title: Molecular Characterization of LjSWEET3, a Sugar Transporter in Nodules of Lotus japonicus.
abstract: Symbiotic nitrogen fixation in legumes contributes greatly to the global nitrogen cycle on the earth. In nodules, resident rhizobia supply nitrogen nutrient fixed from atmospheric N2 to the host plant; in turn, the plant provides photosynthetic metabolites to bacteroids as a carbon source. In this process, various transporters are involved at different membrane systems; however, little is known at the molecular level about the flow of carbon from the host cells to the symbiotic bacteria. We have been studying transporters functioning in nodules of Lotus japonicus, and found that out of 13 SWEET genes in the L. japonicus genome LjSWEET3, a member of the SWEET transporter family, is highly expressed in nodules. The SWEET family was first identified in Arabidopsis, where members of the family are involved in phloem loading, nectar secretion, pollen nutrition and seed filling. The expression of LjSWEET3 strongly increased during nodule development and reached the highest level in mature nodules. Histochemical analysis using L. japonicus plants transformed with LjSWEET3 promoter:GUS (β-glucuronidase) showed strong expression in the vascular systems of nodules. Analysis of an LjSWEET3-green fluorescent protein (GFP) fusion expressed in Nicotiana banthamiana and Coptis japonica indicates that LjSWEET3 localizes to the plasma membrane. Together these data are consistent with a role for LjSWEET3 in sugar translocation towards nodules and also suggest the possible existence of multiple routes of carbon supply into nodules.
authors.affiliation: Laboratory of Plant Gene Expression, Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Japan.
authors.forename: Akifumi
authors.initials: A
authors.lastname: Sugiyama
authors.affiliation: Laboratory of Plant Gene Expression, Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Saida
authors.affiliation: Laboratory of Plant Gene Expression, Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Japan.
authors.forename: Mayuko
authors.initials: M
authors.lastname: Yoshimizu
authors.affiliation: Laboratory of Plant Gene Expression, Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Japan.|Institute of Mountain Science, Shinshu University, Matsumoto, Japan.
authors.forename: Kojiro
authors.initials: K
authors.lastname: Takanashi
authors.affiliation: Department of Plant Biology, Carnegie Institution of Science, Stanford, CA , USA.
authors.forename: Davide
authors.initials: D
authors.lastname: Sosso
authors.affiliation: Department of Plant Biology, Carnegie Institution of Science, Stanford, CA , USA.
authors.forename: Wolf B
authors.initials: WB
authors.lastname: Frommer
authors.affiliation: Laboratory of Plant Gene Expression, Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Japan.
authors.forename: Kazufumi
authors.initials: K
authors.lastname: Yazaki
mesh_terms: D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology; D000070116:Lotus / Q000235:genetics / Q000378:metabolism*; D009586:Nitrogen Fixation / Q000235:genetics / Q000502:physiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D053204:Root Nodules, Plant / Q000235:genetics / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D013395:Sucrose
keywords: Lotus japonicus; Nodule; SWEET; Sucrose