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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 of tomato fruit
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Folate biofortification of tomato fruit

机译：番茄果实的叶酸生物强化

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Folate deficiency leads to neural tube defects and other human diseases, and is a global health problem. Because plants are major folate sources for humans, we have sought to enhance plant folate levels (biofortification). Folates are synthesized from pteridine, p-aminobenzoate (PABA), and glutamate precursors. Previously, we increased pteridine production in tomato fruit up to 140-fold by overexpressing GTP cyclohydrolase Ⅰ, the first enzyme of pteridine synthesis. This strategy increased folate levels 2-fold, but engineered fruit were PABA-depleted. We report here the engineering of fruit-specific overexpression of aminodeoxychorismate syn-thase, which catalyzes the first step of PABA synthesis. The resulting fruit contained an average of 19-fold more PABA than controls. When transgenic PABA- and pteridine-overproduction traits were combined by crossing, vine-ripened fruit accumulated up to 25-fold more folate than controls. Folate accumulation was almost as high (up to 15-fold) in fruit harvested green and ripened by ethylene-gassing, as occurs in commerce. The accumulated folates showed normal proportions of one-carbon forms, with 5-methyltetrahy-drofolate the most abundant, but were less extensively polyglu-tamylated than controls. Folate concentrations in developing fruit did not change in controls, but increased continuously throughout ripening in transgenic fruit. Pteridine and PABA levels in transgenic fruit were > 20-fold higher than in controls, but the pathway intermediates dihydropteroate and dihydrofolate did not accumulate, pointing to a flux constraint at the dihydropteroate synthesis step. The folate levels we achieved provide the complete adult daily requirement in less than one standard serving.
机译：叶酸缺乏会导致神经管缺陷和其他人类疾病，是全球性的健康问题。由于植物是人类的主要叶酸来源，因此我们寻求提高植物叶酸水平（生物强化）。叶酸由蝶啶，对氨基苯甲酸酯（PABA）和谷氨酸盐前体合成。以前，我们通过过度表达蝶啶合成的第一种酶GTP环水解酶Ⅰ，将番茄果实中的蝶啶产量提高了140倍。这种策略将叶酸水平提高了2倍，但工程水果被PABA消耗掉了。我们在这里报告了氨基脱氧胆酸合酶的水果特异性过表达的工程学，该酶催化了PABA合成的第一步。所得果实的PABA平均比对照组高19倍。当通过杂交将转基因的PABA和蝶啶的过量生产性状结合在一起时，葡萄藤果实积累的叶酸比对照多25倍。绿色水果收获的果实中的叶酸积累几乎与商业中一样高（高达15倍），并且通过放气乙烯成熟。累积的叶酸显示正常比例的一碳形式，其中5-甲基四氢-叶酸最丰富，但与对照相比，聚谷氨酰胺化程度较低。发育中的果实中的叶酸浓度在对照中没有变化，但是在转基因果实的整个成熟过程中却不断增加。转基因水果中的蝶啶和PABA水平比对照高20倍以上，但途径中间体二氢蝶呤和二氢叶酸并未积累，表明在二氢蝶呤合成步骤中存在通量约束。我们达到的叶酸水平以少于一标准的量就可以提供成年人的完整日常需求。

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