Poster: Protein targeting & vesicular trafficking

Abs # 652: A receptor-mediated transport of seed storage proteins in Arabidopsis thaliana

Presenter:	Shimada, Tomoo , tshimada@gr.bot.kyoto-u.ac.jp
Authors	Shimada, Tomoo  (A)   Fuji, Kentaro  (A)   Tamura, Kentaro  (A)   Kondo, Maki  (B)   Nishimura, Mikio  (B)   Hara-Nishimura, Ikuko  (A)
Affiliations:	(A): Graduate School of Science, Kyoto University (B): Department of Cell Biology, National Institute for Basic Biology

Seeds of higher plants accumulate large quantities of storage proteins in protein storage vacuoles (PSVs). During seed maturation, storage protein precursors synthesized on rER are sorted to PSVs, where they are converted into the mature forms and accumulated. Previously, we identified a type I integral membrane protein, designated PV72, as a putative receptor responsible for the sorting of storage proteins in maturing pumpkin seeds (1). Here, we show crucial evidence that AtVSR1/AtELP, one of PV72 homologs in Arabidopsis, functions as a sorting receptor for seed storage proteins in Aradidopsis seeds (2). The atvsr1 seeds abnormally accumulate the precursors of 12S globulin and 2S albumin, together with the mature forms of these proteins. The atvsr1 mutant mis-sorts storage proteins by secreting them from cells, resulting in an enlarged and electron-dense extracellular space in the seeds. AtVSR1 was found to bind to the C-terminal peptide of 12S globulin in a Ca²⁺-dependent manner. These findings demonstrate a receptor-mediated transport of seed storage proteins to PSVs. (1) T. Shimada et.al. (2002) Plant Cell Physiol. 43, 1086-1095. (2) T. Shimada et al. (2003) Proc. Natl. Acad. Sci. USA, 100, 16095-16100.