Engineering of Plant One-carbon Metabolism for Folate and Methionine Accumulation

本项目旨在通过控制四氢叶酸结合的一碳（C1）单元在质体中的网络，开发富含叶酸和可溶性蛋氨酸的植物代谢工程策略。植物将被改造成在质体中同时表达蛋氨酸合成酶和5,10-亚甲基四氢叶酸酶。两种过表达的方法将被测试：叶绿体靶向表达来自强组成核基因启动子，以及来自整合到质体基因组的基因的异位表达。代谢工程将在烟草（Nicotiana tabacum）中进行，这是一种可以常规获得质体转化的物种。丝氨酸羟甲基转移酶（SHMT）的同工酶也将被研究，因为这种酶可能是叶酸生物合成的限速步骤。了解SHMT的生化特性和亚细胞定位对于计划和解释拟议的代谢工程实验至关重要，这项研究将在拟南芥中进行，拟南芥是植物生物学中的模式物种，其中基因组资源是可用的。这项研究可以培育出富含叶酸和蛋氨酸的植物。叶酸缺乏与贫血、出生缺陷和血管疾病有关。增加叶酸含量的工程植物将代表天然叶酸的膳食来源，并可能潜在地解决人类叶酸摄取不足和相关健康疾病的问题。蛋氨酸是人类和非反刍动物必需的氨基酸。用于动物饲料的作物没有最佳的蛋氨酸含量，因此必须添加蛋氨酸。这种补充的高成本引起了最近对增加蛋氨酸含量的植物代谢工程的兴趣。该研究项目与罗格斯大学（Rutgers University）的Pal Maliga博士合作，将在代谢工程的各个方面培养学生和博士后。

The aim of this project is to develop strategies for metabolic engineering of plants enriched in folates and soluble methionine by manipulating the network of tetrahydrofolate-bound one-carbon (C1) units in plastids. Plants will be engineered to consist of simultaneous expression of methionine synthase and 5,10-methylenetetrahydrofolate enzymes in plastids. Two methods for over-expression will be tested: chloroplast-targeted expression from strong constitutive nuclear gene promoters, and ectopic expression from the genes incorporated into the plastid genome. Metabolic engineering will be carried out in tobacco (Nicotiana tabacum), a species in which plastid transformation can be routinely obtained. Isozymes of serine hydroxymethyltransferase (SHMT) will also be studied, as this enzyme may be a rate-limiting step of folate biosynthesis. Understanding the biochemical properties and subcellular localization of SHMT is essential for planning and interpretation of the proposed metabolic engineering experiments, a study that will be carried out in Arabidopsis thaliana, a model species in plant biology, in which genomic resources are available. The research can lead to the generation of plants enriched in folates and methionine. Folate deficiency in humans has been linked to anemia, birth defects and vascular diseases. Engineered plants with increased folate content will represent a dietary source of natural folates, and could potentially solve the problem of poor folate uptake, and the associated health disorders, for human populations. Methionine is an essential amino acid for humans and nonruminant animals. Crops used for animal feed do not have optimal methionine content, so they must be fortified with supplemental methionine. The high cost of this supplementation has prompted recent interest in metabolic engineering of plants with increased methionine content. The research program, in collaboration with Dr. Pal Maliga at Rutgers University, will train students and post-doctorals in all aspects of metabolic engineering.