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ARS Home » Research » Publications at this Location » Publication #129433
Title: EXPRESSION PATTERNS OF GENES ENCODING ENDOMEMBRANCE PROTEINS SUPPORT A REDUCED FUNCTION OF THE GOLGI IN WHEAT ENDOSPERM DURING THE ONSET OF STORAGE PROTEIN DEPOSITION.

Author
item SHY, GALIA - REHOVOT ISREAL
item EHLER, LINDA
item HERMAN, ELIOT
item GALILI, GAD - REHOVOT ISREAL

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: It has been proposed that the proteins accumulated in wheat seeds are assembled and accumulated by a novel mechanism whereby the proteins are aggregated into an inert vesicle that is deposited in a protein storage organelle using a mechanism that bypasses the usual path by which proteins move through a cell. The basis for this proposal is microscopic observations by coauthor Galili. An interpretation of this model predicts that the expression of certain genes should be repressed while other genes should be induced because of this bypass mechanism of protein accumulation. We isolated clones for the genes predicted to be regulated and tested the model using these clones. The resulting data supported the contention that wheat seeds use a novel means to accumulate seed proteins. Understanding how wheat seeds are formed becomes increasingly important as scientists focus on using biotechnology to alter seed composition because the biology of how seeds are formed presents opportunities and constraints that must be addressed as bioengineering objectives are developed. The information contained in this paper should be of broad interest to academic, industrial and government investigators concerned with how wheat seeds develop and are formed.

Technical Abstract: Wheat storage proteins are deposited in the vacuole of maturing endosperm cells by a novel pathway that is the result of protein body formation by the endoplasmic reticulum followed by autophagy into the central vacuole. This pathway provides a mechanism for hydrophobic storage protein complexes to be sequestered in the vacuole thereby by-passing the Golgi apparatus. This model predicts a reduced role of the Golgi in storage protein accumulation which has been supported by electron microscopy observations indicating that few Golgi are observed in maturing endosperm cells. To study the role of the endomembrane system in the transport and deposition of wheat storage proteins, we cloned and characterized wheat cDNAs encoding three distinct proteins of the endomembrane system; homologues of the ER translocon component Sec61a, the vacuolar sorting receptor BP-80, which is located in the Golgi and clathirn-coated prevacuole vesicles (CCV); and the Golgi COPI coatomer component COPa. During endosperm development, the levels of all three mRNAs were highest in young stages, before the onset of storage protein synthesis, and declined with seed maturation. However, the relative mRNA levels of BP-80/Sec61a and the COPa/Sec61a were lower during the onset of storage protein synthesis than at earlier stages of endosperm development. These results support previous studies, suggesting a reduced function of the Golgi apparatus in wheat storage protein transport and deposition.