Monosaccharides transporters play important roles in assimilate supply for sink tissue development. In this study, a new monosaccharide transporter gene OsMST6 was identified from rice (Oryza sativa L.). The predicted OsMST6 protein shows typical features of sugar transporters and shares 79.6% identity with the rice monosaccharide transporter OsMST3. Heterologous expression in yeast (Saccharomyces cerevisiae) demonstrated that OsMST6 is a broad-spectrum monosaccharide transporter, with a K m of 266.1 μΜ for glucose. OsMST6-green fluorescent protein fusion protein is localized to the plasma membrane in plant. Semi-quantitative RT-PCR analysis exhibited that OsMST6 is expressed in all tested organs/tissues. In developing seeds, OsMST6 expression level is high at the early and middle grain filling stages and gradually declines later. Further analysis detected its expression in both maternal and filial tissues. RNA in situ hybridization analysis indicated that OsMST6 is predominantly expressed in the vascular parenchyma of the chalazal vein, cross-cells, nucellar tissue and endosperm of young seeds, in mesophyll cells of source leaf blades, and in pollens and the connective vein of anthers. In addition, OsMST6 expression is up-regulated by salt stress and sugars. The physiological role of OsMST6 for seed development and its roles in other sink and source tissues are discussed.
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Acknowledgments We thank Dr. Eckhard Boles (Heinrich-Heine-Universität, Düsseldorf, Germany) for providing the S. cerevisiae strain EBY.VW4000 and Dr. Michael Büttner (Universität Erlangen-Nürn-berg, Erlangen, Germany) for providing the S. cerevisiae/E. coli shuttle vector pEX-Tag. This work is supported by grants from the National Hi-tech Research and Development Program (2006AA10A101), the Knowledge Innovation Program of Chinese Academy of Science (KSCX1-YW-03), the Programme for Strategic ScientiWc Alliances (04-PSA-BD-04) between China and the Netherlands of the Royal Netherlands Academy of Arts and Sciences (KNAW) for P.B.F.O. and M.W., and the KNAW China Exchange Programme (04CDP022) for Y.X. and the CAS KNAW Joint PhD Training Programme (05-PhD-02) for Y.Z.
- Expression pattern
- Monosaccharide transporter
- Seed development
- cDNA cloning