title: Co-expression of bacterial aspartate kinase and adenylylsulfate reductase genes substantially increases sulfur amino acid levels in transgenic alfalfa (Medicago sativa L.).
abstract: Alfalfa (Medicago sativa L.) is one of the most important forage crops used to feed livestock, such as cattle and sheep, and the sulfur amino acid (SAA) content of alfalfa is used as an index of its nutritional value. Aspartate kinase (AK) catalyzes the phosphorylation of aspartate to Asp-phosphate, the first step in the aspartate family biosynthesis pathway, and adenylylsulfate reductase (APR) catalyzes the conversion of activated sulfate to sulfite, providing reduced sulfur for the synthesis of cysteine, methionine, and other essential metabolites and secondary compounds. To reduce the feedback inhibition of other metabolites, we cloned bacterial AK and APR genes, modified AK, and introduced them into alfalfa. Compared to the wild-type alfalfa, the content of cysteine increased by 30% and that of methionine increased substantially by 60%. In addition, a substantial increase in the abundance of essential amino acids (EAAs), such as aspartate and lysine, was found. The results also indicated a close connection between amino acid metabolism and the tricarboxylic acid (TCA) cycle. The total amino acid content and the forage biomass tested showed no significant changes in the transgenic plants. This approach provides a new method for increasing SAAs and allows for the development of new genetically modified crops with enhanced nutritional value.
authors: State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing, China.
authors: Zongyong
authors: Z
authors: Tong
authors: State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing, China.
authors: Can
authors: C
authors: Xie
authors: State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing, China.
authors: Lei
authors: L
authors: Ma
authors: State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing, China.
authors: Liping
authors: L
authors: Liu
authors: State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing, China.
authors: Yongsheng
authors: Y
authors: Jin
authors: State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing, China.
authors: Jiangli
authors: J
authors: Dong
authors: State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing, China.
authors: Tao
authors: T
authors: Wang
mesh_terms: D000603:Amino Acids, Sulfur / Q000378:metabolism*; D001222:Aspartate Kinase / Q000235:genetics* / Q000378:metabolism; D018533:Biomass; D015139:Blotting, Southern; D015153:Blotting, Western; D002952:Citric Acid Cycle; D003433:Crosses, Genetic; D048168:Escherichia coli K12 / Q000201:enzymology* / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D005798:Genes, Bacterial / Q000235:genetics*; D000455:Medicago sativa / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D053858:Metabolic Networks and Pathways; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000235:genetics* / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D030821:Plants, Genetically Modified; D016133:Polymerase Chain Reaction; D011550:Pseudomonas aeruginosa / Q000201:enzymology* / Q000235:genetics; D015203:Reproducibility of Results; D012694:Serine / Q000031:analogs & derivatives / Q000378:metabolism; D014170:Transformation, Genetic
chemical_list: D000603:Amino Acids, Sulfur; D010940:Plant Proteins; D012694:Serine; D050862:Oxidoreductases Acting on Sulfur Group Donors; C019618:adenylylsulfate reductase; D001222:Aspartate Kinase; C043943:O-acetylserine