Washida, Haruhiko , Sugino, Aya , Kaneko, Sachiyo , Okita, Thomas W .
Identification of zip codes required for the cisternal ER targeting of rice glutelin RNA.
RNA localization is utilized for the synthesis of distinct classes of storage proteins and their efficient packaging within separate endomembrane compartments in developing rice endosperm cells. Prolamine RNAs are targeted to the spherical protein body ER (PB-ER) which bounds the newly assembled prolamine polypeptides (PB) whereas glutelin RNAs are enriched on adjacent cisternal ER. Following translocation into the ER lumen, glutelin precursors are routed via the Golgi to the protein storage vacuole (PSV). Ongoing studies have shown that these RNAs are targeted to these ER subdomains by regulated RNA transport pathways requiring specific RNA zip code sequences with the glutelin signals functionally dominant to the prolamine signals. We set out to identify the glutelin zip codes by their capacity to re-direct the localization of a maize 10 kD zein RNA (which contains multiple PB-ER zip codes) to the cisternal ER. Analysis of transgenic rice plants expressing various hybrid zein-glutelin RNAs by in situ RNA localization analysis showed that the glutelin transcript contains at least three cisternal ER targeting zip codes. One zip code is located within proximal half of exon 1, while two lie within exon 4 which includes the 3'UTR. Further detailed analysis of exon 4 revealed that one zipcode is located within the gene coding region and while the other is located on the distal half of the 3'UTR. In addition to RNA localization, we also studied where the zein polypeptides were deposited in these various transgenic plants. Immuno-cytological studies at the light and electron microscopy levels demonstrated that when the zein RNAs were targeted to the PB-ER their proteins were stored within the prolamine PBs. When the zein RNAs were mis-targeted to the cisternal ER, however, the proteins were observed within the protein storage vacuoles (PSVs). Our result indicates a close relationship between RNA and protein localization and provides the underlying basis for the variable use of the ER lumen or PSV as the site of storage protein deposition among flowering plants.
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1 - Washington State University
Presentation Type: ASPB Minisymposium
Location: Continental B/Hilton
Date: Monday, July 9th, 2007
Time: 9:45 AM