Two Closely Related Wheat Storage Proteins Follow a Markedly Different Subcellular Route in Xenopus laevis Oocytes.

Abstract

[alpha]-Gliadins and [gamma]-gliadins are two closely related wheat storage proteins that evolved from a common ancestral gene. However, synthesis of [alpha]-gliadins and [gamma]-gliadins in Xenopus laevis oocytes revealed striking differences in their subcellular routing. The major portion of [alpha]-gliadin accumulated inside the oocyte, whereas most of the [gamma]-gliadin was secreted. Disruption of the Golgi apparatus by monensin revealed that the major part of secretion of [gamma]-gliadin is Golgi mediated. The difference in the subcellular route between [alpha]-gliadin and [gamma]-gliadin may be attributed to differential transport from the endoplasmic reticulum to the Golgi apparatus, a process that is generally the rate-limiting step in protein secretion. Coinjection of the two mRNAs had no effect on their routing, indicating no interaction between them. Our results support the hypothesis that subcellular transport of gliadins in wheat endosperm occurs in two separate routes; one is Golgi mediated, and the other is not. We also show that the subcellular transport may be markedly affected by small structural variations within closely related storage proteins.

Wheat (Triticum aestivum L.) [gamma]-Gliadin Accumulates in Dense Protein Bodies within the Endoplasmic Reticulum of Yeast

“…Moreover, a maize a-zein that was expressed in yeast accumulated within the ER of these cells (Coraggio et al, 1988). Accumulation of the 7-gliadin within the ER of the yeast cells was much more effective than that of a similar 7-gliadin expressed in Xenopus oocytes, where 50 to 80% of the protein was secreted via the Golgi to the medium (Simon et al, 1990;Altschuler et al, 1993). One possible explanation for this is that the 7-gliadin was not folded correctly within the ER of the yeast.…”

“…This supports our suggestion that retention of the 7-gliadin within the ER was not related to the phenomenon of oligomer formation during extraction. Thus, it seems likely that the efficient retention of the 7-gliadin within the ER of the yeast cells was related to the process of PB formation or to specific interactions of this protein with ER-resident proteins, such as BiP or other Ca 2+ -binding reticuloplasmins (Both and Koch, 1989;Sambrook, 1990;Simon et al, 1990;Suzuki et al, 1991). Such processes are apparently dictated by the N-terminal region of this protein.…”

“…We have recently expressed in Xenopus laevis oocytes two wheat storage proteins, a-and y-gliadins (Simon et al, 1990), and showed them to be partly retained within the oocytes, apparently within the ER, and partly secreted via the Golgi into the medium. The two storage proteins were secreted at considerably different rates.…”

Role of structural domains for maize ?-zein retention in Xenopus oocytes

“…Recent experiments by Ceriotti et al (1992) show that trimerization of the phaseolin subunits (a storage protein in bean seeds) is required for the transport of the protein out of the ER in Xenopus oocytes. By expressing a-and ]3-gliadins in Xenopus oocytes, Simon et al (1990) indicated the presence of two different routes for the transport of these wheat storage proteins from the ER to the vacuoles.…”

Two Structural Domains Mediate Two Sequential Events in [gamma]-Zein Targeting: Protein Endoplasmic Reticulum Retention and Protein Body Formation.

“…In wheat seed, storage proteins are deposited in two different types of PBs inside vacuoles (Rubin et al, 1992). Two separate routes to the vacuole have been postulated with regard to the transport of gliadins and glutelins: one is via the Golgi complex and the other is by way of an autophagy-like pathway (Simon et al, 1990;Levanony et al, 1992). Noncovalent interaction and disulfide bond cross-links between glutelins and/or gliadins seem to direct PB formation in the wheat endosperm (Shani et al, 1992).…”