THE PLANT CELL, Vol 1, Issue 1 95-104, Copyright © 1989 by American Society of Plant Biologists
In Vitro Mutated Phytohemagglutinin Genes Expressed in Tobacco Seeds: Role of Glycans in Protein Targeting and Stability
T. A. Voelker, E. M. Herman and M. J. Chrispeels
Department of Biology, University of California, San Diego, La Jolla, California 92093-0116
Phytohemagglutinin is a glycoprotein that accumulates in the protein
storage vacuoles of bean seeds. The mature glycoprotein has a high-mannose
and a complex glycan. We describe here the use of site-directed mutagenesis
and expression of the mutated genes in transgenic tobacco to study the role
of glycans in intracellular targeting. The reading frame for
phytohemagglutinin-L was mutated so that either one or both of the
glycosylation signals were disrupted to specifically prevent the attachment
of asparagine-linked glycans. Expression of these genes with the
[beta]-phaseolin promoter in the seeds of transgenic tobacco plants showed
that phytohemagglutinin-L with only one glycan or without glycans was
correctly targeted to the protein storage vacuoles of the seeds.
Furthermore, the absence of either the complex glycan or the high-mannose
glycan did not alter the processing of the other glycan. On the basis of
these results, we propose that the targeting signal of this vacuolar
protein is contained in its polypeptide domain and not in its glycans.
