Expression analysis and functional characterization of the monosaccharide transporters, OsTMTs, involving vacuolar sugar transport in rice (Oryza sativa)

Abstract

Summary• 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 b-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 Os-TMT1 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.

Impaired Function of the Tonoplast-Localized Sucrose Transporter in Rice, OsSUT2, Limits the Transport of Vacuolar Reserve Sucrose and Affects Plant Growth

“…The tonoplast monosaccharide transporters (TMTs) have been characterized in Arabidopsis (Wormit et al, 2006;Wingenter et al, 2010) and rice (Cho et al, 2010) and are thought to function in the transport of monosaccharides, Glc and Fru, from the cytosol to the vacuole lumen using a H + -sugar antiport mechanism. Based on their expression patterns, the Arabidopsis TMTs are thought to play a major role in osmotic stress responses, whereas rice TMTs mainly function in sugar retrieval during sugar translocation.…”

“…Various tissues from pOsSUT2::GUS transgenic plants were collected and stained in GUS reaction solution containing 0.2 M sodium phosphate (pH 7.0), 10 mM EDTA, 20% methanol, 2% dimethyl sulfoxide, and 0.1% 5-bromo-4-chloro-3-indole-b-glucuronide, as described previously by Cho et al (2010). Briefly, samples were incubated at 37°C overnight and then transferred to 70% ethanol to remove chlorophyll.…”

Sucrose Transporter Localization and Function in Phloem Unloading in Developing Stems

“…TSTs are capable of transporting Suc into rice, Arabidopsis, and sugar beet vacuoles (Cho et al, 2010; A, SbSUT1 at pH 5.6. B, SbSUT1 at pH 7.…”

Identification and Characterization of the Duplicate Rice Sucrose Synthase Genes OsSUS5 and OsSUS7 Which Are Associated with the Plasma Membrane

“…protoplasts were stained with a lipophilic styryl dye, FM4-64, which primarily stains the plasma membrane (Cho et al, 2010;Ueda et al, 2001;Uemura et al, 2004). The GFP signals were indeed well merged with those of FM4-64 in the plasma membrane (Figs.…”