, Volume 235, Issue 1, pp 13–23 | Cite as

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. KrishnanEmail author
Original Article


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.


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



O-acetylserine sulfhydrylase


Serine acetyltransferase


Homoserine dehydrogenase



We thank the University of Missouri Plant Transformation Core Facility for the production of transgenic soybean lines. Work in the Jez lab was funded by a US Department of Agriculture grant (NRI-2005-02518) to J.M.J., M.J. and A.C.S. were also supported in part by American Society of Plant Biologists Summer Undergraduate Research Fellowships. Product names are necessary to report factually on available data; however, the University of Missouri and the USDA neither guarantee nor warrant the standard of product, and the use of the name by the University of Missouri and the USDA implies no approval of the product to the exclusion of others that may be suitable.

Supplementary material

425_2011_1487_MOESM1_ESM.doc (788 kb)
Supplementary material 1 (DOC 788 kb)
425_2011_1487_MOESM2_ESM.doc (42 kb)
Supplementary material 2 (DOC 41 kb)


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Copyright information

© Springer-Verlag (outside the USA) 2011

Authors and Affiliations

  • Won-Seok Kim
    • 1
  • Demosthenis Chronis
    • 1
  • Matthew Juergens
    • 2
  • Amy C. Schroeder
    • 2
  • Seung Won Hyun
    • 3
  • Joseph M. Jez
    • 2
  • Hari B. Krishnan
    • 1
    • 4
    Email author
  1. 1.Division of Plant SciencesUniversity of MissouriColumbiaUSA
  2. 2.Department of BiologyWashington UniversitySt. LouisUSA
  3. 3.Department of StatisticsNorth Dakota State UniversityFargoUSA
  4. 4.Plant Genetics Research Unit, United States Department of Agriculture/Agricultural Research Service, 108 Curtis HallUniversity of MissouriColumbiaUSA

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