Effect of climate conditions and plant developmental stage on the stability of antibodies expressed in transgenic tobacco

Plants are regarded as a promising system for the production of heterologou s proteins. However, little is known about the influence of plant physiolog y and plant development on the yield and quality of the heterologous protei ns produced in plants. To investigate this, tobacco (Nicotiana tabacum cv S amsun NN) was transformed with a single construct that contained behind con stitutive promoters the light- and heavy-chain genes of a mouse antibody. T he in planta stability of the antibody was analyzed in transgenic plants th at were grown under high and low irradiation at 15 degrees C and 25 degrees C. High-light conditions favored the production of biomass, of total solub le protein, and of antibody. The plants grown at 25 degrees C developed fas ter and contained less antibody per amount of leaf tissue than the plants g rown at 15 degrees C. Both endogenous protein and antibody content showed a strong decline during leaf development. The heavy chains of the antibody u nderwent in planta degradation via relatively stable fragments. In vitro in cubations of purified plantibody with leaf extracts of wild-type tobacco in dicated the involvement of acidic proteases. It is interesting that the sam e antibody produced by mouse hybridoma cells exhibited higher stability in this in vitro assay. This may be explained by the assumption that the plant type of N-glycosylation contributes less to the stability of the antibody than the mouse-type of N-glycosylation. The results of this study indicate that proteolytic degradation during plant development can be an important f actor affecting yield and homogeneity of heterologous protein produced by t ransgenic plants.