Folates are a group of water-soluble B vitamins that are essential for all organisms. Although plants and microbes can synthesize them, humans cannot, and insufficient intake of folates can lead to several disorders. It is therefore important to find folate sources that can help alleviate folate malnutrition. Cereals are poor sources of folates but contain high levels of MeFox, a pyrazino-s-triazine derivative of 4α-hydroxy-5-methyltetrahydrofolate that is a biologically inactive, oxidized form of folate, suggesting potential for targeting its formation. Now, Liang et al. have enhanced the metabolic flux by co-overexpression of two folate biosynthesis genes and blocked folate oxidation via gene editing to create folate-biofortified rice.

The team identified and validated OsGFT as having a crucial role in MeFox formation in rice. Its targeted knockout by CRISPR–Cas9 editing resulted in rice plants with elevated levels of 5-methyltetrahydrofolate as well as other biologically active folates. Next, the team combined their gene editing strategy with the overexpression of Arabidopsis genes GTP cyclohydrolase 1 (GCH1) and aminodeoxychorismate synthase (ADCS), responsible for the first steps in the biosynthesis of key components of the folate scaffold. This led to transgenic plants containing total folate levels up to 13-fold higher than the wild type (WT), and the MeFox average content was 33% of that of the WT. Furthermore, no plant nor seed showed phenotypic differences from the WT, and the team demonstrated that the increased levels of folates were also found in milled rice. This study showcased the potential for engineered whole grain rice to address deficiencies in folate nutrition.

叶酸是一组水溶性 B 族维生素，对所有生物体都是必需的。虽然植物和微生物可以合成它们，但人类不能，叶酸摄入不足会导致多种疾病。因此，找到有助于缓解叶酸营养不良的叶酸来源非常重要。谷物是叶酸的不良来源，但含有高水平的 MeFox，MeFox 是 4α-羟基-5-甲基四氢叶酸的吡嗪-s-三嗪衍生物，是叶酸的一种生物无活性的氧化形式，表明有可能靶向其形成。现在，Liang 等人通过共过表达两个叶酸生物合成基因来增强代谢通量，并通过基因编辑阻断叶酸氧化以产生叶酸生物强化水稻。

该团队确定并验证了 OsGFT 在水稻 MeFox 形成中起着至关重要的作用。它通过 CRISPR-Cas9 编辑靶向敲除导致水稻植株的 5-甲基四氢叶酸以及其他生物活性叶酸水平升高。接下来，该团队将他们的基因编辑策略与拟南芥基因 GTP 环水解酶 1 （GCH1） 和氨基脱氧胆酸合酶 （ADCS） 的过表达相结合，负责叶酸支架关键成分生物合成的第一步。这导致转基因植物的总叶酸含量比野生型 （WT） 高 13 倍，MeFox 平均含量为 WT 的 33%。此外，没有植物或种子显示出与 WT 的表型差异，并且该团队证明在碾米中也发现了叶酸水平的增加。这项研究展示了工程全麦米解决叶酸营养缺乏症的潜力。