A TROUT GROWTH-HORMONE IS EXPRESSED, CORRECTLY FOLDED AND PARTIALLY GLYCOSYLATED IN THE LEAVES BUT NOT THE SEEDS OF TRANSGENIC PLANTS

The growth hormone gene of the rainbow trout (tGH-II) was expressed in leaves of transgenic tobacco plants and seeds of transgenic Arabidopsis plants using tissue-specific promoters. Although in the leaves and the seeds comparable amounts of tGH-II mRNA could be detected, the protein could only be identified in the tobacco leaves. Passage of the hormone into the secretory pathway, mediated by the signal sequence of the extracellular tobacco PR1-b (pathogenesis-related) protein, resulted in correct disulphide bridge formation and (partial) glycosylation of the hormone. In contrast, cytoplasmic expression resulted in misfolding and partial breakdown of the protein. The data demonstrate that synthesis, folding and glycosylation of heterologous proteins in plants is dependent both on subcellular location as well as on the tissue or cell type in which the protein is expressed.