Recombinant Pharmaceuticals from Plants: The Plant Endomembrane System as Bioreactor

A domain of a maize storage protein can be used recombinantly to form ER-located protein bodies. Electron micrograph of a thin section of a young leaf of transgenic tobacco that expresses “zeolin,” a fusion between the N-terminal domain of the maize prolamin γ-zein and the vacuolar protein phaseolin. The recombinant protein forms electron-dense protein bodies (PB) not normally found in leaf cells. Zeolin was visualized with antibodies against phaseolin and secondary antibody-gold complex (black dots inside the PBs). The large empty area that occupies most of the cell is the lytic vacuole. [Ch, chloroplast; Mt, mitochondrion; CW, cell wall. Bar = 500 nm. Reproduced from (35).]