title: The Arabidopsis vacuolar sugar transporter SWEET2 limits carbon sequestration from roots and restricts Pythium infection.
abstract: Plant roots secrete a significant portion of their assimilated carbon into the rhizosphere. The putative sugar transporter SWEET2 is highly expressed in Arabidopsis roots. Expression patterns of SWEET2-β-glucuronidase fusions confirmed that SWEET2 accumulates highly in root cells and thus may contribute to sugar secretion, specifically from epidermal cells of the root apex. SWEET2-green fluorescent protein fusions localized to the tonoplast, which engulfs the major sugar storage compartment. Functional analysis of SWEET2 activity in yeast showed low uptake activity for the glucose analog 2-deoxyglucose, consistent with a role in the transport of glucose across the tonoplast. Loss-of-function sweet2 mutants showed reduced tolerance to excess glucose, lower glucose accumulation in leaves, and 15-25% higher glucose-derived carbon efflux from roots, suggesting that SWEET2 has a role in preventing the loss of sugar from root tissue. SWEET2 root expression was induced more than 10-fold during Pythium infection. Importantly, sweet2 mutants were more susceptible to the oomycete, showing impaired growth after infection. We propose that root-expressed vacuolar SWEET2 modulates sugar secretion, possibly by reducing the availability of glucose sequestered in the vacuole, thereby limiting carbon loss to the rhizosphere. Moreover, the reduced availability of sugar in the rhizosphere due to SWEET2 activity contributes to resistance to Pythium.
authors.affiliation: Institute of Tropical Plant Science, National Cheng Kung University, Tainan City, 7013, Taiwan.
authors.forename: Hsin-Yi
authors.initials: HY
authors.lastname: Chen
authors.affiliation: Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24061, USA.
authors.forename: Jung-Hyun
authors.initials: JH
authors.lastname: Huh
authors.affiliation: Institute of Tropical Plant Science, National Cheng Kung University, Tainan City, 7013, Taiwan.
authors.forename: Ya-Chi
authors.initials: YC
authors.lastname: Yu
authors.affiliation: Institute of Tropical Plant Science, National Cheng Kung University, Tainan City, 7013, Taiwan.
authors.forename: Li-Hsuan
authors.initials: LH
authors.lastname: Ho
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, CA, 94305, USA.
authors.forename: Li-Qing
authors.initials: LQ
authors.lastname: Chen
authors.affiliation: Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24061, USA.
authors.forename: Dorothea
authors.initials: D
authors.lastname: Tholl
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, CA, 94305, USA.
authors.forename: Wolf B
authors.initials: WB
authors.lastname: Frommer
authors.affiliation: Institute of Tropical Plant Science, National Cheng Kung University, Tainan City, 7013, Taiwan.|Department of Plant Biology, Carnegie Institution for Science, Stanford, CA, 94305, USA.
authors.forename: Woei-Jiun
authors.initials: WJ
authors.lastname: Guo
mesh_terms: D017360:Arabidopsis / Q000382:microbiology / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D057965:Carbon Sequestration; D018506:Gene Expression Regulation, Plant; D005947:Glucose / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D054884:Host-Pathogen Interactions; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D010935:Plant Diseases / Q000382:microbiology*; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism* / Q000382:microbiology; D030821:Plants, Genetically Modified; D011775:Pythium / Q000472:pathogenicity*; D014617:Vacuoles / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D009004:Monosaccharide Transport Proteins; C000608383:SWEET2 protein, Arabidopsis; D049452:Green Fluorescent Proteins; D005947:Glucose
keywords: Arabidopsis thaliana; SWEET; carbon sequestration; pathogen resistance; plant-microbe interactions; rhizosphere; sugar efflux; sugar homeostasis; tonoplast transport