The National Key Facility for Crop Gene Resources and Genetic Improvement, NFCRI, MOA Key Laboratory of Soybean Biology Beijing, Institute of Crop Science, The Chinese Academy of Agricultural Sciences, 12 Zhongguancun South Street, Beijing 100081, PR China.
J Exp Bot. 2013 Apr;64(7):1917-26. doi: 10.1093/jxb/ert053. Epub 2013 Mar 25.
Soybean seeds provide an excellent source of protein for human and livestock nutrition. However, their nutritional quality is hampered by a low concentration of the essential sulfur amino acid, methionine (Met). In order to study factors that regulate Met synthesis in soybean seeds, this study used the Met-insensitive form of Arabidopsis cystathionine γ-synthase (AtD-CGS), which is the first committed enzyme of Met biosynthesis. This gene was expressed under the control of a seed-specific promoter, legumin B4, and used to transform the soybean cultivar Zigongdongdou (ZD). In three transgenic lines that exhibited the highest expression level of AtD-CGS, the level of soluble Met increased significantly in developing green seeds (3.8-7-fold). These seeds also showed high levels of other amino acids. This phenomenon was more prominent in two transgenic lines, ZD24 and ZD91. The total Met content, which including Met incorporated into proteins, significantly increased in the mature dry seeds of these two transgenic lines by 1.8- and 2.3-fold, respectively. This elevation was accompanied by a higher content of other protein-incorporated amino acids, which led to significantly higher total protein content in the seeds of these two lines. However, in a third transgenic line, ZD01, the level of total Met and the level of other amino acids did not increase significantly in the mature dry seeds. This line also showed no significant change in protein levels. This suggests a positive connection between high Met content and the synthesis of other amino acids that enable the synthesis of more seed proteins.
大豆种子为人类和牲畜的营养提供了极好的蛋白质来源。然而，其营养价值受到必需的硫氨基酸蛋氨酸（Met）浓度低的限制。为了研究调节大豆种子中 Met 合成的因素，本研究使用了拟南芥半胱氨酸γ-合酶（AtD-CGS）的 Met 不敏感形式，它是 Met 生物合成的第一个关键酶。该基因在种子特异性启动子 legumin B4 的控制下表达，并用于转化大豆品种 Zigongdongdou（ZD）。在三个表现出最高 AtD-CGS 表达水平的转基因系中，发育中的绿色种子中的可溶性 Met 水平显著增加（3.8-7 倍）。这些种子还表现出高水平的其他氨基酸。这种现象在两个转基因系 ZD24 和 ZD91 中更为明显。这两个转基因系的成熟干种子中总 Met 含量（包括掺入蛋白质的 Met）分别显著增加了 1.8 倍和 2.3 倍。这种升高伴随着其他掺入蛋白质的氨基酸含量的增加，导致这两个系的种子中总蛋白质含量显著增加。然而，在第三个转基因系 ZD01 中，成熟干种子中的总 Met 和其他氨基酸水平没有显著增加。该系的蛋白质水平也没有明显变化。这表明高 Met 含量与其他氨基酸的合成之间存在正相关关系，从而能够合成更多的种子蛋白质。
