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Expression of a synthetic E. coli heat-labile enterotoxin B sub-unit (LT-B) in maize
Molecular Breeding
  • Rachel Chikwamba, Iowa State University
  • Jennifer McMurray, Iowa State University
  • Huixia Shou, Iowa State University
  • Bronwyn Frame, Iowa State University
  • Sue Ellen Pegg, Iowa State University
  • Paul Scott, United States Department of Agriculture
  • Hugh Mason, Boyce Thompson Institute for Plant Research
  • Kan Wang, Iowa State University
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We have produced the B subunit of the enterotoxigenic Escherichia coli (ETEC) heat-labile enterotoxin (LT-B) in transgenic maize seed. LT-B is a model antigen that induces a strong immune response upon oral administration and enhances immune responses to conjugated and co-administered antigens. Using a synthetic LT-B gene with optimized codon sequence, we examined the role of promoters and the SEKDEL endoplasmic reticulum retention motif in LT-B accumulation in callus and in kernels. Two promoters, the constitutive CaMV 35S promoter and the maize 27 kDa gamma zein promoter, which directs endosperm-specific gene expression in maize kernels, regulated LT-B expression. Ganglioside-dependent ELISA analysis showed that using the constitutive promoter, maximum LT-B level detected in callus was 0.04% LT-B in total aqueous-extractable protein (TAEP) and 0.01% in R1 kernels of transgenic plants. Using the gamma zein promoter, LT-B accumulation reached 0.07% in R1 kernels. The SEKDEL resulted in increased LT-B levels when combined with the gamma zein promoter. We monitored LT-B levels under greenhouse and field conditions over three generations. Significant variability in gene expression was observed between transgenic events, and between plants within the same event. A maximum of 0.3% LT-B in TAEP was measured in R3 seed of a transgenic line carrying CaMV 35S promoter/LT-B construct. In R3 seed of a transgenic line carrying the gamma zein promoter/LT-B construct, up to 3.7% LT-B in TAEP could be detected. We concluded that maize seed can be used as a production system for functional antigens.

This article is published as Chikwamba, Rachel, Jennifer McMurray, Huixia Shou, Bronwyn Frame, Sue Ellen Pegg, Paul Scott, Hugh Mason, and Kan Wang. "Expression of a synthetic E. coli heat-labile enterotoxin B sub-unit (LT-B) in maize." Molecular breeding 10, no. 4 (2002): 253-265.

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Rachel Chikwamba, Jennifer McMurray, Huixia Shou, Bronwyn Frame, et al.. "Expression of a synthetic E. coli heat-labile enterotoxin B sub-unit (LT-B) in maize" Molecular Breeding Vol. 10 Iss. 4 (2002) p. 253 - 265
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