Characterization of OsSUT2 Expression and Regulation in Germinating Embryos of Rice Seeds

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. 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. Exogenous sucrose was sensed by a sensor localized on the plasma membrane and functioned as an enhancer to promote OsSUT2 expression. Based on OsSUT2 promoter::GUS expression in germinating seeds of transgenic rice, OsSUT2 was significantly 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.