Method for producing target proteins using amino acids and pyruvic acids in culture of plant cells

A method for producing a target protein is provided to secure an optimized culture condition for enhancing the production yield of the target protein by inducing the protein expression without exchange of a cell growth medium with a sugar-free medium and addition of pyruvic acid during the induction period of protein expression, thereby mass-producing a recombinant protein. A method for producing a target protein by culturing a transgenic plant cell including a promoter expressing the protein without sugars and a gene encoding the target protein comprises the steps of: (a) culturing the transgenic plant cell in a sugar-rich medium to grow the pant cells; and (b) culturing the transgenic plant cells with addition of an amino acid mixture to the culture of step(a) without exchange of a cell growth medium with a sugar-depleted medium, wherein the target protein is a human CTLA4Ig, the promoter is an RAmy3D promoter of alpha-amylase and the plant cell is a rice cell. Further, the culture is fed-batch culture.