Transgenic soybean plants overexpressing O-acetylserine sulfhydrylase accumulate enhanced levels of cysteine and Bowman–Birk protease inhibitor in seeds

• Published in: Planta Vol. 235; no. 1; pp. 13 - 23
• Main Authors: Kim, Won-Seok, Chronis, Demosthenis, Juergens, Matthew, Schroeder, Amy C, Hyun, Seung Won, Jez, Joseph M, Krishnan, Hari B
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer 01.01.2012; Springer-Verlag; Springer Nature B.V
• Subjects: Agriculture; amino acid composition; Amino Acid Sequence; Amino acids; animal growth; animal source protein; Base Sequence; Biological and medical sciences; Biomedical and Life Sciences; Bowman-Birk inhibitor; Cysteine; Cysteine - biosynthesis; cysteine proteinase inhibitors; Cysteine Synthase - biosynthesis; Cysteine Synthase - genetics; Cysteine Synthase - metabolism; Developmental stages; Ecology; enzyme activity; Enzymes; feeds; Forestry; Fundamental and applied biological sciences. Psychology; Gene Dosage; Gene Expression Regulation, Plant; gene overexpression; Genes, Plant; Genetic Engineering; Genetic Variation; Glycine max - chemistry; Glycine max - enzymology; Glycine max - genetics; Glycine max - metabolism; Leaves; Life Sciences; Methionine; Molecular Sequence Data; Original Article; Plant Sciences; Plants; Plants, Genetically Modified - enzymology; Plants, Genetically Modified - genetics; Plants, Genetically Modified - metabolism; Protease inhibitors; protein synthesis; Proteinase inhibitors; Proteins; seed development; Seeds; Seeds - chemistry; Seeds - enzymology; Seeds - genetics; Seeds - metabolism; soy protein; Soybean Proteins - biosynthesis; Soybean Proteins - genetics; Soybean Proteins - metabolism; Soybeans; sulfhydrylase; Sulfur; Transgenes; Transgenic plants; Trypsin Inhibitor, Bowman-Birk Soybean - metabolism; acetylserine sulfhydrylase; Nutritional quality; Cysteine; Soybean; Bowman–Birk protease inhibitor; Essential amino acid; Seeds; Enzyme; Nutritive value; Plant biology; Gene overexpression; Lyases; Glycine max; Bowman―Birk protease inhibitors; Grain legume; Leguminosae; Dicotyledones; Aminoacid; Cysteine synthase; Nutritional quality O-acetylserine sulfhydrylase; Angiospermae; Spermatophyta; Level; Transgenic plant; Carbon-oxygen lyases; Protease inhibitor
• ISSN: 1432-2048; 0032-0935; 1432-2048
• DOI: 10.1007/s00425-011-1487-8

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.