Protein Targeting and Vesicular Trafficking
Satoh, mio , Masako, Fukuda , Nagamine, Ai , Washida, Haruhiko , Sugino, Aya , Ogawa, Masahiro , Satoh, Hikaru , Okita, Thomas W , Kumamaru, Toshihiro .
Rab5a plays a critical role in the transport of the rice glutelin to protein storage vacuole.
The rice seed storage proteins, prolamin and glutelin, are synthesized on distinct subdomains of the endoplasmic reticulum (ER). Prolamins are retained within the ER lumen whereas glutelins are exported to the protein storage vacuole (PSV). We have identified several N-methyl-N-nitrosurea-induced mutants, which over-accumulate the glutelin precursor. To identify the basis for the abnormal glutelin precursor levels, a high-resolution genetic linkage map of one mutant, glup4, was constructed. A homology search of the deduced amino acid in the delimited genomic region revealed a sequence with significant homology to the GTPase Rab5a. This initial assignment was verified by sequencing three independent glup4 alleles which contained missense or nonsense mutations in the coding region. Rab5a is required for vesicular transport in yeast, mammalian and Arabidopsis during early endosome formation, suggesting that Rab5a participates in the intracellular transport of glutelin precursor. Immunofluorescent and immunoelectron microscopy of developing endosperm of glup4 mutant showed a disruption in glutelin transport to the vacuole. Glutelin was found to be secreted and contained within cytoplasmic protein inclusions much smaller than normal PSVs as well as large, highly dilated ER membrane complexes. These results indicated that the rice Rab5a plays critical role for normal glutelin transport to the PSV. Alternatively, as glutelin RNAs are mis-localized from the cisternal-ER to protein body-ER, Rab5a may also be essential for glutelin RNA transport and localization.
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1 - Kyushu University, JAPAN
2 - Washington State University
3 - Yamaguchi Prefectural University, JAPAN
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM