Folate biofortification in tomatoes by engineering the pteridine branch of folate synthesis
Folate biofortification in tomatoes by engineering the pteridine branch of folate synthesis
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DOI：
10.1073/pnas.0404208101
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发表时间：
2004-09-21
影响因子：
11.1
通讯作者：
Hanson, AD
中科院分区：
文献类型：
--
作者：
de la Garza, RD;Quinlivan, EP;Hanson, AD
植物是人类饮食中叶酸的主要来源，但许多水果，块茎和种子缺乏这种维生素，叶酸缺乏症是一个世界性的问题。植物从蝶啶、对氨基苯甲酸盐（PABA）和谷氨酸盐部分合成叶酸。蝶啶合成能力下降，成熟的番茄果实，因此，我们反击了这种下降的果实特异性过表达的GTP环化水解酶1，蝶啶合成的第一个酶。我们使用基于哺乳动物GTP环化水解酶1的合成基因，因为该酶被预测在植物中逃避反馈控制。相对于单独的载体对照，这种工程操作在12个独立的转化体中使果实蝶啶含量提高了3至140倍，果实叶酸含量平均提高了2倍。大部分的叶酸增加是由5-甲基四氢叶酸多聚谷氨酸盐和5，10-亚甲基四氢叶酸多聚谷氨酸盐，这也是主要形式的叶酸在对照水果。积累的蝶啶包括新蝶呤、单蝶呤和羟甲基蝶呤;它们的还原形式，这是叶酸生物合成的中间体;以及以前在植物中未发现的蝶啶糖苷。具有中等水平的蝶啶过量生产的工程水果达到最高的叶酸水平。PABA池严重耗尽的工程水果，叶酸含量高，并提供这样的水果与PABA的果柄增加了叶酸含量高达10倍。这些结果表明，适度增加蝶啶产量可以显着提高食品植物中的叶酸含量，增加PABA的供应可以产生进一步的收益。
Plants are the main source of folate inhuman diets, but many fruits, tubers, and seeds are poor in this vitamin, and folate deficiency is a worldwide problem. Plants synthesize folate from pteridine, p-aminobenzoate (PABA), and glutamate moieties. Pteridine synthesis capacity is known to drop in ripening tomato fruit; therefore, we countered this decline by fruit-specific overexpression of GTP cyclohydrolase 1, the first enzyme of pteridine synthesis. We used a synthetic gene based on mammalian GTP cyclohydrolase 1, because this enzyme is predicted to escape feedback control in planta. This engineering maneuver raised fruit pteridine content by 3- to 140-fold and fruit folate content by an average of 2-fold among 12 independent transformants, relative to vector-alone controls. Most of the folate increase was contributed by 5-methyltetrahydrofolate polyglutamates and 5,10-methenyltetrahydrofolate polyglutamates, which were also major forms of folate in control fruit. The accumulated pteridines included neopterin, monapterin, and hydroxymethylpterin; their reduced forms, which are folate biosynthesis intermediates; and pteridine glycosides not previously found in plants. Engineered fruit with intermediate levels of pteridine overproduction attained the highest folate levels. PABA pools were severely depleted in engineered fruit that were high in folate, and supplying such fruit with PABA by means of the fruit stalk increased their folate content by up to 10-fold. These results demonstrate that engineering a moderate increase in pteridine production can significantly enhance the folate content in food plants and that boosting the PABA supply can produce further gains.