Poster: Protein Targeting & Vesicular Trafficking

Abs # 1173: Rice mutant glup3 greatly accumulates the glutelin precursor in protein storage vacuole and deletes the vacuolar processing enzyme

Presenter:	Kumamaru, Toshihiro , kumamaru@agr.kyushu-u.ac.jp
Authors	Kumamaru, Toshihiro  (A)   Uemura, Yuji  (A)   Takemoto, Yoko  (A)   Ogawa, Masahiro  (B)   Hara-Nishimura, Ikuko  (C)   Satoh, Hikaru  (A)
Affiliations:	(A): Institute of Genetic Resources, Faculty of Agriculture, Kyushu University (B): Faculty of Human Life Science, Yamaguchi Prefectural University (C): Department of Botany, Graduate School of Science, Kyoto University

Rice seed glutelins are initially synthesized as proglutelin on the endoplasmic reticulum, and then transported into the protein storage vacuole (PSV), where it is accumulated as the cleaved form. Little information is known about the genes that regulate the above pathway. To clarify the function of genes participating in the glutelin biosynthesis, we induced several mutants accumulating greatly proglutelin by N-methyl-N-nitrosurea treatment. In the present study, to identify the intracellular organelle where proglutelin is cleaved and the enzyme participating in cleavage, glup3 mutant was analyzed. PSV in glup3 mutant accumulated proglutelin as well as the cleaved glutelin, suggesting that proglutelin is transported into PSV and the glup3 mutation involves in the cleavage of it. To identify the key gene for glup3 mutation, the high-resolution linkage map of Glup3 gene was constructed. A homology search with the deduced amino acid in the delimited genomic region revealed a sequence with significant homology to vacuolar processing enzyme (VPE), and the sequence was regarded as Glup3 candidate. The sequencing of candidate gene in three independent glup3 lines revealed the single amino acid substitution or the formation of stop codon in the coding region. The transcript of candidate gene was not expressed in the glup3 mutant. The VPE activity in the developing seeds from all glup3 lines reduced remarkably as compared with wild-type. These results suggest strongly that Glup3 gene encodes the VPE. We conclude that proglutelin transported into the PSV is cleaved proteolytically into two subunits and finally accumulated in the PSV, and the VPE is essential for the cleavage of proglutelin in the PSV.