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Plant and Cell Physiology Advance Access originally published online on June 29, 2009
Plant and Cell Physiology 2009 50(8):1532-1543; doi:10.1093/pcp/pcp098
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© The Author 2009. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Overexpression of BiP has Inhibitory Effects on the Accumulation of Seed Storage Proteins in Endosperm Cells of Rice

Hiroshi Yasuda1,2, Sakiko Hirose1,3, Taiji Kawakatsu1, Yuhya Wakasa1 and Fumio Takaiwa1,*

1Transgenic Crop Research and Development Center, National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki, 305-8602 Japan
2Research Team for Crop Cold Tolerance, National Agricultural Research Center for Hokkaido region, Hitsujigaoka 1, Toyohira-ku, Sapporo, Hokkaido, 062-8555 Japan
3Rice Biotechnology Research Team, National Institute of Crop Sciences, Kannondai 2-1-18, Tsukuba, Ibaraki, 305-8518 Japan

*Corresponding author: E-mail, takaiwa{at}nias.affrc.go.jp; Fax,+81-29-838-8397.


  Abstract

Seed storage proteins are specifically and highly synthesized during seed maturation and are deposited into protein bodies (PBs) via the endoplasmic reticulum (ER) lumen. The accumulation process is mediated by ER chaperones such as luminal binding protein (BiP) and protein disulfide isomerase (PDI). To examine the role of ER chaperones and the relationship between ER chaperones and levels of accumulation of seed storage proteins, we generated transgenic rice plants in which the rice BiP and PDI genes were overexpressed in an endosperm-specific manner under the control of the rice seed storage protein glutelin promoter. The seed phenotype of the PDI-overexpressing transformant was almost identical to that of the wild type, whereas overexpression of BiP resulted in transgenic rice seed that displayed an opaque phenotype with floury and shrunken features. In the BiP-overexpressing line, the levels of accumulation of seed storage proteins and starch contents were significantly lower compared with the wild type. Interestingly, overproduction of BiP in the endosperm of the transformant not only altered the morphological structure of ER-derived PB-I, but also generated unusual new PB-like structures composed of a high electron density matrix containing glutelin and BiP and a low electron density matrix containing prolamins. Notably, polysomes were attached around the aberrant PB-like structures, indicating that this aberrant structure is an ER-derived PB-I derivative. These results suggested that the PB-like structure may be formed in the ER lumen, resulting in inhibition of translation, folding and transport of seed proteins.

Keywords: BiP - Chaperone proteins - ER stress - PB - PDI - Quality control - Storage proteins

Abbreviations: BiP, binding protein; BSA, bovine serum albumin; CBB, Coomassie Brilliant Blue; DAF, days after flowering; ER, endoplasmic reticulum; GluB-1, rice glutelin B-1; PB-I/II, protein body type I/II; PBS, phosphate-buffered saline; PDI, protein disulfide isomerase; PSV, protein storage vacuole; RT–PCR, reverse transcription–PCR; SEM, scanning electron microscopy; TEM, transmission electron microscopy; UPR, unfolded protein response.

(Received May 22, 2009; Accepted June 25, 2009)
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