Production of peptides and proteins by accumulation in plant endoplasmic reticulum-derived protein bodies

A method for producing calcitonin in a plant host system, comprising:

• a) transforming a plant host system with an expression vector or with a nucleic acid construct comprising a regulatory sequence for the transcription of a nucleic acid molecule that comprises:
• (i) a first nucleic acid sequence comprising a nucleotide sequence that encodes γ-zein protein, or a fragment thereof capable of directing and retaining a protein towards the endoplasmic reticulum (ER) of a plant cell,
• (ii) a second nucleic acid sequence containing a nucleotide sequence that encodes an amino acid sequence that is specifically cleavable by enzymatic or chemical means, and
• (iii) a third nucleic acid sequence containing the nucleotide sequence that encodes calcitonin,
• wherein the 3′ end of said first nucleic acid sequence is linked to the 5′ end of said second nucleic acid sequence and the 3′ end of said second nucleic acid sequence is linked to the 5′ end of said third nucleic acid sequence;
• b) generating complete plants from said plant host systems transformed with said expression vector or nucleic acid construct;
• c) growing such transformed plants under conditions that allow the production and expression of calcitonin in the form of a fusion protein;
• and optionally
• d) isolating, purifying said fusion protein and treating said fusion protein in order to release calcitonin.