Hossain Tahzeeba, Rosenberg Irwin, Selhub Jacob, Kishore Ganesh, Beachy Roger, Schubert Karel
Donald Danforth Plant Science Center, 975 North Warson Road, St. Louis, MO 63132, USA.
Proc Natl Acad Sci U S A. 2004 Apr 6;101(14):5158-63. doi: 10.1073/pnas.0401342101. Epub 2004 Mar 24.
Humans depend on plants as a major source of dietary folates. Inadequate dietary levels of the vitamin folate can lead to megaloblastic anemia, birth defects, impaired cognitive development, and increased risk of cardiovascular disease and cancer. The biofortification of folate levels in food crops is a target for metabolic engineering. Folates are synthesized de novo from pterins and para-amino benzoic acid, which are subsequently combined to form dihydropteroate, the direct precursor to dihydrofolate. We postulated that GTP cyclohydrolase-1, which catalyzes the first committed step in pterin biosynthesis, was a rate-limiting step in pterin synthesis in plants and, therefore, in folate synthesis. On this basis, we proposed that the expression of an unregulated bacterial GTP cyclohydrolase-1 in plants would increase pterin biosynthesis with a concomitant enhancement of folate levels. The folE gene encoding GTP cyclohydrolase-1 was cloned from Escherichia coli and introduced into Arabidopsis thaliana through plant transformation. The expression of bacterial GTP cyclohydrolase-1 in transgenic Arabidopsis resulted in a 1,250-fold and 2- to 4-fold enhancement of pterins and folates, respectively. These results helped to identify other potential factors regulating folate synthesis, suggesting ways to further enhance folate levels in food crops.
人类依赖植物作为膳食叶酸的主要来源。膳食中叶酸水平不足会导致巨幼细胞贫血、出生缺陷、认知发育受损以及心血管疾病和癌症风险增加。提高粮食作物中的叶酸水平是代谢工程的一个目标。叶酸由蝶呤和对氨基苯甲酸从头合成，随后二者结合形成二氢蝶酸，即二氢叶酸的直接前体。我们推测，催化蝶呤生物合成第一步的GTP环化水解酶-1是植物中蝶呤合成的限速步骤，因此也是叶酸合成的限速步骤。在此基础上，我们提出在植物中表达不受调控的细菌GTP环化水解酶-1将增加蝶呤生物合成，并随之提高叶酸水平。编码GTP环化水解酶-1的folE基因从大肠杆菌中克隆出来，并通过植物转化导入拟南芥。细菌GTP环化水解酶-1在转基因拟南芥中的表达分别使蝶呤和叶酸提高了1250倍以及2至4倍。这些结果有助于确定调控叶酸合成的其他潜在因素，为进一步提高粮食作物中的叶酸水平提供了思路。
