Müntz K, Christov V, Saalbach G, Saalbach I, Waddell D, Pickardt T, Schieder O, Wüstenhagen T
Institut für Pflanzengenetik und Kulturpflanzenforschung, Gatersleben, Germany.
Nahrung. 1998 Aug;42(3-4):125-7. doi: 10.1002/(sici)1521-3803(199808)42:03/04<125::aid-food125>3.3.co;2-1.
Methionine (Met) is the primary limiting essential amino acid in grain legumes. The imbalance in amino acid composition restricts their biological value (BV) to 55 to 75% of that of animal protein. So far improvement of the BV could not be achieved by conventional breeding. Therefore, genetic engineering was employed by several laboratories to resolve the problem. Three strategies have been followed. A) Engineering for increased free Met levels; B) engineering of endogenous storage proteins with increased numbers of Met residues; C) transfer of foreign genes encoding Met-rich proteins, e.g. the Brazil nut 2S albumin (BNA) and its homologue from sunflower, into grain legumes. The latter strategy turned out to be most promising. In all cases the gene was put under the control of a developmentally regulated seed specific promoter and transferred into grain legumes using the bacterial Agrobacterium tumefaciens-system. Integration into and copy numbers in the plant genome as well as Mendelian inheritance and gene dosage effects were verified. After correct precursor processing the mature 2S albumin was intracellularly deposited in protein bodies which are part of the vacuolar compartment. The foreign protein amounted to 5 to 10% of the total seed protein in the best transgenic lines of narbon bean (Vicia narbonensis L., used in the authors' laboratories), lupins (Lupinus angustifolius L., used in CSIRO, Australia), and soybean (Glycine max (L.) Merr., used by Pioneer Hi-Bred, Inc., USA). In the narbon bean the increase of Met was directly related to the amount of 2S albumin in the transgenic seeds, but in soybean it remained below the theoretically expected value. Nevertheless, trangenic soybean reached 100%, whereas narbon bean and lupins reached approximately 80% of the FAO-standard for nutritionally balanced food proteins. These results document that the Met problem of grain legumes can be resolved by genetic engineering.
蛋氨酸（Met）是豆科作物中主要的限制性必需氨基酸。氨基酸组成的不平衡将它们的生物学价值（BV）限制在动物蛋白的55%至75%。到目前为止，通过传统育种无法实现BV的提高。因此，几个实验室采用基因工程来解决这个问题。遵循了三种策略。A） 工程改造以提高游离Met水平；B） 对具有更多Met残基的内源性储存蛋白进行工程改造；C） 将编码富含Met蛋白的外源基因，如巴西坚果2S白蛋白（BNA）及其来自向日葵的同源物，转入豆科作物。事实证明，后一种策略最有前景。在所有情况下，该基因都置于发育调控的种子特异性启动子的控制下，并使用根癌土壤杆菌系统转入豆科作物。验证了其在植物基因组中的整合、拷贝数以及孟德尔遗传和基因剂量效应。经过正确的前体加工后，成熟的2S白蛋白在细胞内沉积在作为液泡区室一部分的蛋白体中。在作者实验室使用的窄叶羽扇豆（Vicia narbonensis L.）、澳大利亚联邦科学与工业研究组织（CSIRO）使用的窄叶羽扇豆（Lupinus angustifolius L.）以及美国先锋良种公司（Pioneer Hi-Bred, Inc.）使用的大豆（Glycine max (L.) Merr.）的最佳转基因品系中，外源蛋白占种子总蛋白的5%至10%。在窄叶羽扇豆中，Met的增加与转基因种子中2S白蛋白的量直接相关，但在大豆中仍低于理论预期值。尽管如此，转基因大豆达到了100%，而窄叶羽扇豆和羽扇豆达到了营养均衡食品蛋白质的粮农组织标准的约80%。这些结果证明，豆科作物的Met问题可以通过基因工程解决。
