Isolation and Characterization of the Soybean Sg-3 Gene that is Involved in Genetic Variation in Sugar Chain Composition at the C-3 Position in Soyasaponins
Isolation and Characterization of the Soybean Sg-3 Gene that is Involved in Genetic Variation in Sugar Chain Composition at the C-3 Position in Soyasaponins
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DOI：
10.1093/pcp/pcy019
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发表时间：
2018-04-01
影响因子：
4.9
通讯作者：
Ishimoto, Masao
中科院分区：
文献类型：
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作者：
Yano, Ryoichi;Takagi, Kyoko;Ishimoto, Masao
大豆皂苷是大豆种子中存在的特殊代谢物，影响大豆食品的味道和质量。大豆皂苷的糖苷配基部分所连接的糖链的组成受遗传基因座如sg-1、sg-3和sg-4的调节。在这里，我们报告的Sg-3基因，这是负责共轭的末端（第三）葡萄糖（Glc）在C-3糖链的大豆皂甙的克隆和表征。Glyma基因10 G104700在sg-3栽培品种“Mikuriya-ao”中失活，这是由于基因组DNA的缺失导致C-3糖链上缺少末端Glc残基。Sg-3编码一个推定的糖基转移酶（UGT 91 H9），其预测的蛋白质序列与GmSGT 3的产物（Glyma. 08 G181000; UGT 91 H4），其在体外将鼠李糖（Rha）缀合至C-3糖链的第三位。重组Glyma。10 G104700蛋白可以利用UDP-Glc作为底物，将第三个Glc连接到C-3糖链上，并引入功能性Glyma。10 G104700转基因进入突变体补充了sg-3表型。相反，诱导Glyma中的提前终止密码子突变。10 G104700（W270*）导致sg-3表型，表明Glyma. 10 G104700是Sg-3。gmsgt 3（R339 H）突变体不能积累C-3糖链上第三个Rha的大豆皂苷，而sg-3 gmsgt 3双突变体的第三个Glc和Rha结合都被禁用。这些结果表明，Sg-3和GmSGT 3分别非冗余地参与大豆皂苷C-3糖链上第三个Glc和Rha的缀合。
Soyasaponins are specialized metabolites present in soybean seeds that affect the taste and quality of soy-based foods. The composition of the sugar chains attached to the aglycone moiety of soyasaponins is regulated by genetic loci such as sg-1, sg-3 and sg-4. Here, we report the cloning and characterization of the Sg-3 gene, which is responsible for conjugating the terminal (third) glucose (Glc) at the C-3 sugar chain of soyasaponins. The gene Glyma. 10G104700 is disabled in the sg-3 cultivar, 'Mikuriya-ao', due to the deletion of genomic DNA that results in the absence of a terminal Glc residue on the C-3 sugar chain. Sg-3 encodes a putative glycosyltransferase (UGT91H9), and its predicted protein sequence has a high homology with that of the product of GmSGT3 (Glyma. 08G181000; UGT91H4), which conjugates rhamnose (Rha) to the third position of the C-3 sugar chain in vitro. A recombinant Glyma. 10G104700 protein could utilize UDP-Glc as a substrate to conjugate the third Glc to the C-3 sugar chain, and introducing a functional Glyma. 10G104700 transgene into the mutant complemented the sg-3 phenotype. Conversely, induction of a premature stop codon mutation in Glyma. 10G104700 (W270*) resulted in the sg-3 phenotype, suggesting that Glyma. 10G104700 was Sg-3. The gmsgt3 (R339H) mutant failed to accumulate soyasaponins with the third Rha at the C-3 sugar chain, and the third Glc and Rha conjugations were both disabled in the sg-3 gmsgt3 double mutant. These results demonstrated that Sg-3 and GmSGT3 are non-redundantly involved in conjugation of the third Glc and Rha at the C-3 sugar chain of soyasaponins, respectively.