Os12g0641400

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Gene Os12g0641400,namely OsSUT2,means sucrose transporter.

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Annotated Information

Function

  • OsSUT2 (Os12g0641400) The ossut2 mutant exhibited a growth retardation phenotype with a significant reduction in tiller number, plant height, 1,000-grain weight, and root dry weight compared with the controls, the wild type, and complemented transgenic lines. Analysis of primary carbon metabolites revealed that ossut2 accumulated more Suc, glucose, and fructose in the leaves than the controls. Further sugar export analysis of detached leaves indicated that ossut2 had a significantly decreased sugar export ability compared with the controls. These results suggest that OsSUT2 is involved in Suc transport across the tonoplast from the vacuole lumen to the cytosol in rice, playing an essential role in sugar export from the source leaves to sink organs.[1]

  • The OsSUT2 cDNA (accession no. HQ875341) encodes a protein of 501 amino acids in length. According to membrane protein topology prediction using Hidden Markov Models in TMMOD software [2], the OsSUT2 protein contains 12 transmembrane domains.[1]
  • Results of Suc transport assays in yeast were consistent with a H + -Sucsymport mechanism, suggesting that OsSUT2 functions in Suc uptake from the vacuole.[3].

  • OsSUT2 is involved in Suc transport across the tonoplast from the vacuole lumen to the cytosol in rice, playing an essential role in sugar export from the source leaves to sink organs.[4].

Expression Pattern

  • In embryos of germinating seeds, the expression of OsSUT2 gradually increased during the early germinating stage. The developmental regulations of OsSUT2 in germinating embryos could be mediated by sugars transported from endosperms. OsSUT2 expression was up-regulated by glucose through a hexokinase-independent pathway.[1]

  • Based on OsSUT2 promoter::GUS expression in germinating seeds of transgenic rice, OsSUT2 was signifi-cantly expressed in the embryos and aleurone layers. In embryos, strong GUS expression was detected in the scutellum and vascular bundle tissues. Developmental stage- and sugar-dependent OsSUT2 expression was suggested to be controlled by transcriptional regulation of the promoter region.[1]

  • Expression of OsSUT2-green fluorescent protein in rice revealed that OsSUT2 localizes to the tonoplast. Analysis of the OsSUT2 promoter::b-glucuronidase transgenic rice indicated that this gene is highly expressed in leaf mesophyll cells, emerging lateral roots, pedicels of fertilized spikelets, and cross cell layers of seed coats.(Figure 1)[3]

Figure 1. Changes in OsSUT2 expression in embryos during seed germination. The data are presented as mean±SD.[1]
  • Carbohydrate transport from endosperms and embryos to coleoptiles, shoots, and roots is an important process for supplying developing tissues with a carbon source during seed germination and seedling establishment. The levels of OsSUT2 mRNA gradually increased from 1 to 5 DAI.(Figure 1.)[1]

Evolution

  • Based on a previous phylogenetic analysis of the SUT gene family by Braun and Slewinski, OsSUT2 was grouped with Arabidopsis. AtSUT4 is also classified with StSUT4 and LeSUT4 in the same group. The amino acid identities between OsSUT2 and StSUT4, LeSUT4, and AtSUT4 are 66%, 66%, and 64%.[1]
  • In the plant SUT protein family, OsSUT1, 3, 4 and 5 are clustered together with members of the dicot-SUT2 group, forming the Type-II subfamily. Within this subfamily OsSUT1 and the orthologues from other cereal species form the cereal (monocot) -SUT1 group, sharing at least 80% identity to one another. OsSUT3 and OsSUT5 are mapped separately in the Type-II subfamily. OsSUT4 seems to be the rice orthologue of the dicot-SUT2 proteins, sharing 58–63% identity and the common features of an extended N-terminal and central loop. OsSUT2, together with HvSUT2, is closely related to dicot-SUT4 group, forming the Type-III subfamily.(Figure 2)[3]
Figure 2. An un-rooted dendrogram of plant SUTs, based on deduced amino acid sequences. The CLUSTALW program was used to show the relationship between the members of the OsSUT gene family (bold) and other plant SUTs.[1]

Subcellular localization

  • OsSUT2 encodes a putative sucrose transporter containing 12 transmembrane domains in rice plants. Subcellular localization of the OsSUT2::GFP fusion protein indicated that OsSUT2 is a cell membrane protein(Figure 3,4).[1]
    Figure 3. Alignment of amino acid sequences from potato SUT4 (StSUT4; Genbank accession AF237780), tomato SUT4 (LeSUT4; AF176950), Arabidopsis SUT4 (AtSUT4; AY072092), and rice OsSUT2 (HQ875341). TM transmembrane domain. [1].
Figure 4. Comparison of SUT protein structures. The inside and outside membrane regions and transmembrane domains of OsSUT2, StSUT4, AtSUT4, LeSUT4, AtSUT2 (AK226970), and LeSUT2 (AF166498) were predicted using TMMOD software. [1].
  • The expression of OsSUT2-GFP fusion protein was observed in the aleurone layer cells of barley seeds. Fluorescence imaging showed that the fusion protein was localized on the plasma membrane.(Figure 5)[1]
Figure 5. Subcellular localization of OsSUT2 by transient expression of OsSUT2-GFP fusion proteins in barley aleurone layer cells. a Bright field image. b GFP fluorescence image. c Merged field and fluorescence image. [1].
  • OsSUT2 contains 12 transmembrane domains and was localized on plasma membrane. Amino acid alignment showed that the number of amino acids in the central inside loops are similar among OsSUT2 and other SUTs in group 4. The length of the OsSUT2 central loop is shorter than that of SUTs belonging to group 2, i.e., AtSUT2 and LeSUT2. LeSUT2 is considered to function as a putative sucrose sensor.[1]

Knowledge Extension

  • SUT proteins are important carriers for transporting sucrose across the plasma membrane or vacuolar membranes. Arabidopsis SUT protein has also been found on the chloroplast membrane. Rice OsSUT2 is classified in the same group with Arabidopsis AtSUT4, tomato LeSUT4, potato StSUT4, Lotus japonicus LjSUT4, and barley HvSUT2. Some of the above-mentioned SUTs, including AtSUT4, StSUT4, and LjSUT4, have been identified as low-affinity/high-capacity transporters.

Labs working on this gene

  • Naohiro Aoki, Graham N. Scofield, Paul R. Whitfeld:CSIRO Plant Industry, Canberra, ACT, 2601 Australia
  • Tatsuro Hirose: Department of Rice Research, National Agricultural Research Center, Joetsu, Niigata, 943-0193 Japan
  • Naohiro Aoki, Tatsuro Hirose: These authors have contributed equally to this work and should be considered as joint first authors
  • Robert T. Furbank: Corresponding author: Email, robert.furbank@csiro.au; Fax, +61-2-6246-5000
  • Joon-Seob Eom, Jung-Il Cho: Graduate School of Biotechnology and Plant Metabolism Research Center
  • Sang-Won Lee, Youngchul Yoo, Gynheung An: Department of Plant Molecular Systems Biotechnology
  • Joon-Seob Eom, Jung-Il Cho, Sang-Won Lee, Youngchul Yoo, Gynheung An: Crop Biotech Institute
  • Anke Reinders, John M. Ward: Kyung Hee University, Yongin 446–701, Korea; Department of Plant Biology, University of Minnesota, St.Paul, Minnesota 55108–1095
  • Pham Quoc Tuan, Sang-Bong Choi: Division of Bioscience and Bioinformatics, Myongji University, Yongin 449–728, Korea
  • Geul Bang, Youn-Il Park: Department of Biological Science and Analytical Science and Technology, Chungnam National University, Daejeon 305–764, Korea
  • W. Siao : J.-Y. Chen : H.-H. Hsiao : P. Chung : S.-J. Wang: Department of Agronomy, National Taiwan University, No. 1, Section 4, Roosevelt Rd.

References

  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 Siao W, Chen J Y, Hsiao H H, et al. Characterization of OsSUT2 expression and regulation in germinating embryos of rice seeds[J]. Rice, 2011, 4(2): 39-49.
  2. Kahsay R Y, Gao G, Liao L. An improved hidden Markov model for transmembrane protein detection and topology prediction and its applications to complete genomes[J]. Bioinformatics, 2005, 21(9): 1853-1858.
  3. 3.0 3.1 3.2 Eom J S, Cho J I, Reinders A, et al. Impaired function of the tonoplast-localized sucrose transporter in rice, OsSUT2, limits the transport of vacuolar reserve sucrose and affects plant growth[J]. Plant Physiology, 2011, 157(1): 109-119.
  4. Aoki N, Hirose T, Scofield G N, et al. The sucrose transporter gene family in rice[J]. Plant and Cell Physiology, 2003, 44(3): 223-232.