Poster: Seed Biology

Abs # 546: Transport and processing of seed storage proteins in higher plants

Presenter:	Shimada, Tomoo , tshimada@gr.bot.kyoto-u.ac.jp
Authors	Shimada, Tomoo  (A)   Fuji, Kentaro  (A)   Li, Lixin  (A)   Kataoka, Miyuki  (A)   Yamada, Kenji  (B)   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

Seed storage proteins are deposited in protein bodies, specialized vacuoles, as a source of nitrogen for the growth after seed germination. They are synthesized on rER as larger precursors, are transported into protein storage vacuoles by vesicle-mediated machinery and then are processed by VPE ( vacuolar processing enzyme) to make mature forms. In maturing pumpkin seeds, PAC ( precursor- accumulating) vesicles mediate the intracellular transport of the precursors of storage proteins. We have found a vacuolar sorting receptor PV72 as a major component on the membrane of the isolated PAC vesicles. Arabidopsis mutants that exhibited abnormal accumulation of the precursors of storage proteins were identified by immunoblot analysis using antibodies against either 12S globulin or 2S albumin. The dry seeds of several mutant lines were revealed to lack bVPE, a seed type VPE. Mutations were found within the gene encoding bVPE in these mutants. Therefor, these mutants appeared to have a defect in the processing step in the vacuoles. Interestingly, the processing was only partially affected in the mutants, suggesting the other proteinases are also involved in the processing step of storage proteins. Some of mutants contained bVPE in dry seeds as wild type did. It is possible that they have defects in the transport steps to the vacuoles.