Browsing by Subject "Sucrose transporter"

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    AtSUC1 ROOT EXPRESSION AND SUCROSE RESPONSE LEADING TO ANTHOCYANIN ACCUMULATION
    (2019-12) Lasin, Praphapan
    Previous research indicated that AtSUC1 root expression is controlled by intragenic sequences. The 5’ upstream region (promoter) of AtSUC1 directs pollen and trichome expression, but not root expression. However, the whole AtSUC1 gene can drive root expression and sucrose-induced root expression. Here I show that root expression of AtSUC1 is controlled by the interaction between the promoter and its two short introns. Deletion of either intron from whole-gene-GUS constructs resulted in no root expression, showing that both introns are required. The two introns in tandem, fused to GUS, produce high constitutive expression throughout the vegetative parts of the plant. When combined with the promoter, the expression driven by the introns is reduced and localized to the roots. AtSUC1 expression is also induced by exogenous sucrose, and AtSUC1 is also required for sucrose-induced anthocyanins (Sivitz et al., 2008). Anthocyanin accumulation due to high sucrose was lesser in the AtSUC1 mutant compared to Col-0 wild type. A whole-gene-GUS construct expressing a non-functional AtSUC1 (D152N) mutant, that is transport inactive, was defective in sucrose-induced AtSUC1 expression and anthocyanins accumulation when expressed in an atsuc1-null background. The results indicated that sucrose uptake via AtSUC1 is required for sucrose-induced AtSUC1 expression and anthocyanin accumulation, and that the site for sucrose detection is intracellular.
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    Structure-function relationship of plant sucrose transporters (SUTs)
    (2012-07) Sun, Ye
    Sucrose transporters (SUTs or SUCs) are membrane proteins that transport sucrose and H+ into the cytoplam at a ratio of 1:1. They are important for the long-distance transport of sucrose in plants. However, little is known about the structure-function relationship of SUTs. In this thesis, the transport activity and substrate specificity of rice SUTs were measured using [14C] sucrose yeast uptake and oocyte electrophysiology. More importantly, a 3D structural model of rice sucrose transporter OsSUT1 was built using known crystal structures of transporters from E.coli as templates. Based on the predicted model, six charged amino acids in transmembrane spans were selected for mutagenesis, five of which turned out to be essential for the SUT transport function. One mutant, R188K, caused a complete loss of sucrose transport activity, and showed a H+ leak that could be blocked by sucrose. Based on electrophysiology experiments results, a putative binding interaction between Arg188 of OsSUT1 and hydroxyl groups of sucrose was proposed. A role of Arg188 in the substrate transport process was also suggested. In addition, methods to identify amino acids important for SUT substrate specificity were explored.