title: Rhizosecretion of stele-synthesized glucosinolates and their catabolites requires GTR-mediated import in Arabidopsis.
abstract: Casparian strip-generated apoplastic barriers not only control the radial flow of both water and ions but may also constitute a hindrance for the rhizosecretion of stele-synthesized phytochemicals. Here, we establish root-synthesized glucosinolates (GLS) are in Arabidopsis as a model to study the transport routes of plant-derived metabolites from the site of synthesis to the rhizosphere. Analysing the expression of GLS synthetic genes in the root indicate that the stele is the major site for the synthesis of aliphatic GLS, whereas indole GLS can be synthesized in both the stele and the cortex. Sampling root exudates from the wild type and the double mutant of the GLS importers GTR1 and GTR2 show that GTR-mediated retention of stele-synthesized GLS is a prerequisite for the exudation of both intact GLS and their catabolites into the rhizosphere. The expression of the GTRs inside the stele, combined with the previous observation that GLS are exported from biosynthetic cells, suggest three possible routes of stele-synthesized aliphatic GLS after their synthesis: (i) GTR-dependent import to cells symplastically connected to the cortical cells and the rhizosphere; (ii) GTR-independent transport via the xylem to the shoot; and (iii) GTR-dependent import to GLS-degrading myrosin cells at the cortex. The study suggests a previously undiscovered role of the import process in the rhizosecretion of root-synthesized phytochemicals.
authors.affiliation: DynaMo Center, Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark.
authors.forename: Deyang
authors.initials: D
authors.lastname: Xu
authors.affiliation: Department of Plant Quality, Leibniz Institute of Vegetable and Ornamental Crops, Theodor-Echtermeyer-Weg 1, 14979 Grossbeeren, Germany.
authors.forename: Franziska S
authors.initials: FS
authors.lastname: Hanschen
authors.affiliation: Department of Plant Health, Leibniz Institute of Vegetable and Ornamental Crops, Theodor-Echtermeyer-Weg 1, 14979 Grossbeeren, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Witzel
authors.affiliation: DynaMo Center, Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark.
authors.forename: Sebastian J
authors.initials: SJ
authors.lastname: Nintemann
authors.affiliation: DynaMo Center, Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark.
authors.forename: Hussam Hassan
authors.initials: HH
authors.lastname: Nour-Eldin
authors.affiliation: Department of Plant Quality, Leibniz Institute of Vegetable and Ornamental Crops, Theodor-Echtermeyer-Weg 1, 14979 Grossbeeren, Germany.
authors.forename: Monika
authors.initials: M
authors.lastname: Schreiner
authors.affiliation: DynaMo Center, Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark.
authors.forename: Barbara Ann
authors.initials: BA
authors.lastname: Halkier
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001692:Biological Transport; D005961:Glucosinolates / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C575185:GTR1 protein, Arabidopsis; C575186:GTR2 protein, Arabidopsis; D005961:Glucosinolates; D009004:Monosaccharide Transport Proteins
keywords: Arabidopsis; GTR; biosynthesis; exudate; glucosinolates (GLS); glucosinolates catabolites; import; rhizosecretion; rhizosphere; stele-synthesized phytochemicals; trans-cellular transport