THE PLANT CELL, Vol 2, Issue 4 345-355, Copyright © 1990 by American Society of Plant Biologists
Expression of Mutant Patatin Protein in Transgenic Tobacco Plants: Role of Glycans and Intracellular Location
U. Sonnewald, A. von Schaewen and L. Willmitzer
Institut fur Genbiologische Forschung Berlin GmbH, Ihnestrasse 63, D-1000 Berlin 33, Federal Republic of Germany
The influence of N-glycosylation and subcellular compartmentation on
various characteristics of a vacuolar glycoprotein is described. One member
of the patatin gene family was investigated as a model system. Different
glycosylation mutants obtained by destroying the consensus site
Asn-X-Ser/Thr by oligonucleotide-directed mutagenesis were expressed in
leaves of transgenic tobacco plants under the control of a light-inducible
promoter. The various patatin glycomutants retained their properties in
comparison with the wild-type protein with respect to protein stability,
subcellular compartmentation, enzymatic activity, and various
physicochemical properties studied showing the N-glycosylation not to be
essential for any of these characteristics. To test the importance of the
co-translational transport and the subcellular (vacuolar) location for the
properties of the patatin protein, another mutant was constructed in which
the signal peptide was deleted, leading to its synthesis and accumulation
in the cytosol. Biochemical analysis of this protein in comparison with its
vacuolar form again revealed no significant differences with respect to its
enzymatic activity or its stability in normal vegetative cells. During seed
development, however, the cytoplasmic form was more stable than the
vacuolar form, indicating the appearance of proteases specific for the
protein bodies of developing seeds.
