title: Macromolecular trafficking indicated by localization and turnover of sucrose transporters in enucleate sieve elements.
abstract: The leaf sucrose transporter SUT1 is essential for phloem loading and long-distance transport of assimilates. Both SUT1 messenger RNA (mRNA) and protein were shown to be diurnally regulated and to have high turnover rates. SUT1 protein was detected by immunolocalization in plasma membranes of enucleate sieve elements (SEs) in tobacco, potato, and tomato. Analysis by in situ hybridization showed that SUT1 mRNA localizes mainly to the SE and is preferentially associated with plasmodesmata. Antisense inhibition of SUT1 expression under control of a companion cell (CC)-specific promoter indicated synthesis of SUT1 mRNA in the CC. These results provide evidence for targeting of plant endogenous mRNA and potentially SUT1 protein through phloem plasmodesmata and for sucrose loading at the plasma membrane of SE.
authors.affiliation: Institut für Botanik, Eberhard-Karls-Universität, Auf der Morgenstelle 1, D-72076 Tübingen, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Kühn
authors.forename: V R
authors.initials: VR
authors.lastname: Franceschi
authors.forename: A
authors.initials: A
authors.lastname: Schulz
authors.forename: R
authors.initials: R
authors.lastname: Lemoine
authors.forename: W B
authors.initials: WB
authors.lastname: Frommer
mesh_terms: D000595:Amino Acid Sequence; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D018551:Solanum lycopersicum / Q000378:metabolism; D008565:Membrane Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D018515:Plant Leaves / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D010940:Plant Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D010947:Plants, Toxic; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D011198:Solanum tuberosum; D013395:Sucrose / Q000378:metabolism; D014026:Nicotiana / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D010940:Plant Proteins; D012333:RNA, Messenger; D018749:RNA, Plant; C078729:sucrose transport protein, plant; D013395:Sucrose