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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Folate biofortification in tomatoes by engineering the pteridine branch of folate synthesis
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Folate biofortification in tomatoes by engineering the pteridine branch of folate synthesis

机译：通过工程化叶酸合成的蝶啶分支来提高番茄中的叶酸生物强化能力

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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.
机译：植物是人类叶酸饮食的主要来源，但是许多水果，块茎和种子都缺乏这种维生素，叶酸缺乏是一个世界性的问题。植物从蝶啶，对氨基苯甲酸酯（PABA）和谷氨酸部分合成叶酸。已知在成熟的番茄果实中，蝶啶的合成能力会下降。因此，我们通过水果特异性的GTP环水解酶1（蝶啶合成的第一种酶）来应对这种下降。我们使用了基于哺乳动物GTP环水解酶1的合成基因，因为预计该酶会逃避植物中的反馈控制。相对于仅使用载体的对照，该工程操作将12个独立转化子中的水果蝶啶含量提高了3至140倍，将叶酸含量平均提高了2倍。叶酸的增加大部分是由5-甲基四氢叶酸聚谷氨酸盐和5,10-亚甲基四氢叶酸聚谷氨酸盐引起的，它们也是对照果实中叶酸的主要形式。积累的蝶啶包括新蝶呤，莫纳汀和羟甲基蝶呤。它们的还原形式，是叶酸生物合成中间体；和以前在植物中未发现的蝶啶苷。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库中的叶酸含量高的工程水果严重枯竭，通过果梗向此类水果提供PABA可使叶酸含量增加多达10倍。这些结果表明，适度增加蝶啶的产量可以显着提高食用植物中的叶酸含量，而增加PABA的供应量则可以进一步提高产量。

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