title: Nectar secretion requires sucrose phosphate synthases and the sugar transporter SWEET9.
abstract: Angiosperms developed floral nectaries that reward pollinating insects. Although nectar function and composition have been characterized, the mechanism of nectar secretion has remained unclear. Here we identify SWEET9 as a nectary-specific sugar transporter in three eudicot species: Arabidopsis thaliana, Brassica rapa (extrastaminal nectaries) and Nicotiana attenuata (gynoecial nectaries). We show that SWEET9 is essential for nectar production and can function as an efflux transporter. We also show that sucrose phosphate synthase genes, encoding key enzymes for sucrose biosynthesis, are highly expressed in nectaries and that their expression is also essential for nectar secretion. Together these data are consistent with a model in which sucrose is synthesized in the nectary parenchyma and subsequently secreted into the extracellular space via SWEET9, where sucrose is hydrolysed by an apoplasmic invertase to produce a mixture of sucrose, glucose and fructose. The recruitment of SWEET9 for sucrose export may have been a key innovation, and could have coincided with the evolution of core eudicots and contributed to the evolution of nectar secretion to reward pollinators.
authors.affiliation: 1] Department of Biology, Stanford University, Stanford, California 94305, USA [2] Carnegie Institution for Science, 260 Panama Street, Stanford, California 94305, USA.
authors.forename: I Winnie
authors.initials: IW
authors.lastname: Lin
authors.affiliation: 1] Department of Biology, Stanford University, Stanford, California 94305, USA [2] Carnegie Institution for Science, 260 Panama Street, Stanford, California 94305, USA.
authors.forename: Davide
authors.initials: D
authors.lastname: Sosso
authors.affiliation: Carnegie Institution for Science, 260 Panama Street, Stanford, California 94305, USA.
authors.forename: Li-Qing
authors.initials: LQ
authors.lastname: Chen
authors.affiliation: Max Planck Institute for Chemical Ecology, Jena D-07745, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Gase
authors.affiliation: Max Planck Institute for Chemical Ecology, Jena D-07745, Germany.
authors.forename: Sang-Gyu
authors.initials: SG
authors.lastname: Kim
authors.affiliation: Max Planck Institute for Chemical Ecology, Jena D-07745, Germany.
authors.forename: Danny
authors.initials: D
authors.lastname: Kessler
authors.affiliation: 1] Department of Biology, University of Minnesota Duluth, Duluth, Minnesota 55812, USA [2] Department of Plant Biology, University of Minnesota, St Paul, Minnesota 55108, USA.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Klinkenberg
authors.affiliation: 1] Department of Biology, University of Minnesota Duluth, Duluth, Minnesota 55812, USA [2] Department of Plant Biology, University of Minnesota, St Paul, Minnesota 55108, USA.
authors.forename: Molly K
authors.initials: MK
authors.lastname: Gorder
authors.affiliation: Carnegie Institution for Science, 260 Panama Street, Stanford, California 94305, USA.
authors.forename: Bi-Huei
authors.initials: BH
authors.lastname: Hou
authors.affiliation: 1] Carnegie Institution for Science, 260 Panama Street, Stanford, California 94305, USA [2] Key Laboratory of Plant and Soil Interactions, College of Resources and Environmental Sciences, China Agricultural University, 100193 Beijing, China.
authors.forename: Xiao-Qing
authors.initials: XQ
authors.lastname: Qu
authors.affiliation: 1] Department of Biology, University of Minnesota Duluth, Duluth, Minnesota 55812, USA [2] Department of Plant Biology, University of Minnesota, St Paul, Minnesota 55108, USA.
authors.forename: Clay J
authors.initials: CJ
authors.lastname: Carter
authors.affiliation: Max Planck Institute for Chemical Ecology, Jena D-07745, Germany.
authors.forename: Ian T
authors.initials: IT
authors.lastname: Baldwin
authors.affiliation: 1] Department of Biology, Stanford University, Stanford, California 94305, USA [2] Carnegie Institution for Science, 260 Panama Street, Stanford, California 94305, USA.
authors.forename: Wolf B
authors.initials: WB
authors.lastname: Frommer
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000378:metabolism; D000818:Animals; D017360:Arabidopsis / Q000166:cytology / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism; D029741:Brassica rapa / Q000033:anatomy & histology / Q000201:enzymology / Q000378:metabolism; D050260:Carbohydrate Metabolism; D005110:Extracellular Space / Q000378:metabolism; D035264:Flowers / Q000502:physiology; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D026901:Membrane Transport Proteins / Q000378:metabolism; D009865:Oocytes; D057048:Plant Nectar / Q000096:biosynthesis / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D054817:Pollination; D021381:Protein Transport; D017385:Sequence Homology; D013213:Starch / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism*; D014026:Nicotiana / Q000033:anatomy & histology / Q000201:enzymology / Q000378:metabolism; D014981:Xenopus; D043324:beta-Fructofuranosidase / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D026901:Membrane Transport Proteins; D057048:Plant Nectar; D010940:Plant Proteins; C569467:SWEET12 protein, Arabidopsis; D013395:Sucrose; D013213:Starch; D005964:Glucosyltransferases; C022698:sucrose-phosphate synthase; D019883:Alkyl and Aryl Transferases; C500830:SPS1 protein, Arabidopsis; C500831:SPS2 protein, Arabidopsis; D043324:beta-Fructofuranosidase