title: Transgenic soybean plants overexpressing O-acetylserine sulfhydrylase accumulate enhanced levels of cysteine and Bowman-Birk protease inhibitor in seeds.
abstract: Soybeans provide an excellent source of protein in animal feed. Soybean protein quality can be enhanced by increasing the concentration of sulfur-containing amino acids. Previous attempts to increase the concentration of sulfur-containing amino acids through the expression of heterologous proteins have met with limited success. Here, we report a successful strategy to increase the cysteine content of soybean seed through the overexpression of a key sulfur assimilatory enzyme. We have generated several transgenic soybean plants that overexpress a cytosolic isoform of O-acetylserine sulfhydrylase (OASS). These transgenic soybean plants exhibit a four- to tenfold increase in OASS activity when compared with non-transformed wild-type. The OASS activity in the transgenic soybeans was significantly higher at all the stages of seed development. Unlike the non-transformed soybean plants, there was no marked decrease in the OASS activity even at later stages of seed development. Overexpression of cytosolic OASS resulted in a 58-74% increase in protein-bound cysteine levels compared with non-transformed wild-type soybean seeds. A 22-32% increase in the free cysteine levels was also observed in transgenic soybeans overexpressing OASS. Furthermore, these transgenic soybean plants showed a marked increase in the accumulation of Bowman-Birk protease inhibitor, a cysteine-rich protein. The overall increase in soybean total cysteine content (both free and protein-bound) satisfies the recommended levels required for the optimal growth of monogastric animals.
authors.affiliation: Division of Plant Sciences, University of Missouri, Columbia, MO, 65211, USA.
authors.forename: Won-Seok
authors.initials: WS
authors.lastname: Kim
authors.forename: Demosthenis
authors.initials: D
authors.lastname: Chronis
authors.forename: Matthew
authors.initials: M
authors.lastname: Juergens
authors.forename: Amy C
authors.initials: AC
authors.lastname: Schroeder
authors.forename: Seung Won
authors.initials: SW
authors.lastname: Hyun
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Jez
authors.forename: Hari B
authors.initials: HB
authors.lastname: Krishnan
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003545:Cysteine / Q000096:biosynthesis*; D003547:Cysteine Synthase / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D018628:Gene Dosage; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005818:Genetic Engineering; D014644:Genetic Variation; D008969:Molecular Sequence Data; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000737:chemistry / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D030262:Soybean Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D013025:Glycine max / Q000737:chemistry / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D014358:Trypsin Inhibitor, Bowman-Birk Soybean / Q000378:metabolism*
chemical_list: D030262:Soybean Proteins; D014358:Trypsin Inhibitor, Bowman-Birk Soybean; D003547:Cysteine Synthase; D003545:Cysteine