Expression and assembly of cholera toxin B subunit (CTB) in transgenic carrot (Daucus carota L.)

We expressed the cholera toxin B subunit (CTB) fused to an endoplasmic reticulum retention signal (SEKDEL) in carrot roots using an Agrobacterium-mediated transformation method. Fourteen independent transgenic lines were regenerated via somatic embryogenesis after 6 months of culture. The sCTB gene was detected in the genomic DNA of transgenic carrot by PCR amplification. Expressions and assembly of sCTB protein into oligomeric structures of pentameric size were observed in transgenic plant extracts by Western blot analysis. The sCTB produced by transgenic carrot roots demonstrated strong affinity for GM1-ganglioside, suggesting that the sCTB conserved the antigenic sites for binding and proper folding of the pentameric sCTB structure. The expression level of sCTB comprised approximately 0.48% of total soluble protein (TSP) in root of transgenic carrot.