title: Arabidopsis boron transporter for xylem loading.
abstract: Boron deficiency hampers the productivity of 132 crops in more than 80 countries. Boron is essential in higher plants primarily for maintaining the integrity of cell walls and is also beneficial and might be essential in animals and in yeast. Understanding the molecular mechanism(s) of boron transport is crucial for alleviating boron deficiency. Here we describe the molecular identification of boron transporters in biological systems. The Arabidopsis thaliana mutant bor1-1 is sensitive to boron deficiency. Uptake studies indicated that xylem loading is the key step for boron accumulation in shoots with a low external boron supply and that the bor1-1 mutant is defective in this process. Positional cloning identified BOR1 as a membrane protein with homology to bicarbonate transporters in animals. Moreover, a fusion protein of BOR1 and green fluorescent protein (GFP) localized to the plasma membrane in transformed cells. The promoter of BOR1 drove GFP expression in root pericycle cells. When expressed in yeast, BOR1 decreased boron concentrations in cells. We show here that BOR1 is an efflux-type boron transporter for xylem loading and is essential for protecting shoots from boron deficiency.
authors.affiliation: Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
authors.forename: Junpei
authors.initials: J
authors.lastname: Takano
authors.forename: Kyotaro
authors.initials: K
authors.lastname: Noguchi
authors.forename: Miho
authors.initials: M
authors.lastname: Yasumori
authors.forename: Masaharu
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Zofia
authors.initials: Z
authors.lastname: Gajdos
authors.forename: Kyoko
authors.initials: K
authors.lastname: Miwa
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Hayashi
authors.forename: Tadakatsu
authors.initials: T
authors.lastname: Yoneyama
authors.forename: Toru
authors.initials: T
authors.lastname: Fujiwara
mesh_terms: D000595:Amino Acid Sequence; D017920:Antiporters / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000033:anatomy & histology / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D001895:Boron / Q000172:deficiency / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D009154:Mutation; D018517:Plant Roots / Q000033:anatomy & histology / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D018520:Plant Shoots / Q000033:anatomy & histology / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D017385:Sequence Homology; D014934:Wood
chemical_list: D017920:Antiporters; D029681:Arabidopsis Proteins; C469216:BOR1 protein, Arabidopsis; D002352:Carrier Proteins; D001895:Boron