, respectively. However, under high-B conditions, BOR1 activity is repressed through endocytic degradation, presumably to avoid B toxicity. In this study, we investigated the localization of GFP-tagged NIP5;1 and BOR1 expressed under the control of their native promoters. Under B limitation, GFP-NIP5;1 and BOR1-GFP localized preferentially in outer (distal) and inner (proximal) plasma membrane domains, respectively, of various root cells. The polar localization of the boric acid channel and boric acid/borate exporter indicates the radial transport route of B toward the stele. Furthermore, mutational analysis revealed a requirement of tyrosine residues, in a probable cytoplasmic loop region of BOR1, for polar localization in various cells of the meristem and elongation zone. The same tyrosine residues were also required for vacuolar targeting upon high B supply. The present study of BOR1 and NIP5;1 demonstrates the importance of selective endocytic trafficking in polar localization and degradation of plant nutrient transporters for radial transport and homeostasis of plant mineral nutrients.
authors.affiliation: Division of Applied Bioscience, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan. jtakano@abs.agr.hokudai.ac.jp
authors.forename: Junpei
authors.initials: J
authors.lastname: Takano
authors.forename: Mayuki
authors.initials: M
authors.lastname: Tanaka
authors.forename: Atsushi
authors.initials: A
authors.lastname: Toyoda
authors.forename: Kyoko
authors.initials: K
authors.lastname: Miwa
authors.forename: Koji
authors.initials: K
authors.lastname: Kasai
authors.forename: Kentaro
authors.initials: K
authors.lastname: Fuji
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Onouchi
authors.forename: Satoshi
authors.initials: S
authors.lastname: Naito
authors.forename: Toru
authors.initials: T
authors.lastname: Fujiwara
mesh_terms: D017920:Antiporters / Q000378:metabolism*; D020346:Aquaporins / Q000378:metabolism*; D017360:Arabidopsis / Q000166:cytology* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001895:Boron / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D016764:Cell Polarity; D004058:Diffusion; D049452:Green Fluorescent Proteins / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism; D014617:Vacuoles / Q000378:metabolism
chemical_list: D017920:Antiporters; D020346:Aquaporins; D029681:Arabidopsis Proteins; C469216:BOR1 protein, Arabidopsis; C512214:NIP5;1 protein, Arabidopsis; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D014443:Tyrosine; D001895:Boron