WHEAT (TRITICUM-AESTIVUM L) GAMMA-GLIADIN ACCUMULATES IN DENSE PROTEIN BODIES WITHIN THE ENDOPLASMIC-RETICULUM OF YEAST

Following their sequestration into the endoplasmic reticulum (ER), whe at storage proteins may either be retained and packaged into protein b odies within this organelle or transported via the Golgi to vacuoles. We attempted to study the processes of transport and packaging of whea t storage proteins using the heterologous expression system of yeast. A wild-type wheat gamma-gliadin, expressed in the yeast cells, accumul ated mostly within the ER and was deposited in protein bodies with sim ilar density to natural protein bodies from wheat endosperm. This sugg ested that wheat storage proteins contain sufficient information to in itiate the formation of protein bodies in the ER of a heterologous sys tem. Only a small amount of the gamma-gliadin was transported to the y east vacuoles. When a deletion mutant of the gamma-gliadin, lacking th e entire N-terminal repetitive region, was expressed in the yeast cell s, the mutant was unable to initiate the formation of protein bodies w ithin the ER and was completely transported to the yeast vacuole. This strongly indicated that the information for packaging into dense prot ein bodies within the ER resides in the N-terminal repetitive region o f the gamma-gliadin. The advantage of using yeast to identify the sign als and mechanisms controlling the transport of wheat storage proteins and their deposition in protein bodies is discussed.