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

Won Seok Kim, Demosthenis Chronis, Matthew Juergens, Amy C. Schroeder, Seung Won Hyun, Joseph M. Jez, Hari B. Krishnan

Research output: Contribution to journalArticle

34 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)13-23
Number of pages11
Issue number1
Publication statusPublished - Jan 1 2012



  • Bowman-Birk protease inhibitor
  • Cysteine
  • Essential amino acid
  • Nutritional quality
  • O-acetylserine sulfhydrylase
  • Soybean

ASJC Scopus subject areas

  • Genetics
  • Plant Science

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