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•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 β-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. [ABSTRACT FROM AUTHOR]

In higher plants, the plastidic glucose translocator (pGlcT) is assumed to play a role in the export of starch degradation products, but this has not yet been studied in detail. To elucidate the role of pGlcT in the leaves of Arabidopsis thaliana, we generated single and double mutants lacking three plastidic sugar transporters, pGlcT, the triose-phosphate / phosphate translocator (TPT), and the maltose transporter (MEX1), and analyzed their growth phenotypes, photosynthetic properties and metabolite contents. In contrast to the pglct-1 and pglct-2 single mutants lacking a visible growth phenotype, the double mutants pglct-1 / mex1 and tpt-2 / mex1 displayed markedly inhibited plant growth. Notably, pglct-1 / mex1 exhibited more severe growth retardation than that seen for the other mutants. In parallel, the most severe reductions in sucrose content and starch turnover were observed in the pglct- 1 / mex1 mutant. The concurrent loss of pGlcT and MEX1 also resulted in severely reduced photosynthetic activities and extreme chloroplast abnormalities. These findings suggest that pGlcT, together with MEX1, contributes significantly to the export of starch degradation products from chloroplasts in A. thaliana leaves, and that this starch-mediated pathway for photoassimilate export via pGlcT and MEX1 is essential for the growth and development of A. thaliana. [ABSTRACT FROM AUTHOR]