Expression analysis and functional characterization of the monosaccharide transporters, OsTMTs, involving vacuolar sugar transport in rice (Oryza sativa).
In Arabidopsis, the compartmentation of sugars into vacuoles is known to be facilitated by sugar transporters. However, vacuolar sugar transporters have not been studied in detail in other plant species. To characterize the rice (Oryza sativa) tonoplast monosaccharide transporters, OsTMT1 and OsTMT2, we analysed their subcellular localization using green fluorescent protein (GFP) and expression patterns using reverse-transcription polymerase chain reaction (RT-PCR), performed histochemical beta-glucuronidase (GUS) assay and in situ hybridization analysis, and assessed sugar transport ability using isolated vacuoles. Expression of OsTMT-GFP fusion protein in rice and Arabidopsis revealed that the OsTMTs localize at the tonoplast. Analyses of OsTMT promoter-GUS transgenic rice indicated that OsTMT1 and OsTMT2 are highly expressed in bundle sheath cells, and in vascular parenchyma and companion cells in leaves, respectively. Both genes were found to be preferentially expressed in the vascular tissues of roots, the palea/lemma of spikelets, and in the main vascular tissues and nucellar projections on the dorsal side of the seed coats. Glucose uptake studies using vacuoles isolated from transgenic mutant Arabidopsis (tmt1-2-3) expressing OsTMT1 demonstrated that OsTMTs are capable of transporting glucose into vacuoles. Based on expression analysis and functional characterization, our present findings suggest that the OsTMTs play a role in vacuolar glucose storage in rice.
Cho
Jung-Il
JI
Graduate School of Biotechnology and Plant Metabolism Research Center, Kyung Hee University, Yongin 446-701, Korea.
Burla
Bo
B
Lee
Dae-Woo
DW
Ryoo
Nayeon
N
Hong
Soon-Kwan
SK
Kim
Hyun-Bi
HB
Eom
Joon-Seob
JS
Choi
Sang-Bong
SB
Cho
Man-Ho
MH
Bhoo
Seong Hee
SH
Hahn
Tae-Ryong
TR
Neuhaus
H Ekkehard
HE
Martinoia
Enrico
E
Jeon
Jong-Seong
JS
D017360:Arabidopsis / Q000235:genetics; D001692:Biological Transport; D050260:Carbohydrate Metabolism; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D005947:Glucose / Q000378:metabolism; D005966:Glucuronidase / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D009928:Organ Specificity; D012275:Oryza / Q000166:cytology / Q000235:genetics*; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D014617:Vacuoles / Q000378:metabolism*
D026901:Membrane Transport Proteins; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D005966:Glucuronidase; D005947:Glucose