Molecular identification and physiological characterization of a novel monosaccharide transporter from Arabidopsis involved in vacuolar sugar transport.
The tonoplast monosaccharide transporter (TMT) family comprises three isoforms in Arabidopsis thaliana, and TMT-green fluorescent protein fusion proteins are targeted to the vacuolar membrane. TMT promoter-beta-glucuronidase plants revealed that the TONOPLAST MONOSACCHARIDE TRANSPORTER1 (TMT1) and TMT2 genes exhibit a tissue- and cell type-specific expression pattern, whereas TMT3 is only weakly expressed. TMT1 and TMT2 expression is induced by drought, salt, and cold treatments and by sugar. During cold adaptation, tmt knockout lines accumulated less glucose and fructose compared with wild-type plants, whereas no differences were observed for sucrose. Cold adaptation of wild-type plants substantially promoted glucose uptake into isolated leaf mesophyll vacuoles. Glucose uptake into isolated vacuoles was inhibited by NH(4)(+), fructose, and phlorizin, indicating that transport is energy-dependent and that both glucose and fructose were taken up by the same carrier. Glucose import into vacuoles from two cold-induced tmt1 knockout lines or from triple knockout plants was substantially lower than into corresponding wild-type vacuoles. Monosaccharide feeding into leaf discs revealed the strongest response to sugar in tmt1 knockout lines compared with wild-type plants, suggesting that TMT1 is required for cytosolic glucose homeostasis. Our results indicate that TMT1 is involved in vacuolar monosaccharide transport and plays a major role during stress responses.
Wormit
Alexandra
A
Pflanzenphysiologie, Technische Universität Kaiserslautern, D-67653 Kaiserslautern, Germany.
Trentmann
Oliver
O
Feifer
Ingmar
I
Lohr
Christian
C
Tjaden
Joachim
J
Meyer
Stefan
S
Schmidt
Ulrike
U
Martinoia
Enrico
E
Neuhaus
H Ekkehard
HE
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000166:cytology / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D003080:Cold Temperature; D004269:DNA, Bacterial; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006720:Homozygote; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009005:Monosaccharides / Q000378:metabolism* / Q000494:pharmacology; D009154:Mutation / Q000235:genetics; D009928:Organ Specificity / Q000187:drug effects; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D011523:Protoplasts / Q000166:cytology / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D014617:Vacuoles / Q000187:drug effects / Q000378:metabolism*
D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; D009004:Monosaccharide Transport Proteins; D009005:Monosaccharides; D012333:RNA, Messenger; C036483:T-DNA; C518496:Tmt1 protein, Arabidopsis; C518497:Tmt2 protein, Arabidopsis; C518498:Tmt3 protein, Arabidopsis