Dual targeting of xylanase to chloroplasts and peroxisomes as a means to increase protein accumulation in plant cells.

One of the limiting factors in the production of recombinant proteins in transgenic plants is the low level of protein accumulation. A strategy was investigated for a high level of protein accumulation in plant cells. A fungal xylanase encoded by XYLII of Trichoderma reesei was chosen as the model protein because xylanases have a high potential for applications in environment-related technologies. Xylanase was expressed in the cytosol or targeted either to chloroplasts or peroxisomes alone, or to both organelles simultaneously. When xylanase was targeted to both chloroplasts and peroxisomes simultaneously the amount of xylanase accumulated was 160% of that in chloroplasts alone and 240% of that in peroxisomes alone although the transcript levels were similar among these constructs. The growth stage of the transgenic plants also affected the total amount of xylanase; the highest level of accumulation occurred at the time of flowering. This study provides genetic and biochemical data demonstrating that a high level of protein accumulation in transgenic plants can be obtained by targeting a protein to both chloroplasts and peroxisomes at the same time.