title: Amino Acid Export in Developing Arabidopsis Seeds Depends on UmamiT Facilitators.
abstract: Essential amino acids cannot be synthesized by humans and animals. They often are limiting in plant-derived foods and determine the nutritional value of a given diet. Seeds and fruits often represent the harvestable portion of plants. In order to improve the amino acid composition of these tissues, it is indispensable to understand how these substrates are transported within the plant. Amino acids result from nitrogen assimilation, which often occurs in leaves, the source tissue. They are transported via the vasculature, the xylem, and the phloem into the seeds, the so-called sink tissue, where they are stored or consumed. In seeds, several tissues are symplasmically isolated, i.e., not connected by plasmodesmata, channels in the cell walls that enable a cytoplasmic continuum in plants. Consequently, amino acids must be exported from cells into the apoplast and re-imported many times to support seed development. Several amino acid importers are known, but exporters remained elusive. Here, we characterize four members of the plant-specific UmamiT transporter family from Arabidopsis, related to the amino acid facilitator SIAR1 and the vacuolar auxin transporter WAT1. We show that the proteins transport amino acids along their (electro)chemical potential across the plasma membrane. In seeds, they are found in tissues from which amino acids are exported. Loss-of-function mutants accumulate high levels of free amino acids in fruits and produce smaller seeds. Our results strongly suggest a crucial role for the UmamiTs in amino acid export and possibly a means to improve yield quality.
authors.affiliation: Cell Biology and Plant Biochemistry, Regensburg University, Universitätsstrasse 31, 93053 Regensburg, Germany.
authors.forename: Benedikt
authors.initials: B
authors.lastname: Müller
authors.affiliation: Cell Biology and Plant Biochemistry, Regensburg University, Universitätsstrasse 31, 93053 Regensburg, Germany.
authors.forename: Astrid
authors.initials: A
authors.lastname: Fastner
authors.affiliation: Cell Biology and Plant Biochemistry, Regensburg University, Universitätsstrasse 31, 93053 Regensburg, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Karmann
authors.affiliation: Cell Biology and Plant Biochemistry, Regensburg University, Universitätsstrasse 31, 93053 Regensburg, Germany.
authors.forename: Verena
authors.initials: V
authors.lastname: Mansch
authors.affiliation: Biotechnology of Natural Compounds, Technical University Munich, Liesel-Beckmann-Strasse 1, 85354 Freising, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Hoffmann
authors.affiliation: Biotechnology of Natural Compounds, Technical University Munich, Liesel-Beckmann-Strasse 1, 85354 Freising, Germany.
authors.forename: Wilfried
authors.initials: W
authors.lastname: Schwab
authors.affiliation: Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013 Bern, Switzerland.
authors.forename: Marianne
authors.initials: M
authors.lastname: Suter-Grotemeyer
authors.affiliation: Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013 Bern, Switzerland.
authors.forename: Doris
authors.initials: D
authors.lastname: Rentsch
authors.affiliation: Institute of Plant Sciences, ETH Zürich, Universitätstrasse 2, 8092 Zürich, Switzerland.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Truernit
authors.affiliation: Zentrum für Molekularbiologie der Pflanzen (ZMBP), Universität Tübingen, Auf der Morgenstelle 32, 72076 Tübingen, Germany.
authors.forename: Friederike
authors.initials: F
authors.lastname: Ladwig
authors.affiliation: Cell Biology and Plant Biochemistry, Regensburg University, Universitätsstrasse 31, 93053 Regensburg, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Bleckmann
authors.affiliation: Cell Biology and Plant Biochemistry, Regensburg University, Universitätsstrasse 31, 93053 Regensburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Dresselhaus
authors.affiliation: Cell Biology and Plant Biochemistry, Regensburg University, Universitätsstrasse 31, 93053 Regensburg, Germany. Electronic address: ulrich.hammes@biologie.uni-regensburg.de.
authors.forename: Ulrich Z
authors.initials: UZ
authors.lastname: Hammes
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D012639:Seeds / Q000254:growth & development / Q000378:metabolism; D014018:Tissue Distribution
chemical_list: D000596:Amino Acids; D029681:Arabidopsis Proteins; D026901:Membrane Transport Proteins