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Plant Physiology Preview Published on April 21, 2006; 10.1104/pp.106.076661
Received January 5, 2006 The intracellular fate of a recombinant protein is tissue-dependent
Institute for Molecular Biotechnology, Biology VII, Aachen University, Worringerweg 1, 52074 Aachen, Germany * Corresponding author; email: eva.stoger{at}molbiotech.rwth-aachen.de.
Recombinant proteins directed to the secretory pathway in plants require a signal peptide for entry into the endoplasmic reticulum. In the absence of further targeting information, such proteins are generally secreted via the default pathway to the apoplast. This has been well-documented in protoplasts and leaf tissue, but the trafficking of recombinant proteins in seeds and other storage tissues has rarely been investigated. We used Aspergillus niger phytase as a model glycoprotein to compare the intracellular fate of a recombinant protein in the leaves and seeds of rice. Using fluorescence and electron microscopy, we showed that the recombinant protein was efficiently secreted from leaf cells as expected. In contrast, within endosperm cells it was retained in ER-derived prolamin bodies and protein storage vacuoles. Consistent with our immunolocalization data, the phytase produced in endosperm cells possessed oligomannose and vacuolar-type N-glycans (Man3(Xyl)(Fuc)GlcNAc2), whereas the phytase produced in leaves contained predominantly secretion-type N-glycans (GlcNAc2Man3(Xyl)(Fuc)GlcNAc2). The latter could not be detected in preparations of the endosperm-derived phytase. Our results show that the intracellular deposition and modification of a recombinant protein is tissue dependent.
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