同化产物由源向库, 尤其是向发育种子的转运, 是植物生长和种子产量的关键。前期我们用不同籽粒大小的大豆品种, 对发育种子进行了转录组分析，发现糖转运蛋白家族中GmST1和GmST5特异地在种子发育早期高丰度表达，暗示其在种子发育和产量形成中起关键作用。本研究拟对其功能及作用机制进行研究。将: 1)利用基因启动子融合GUS等载体，在转基因大豆中分析GmST1和GmST5基因的时空表达特征；2)通过酵母互补、荧光共振能量转移传感等方法确定其转运底物；3)解析GmST1和GmST5基因在大豆品种群体中的差异及其选择驯化效应。4)培育GmST1和GmST5基因超(原位)表达和敲除转基因大豆，分析GmST1和GmST5基因的不同单倍型、表达丰度，与种子糖分积累、种子发育和种子大小的关联，阐明其功能及作用机制。研究结果将鉴定参与大豆种子发育的重要糖转运体成员，为培育高产大豆品种提供新候选基因和新种质。

The transport of assimilate from the source (leaves) to the sink (roots, seeds and so on) tissues, especially to the developing seeds, is essential for the plant growth and seed yield. Previously, we carried out the transcriptome analyses in three early seed developmental stages using two genotypes with contrasting seed size. The study identified two novel sugar transporters, GmST1 and GmST5 that were highly and specifically expressed in early seed developmental stage，implying that they may play important roles in seed development and yield. This project aims to study the biological function and regulatory mechanism of GmST1 and GmST5. Scientific goals include, 1) to evaluate the expression profile of GmST1 and GmST5 by analyzing the expression of the reporters (GUS and YFP) in the transgenic soybean plants generated from the constructs of the endogenous promoters or whole length genomic sequence fusing to the reporter gene(s); 2) to identify the substrates of these sugar transporters using yeast complementation assay and the high-sensitivity fluorescence resonance energy transfer (FRET) sugar sensor assay; 3) to analyze the diversity and signatures of selection on GmST1 and GmST5 genes among wild soybean (Glycine Soja) cultivated and landrace soybean varieties; 4) to illustrate the association between the hapotypes of GmST1 and GmST5 genes, their expression levels and sugar contents in seeds, seed development, and the seed size using transgenic soybean plants that either overexpressed or knockout the GmST1 and GmST5 genes. Based on the results, the function of regulatory mechanism of the GmST1 and GmST5 genes will be explored. The project will define novel sugar transporters for soybean seed development and filling, which will provide a new venue for the engineering of soybean plants with enhanced transport of assimilates to developing seeds, therefore increase yield.