Vacuole accumulation of storage protein and lectin expressed in transgenic tobacco seeds

The expression of proteins in transgenic plants offers an elegant means to examine targeting signals used for transport to intracellular sites of accumulation. We have used electron microscopic immunogold procedures to localize several different storage proteins and lectins expressed in transgenic tobacco seeds. The objective of these studies is to characterize targeting signals which permit translocation and accumulation in protein storage vacuoles (protein bodies). Vacuolar proteins such as phaseolin and phytohemagglutinin (PHA) are correctly transported to the protein storage vacuoles of transgenic tobacco seeds. Site-directed mutagenesis was used to change Asn-linked glycosylation sites of PHA. Minus glycan PHA was accumulated in the protein storage vacuoles indicating that glycans do not confer targeting information. Zein the non-vacuolar storage protein of maize accumulates in the protein storage vacuoles indicating that deposition occurs in some proteins which may lack vacuolar targeting signals.