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 Arabidops is plants using tissue-specific promoters. Although in the leaves and the seeds comparable amounts of tGH-II mRNA could be detected, the pro tein could only be identified in the tobacco leaves. Passage of the ho rmone into the secretory pathway, mediated by the signal sequence of t he extracellular tobacco PR1-b (pathogenesis-related) protein, resulte d in correct disulphide bridge formation and (partial) glycosylation o f the hormone. In contrast, cytoplasmic expression resulted in misfold ing and partial breakdown of the protein. The data demonstrate that sy nthesis, 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.