JXB Advance Access originally published online on August 5, 2009
Journal of Experimental Botany 2009 60(14):4015-4027; doi:10.1093/jxb/erp235
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© 2009 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)
RESEARCH PAPER |
' Subunit of soybean β-conglycinin forms complex with rice glutelin via a disulphide bond in transgenic rice seeds*
1Laboratory of Food Quality Design and Development, Graduate School of Agriculture, Kyoto University, Gokasho, Uji, Kyoto, Japan 611-0011
2Department of Plant Biotechnology, National Institute of Agrobiological Sciences, Tsukuba, Japan 305-8602
To whom correspondence should be addressed: E-mail: marunobu{at}kais.kyoto-u.ac.jp
The 
' and β subunits of soybean β-conglycinin were expressed in rice seeds in order to improve the nutritional and physiological properties of rice as a food. The ' subunit accumulated in rice seeds at a higher level than the β subunit, but no detectable difference in mRNA transcription level between subunits was observed. Sequential extraction results indicate that the ' subunit formed one or more disulphide bonds with glutelin. Electron microscopic analysis showed that the ' subunit and the β subunit were transported to PB-II together with glutelin. In mature transgenic seeds, the β subunit accumulated in low electron density regions in the periphery of PB-II, whereas the ' subunit accumulated together with glutelin in high-density regions of the periphery. The subcellular localization of mutated ' subunits lacking one cysteine residue in the N-terminal mature region ('
Cys1) or five cysteine residues in the pro and N-terminal mature regions ('Cys5) were also examined. Low-density regions were formed in PB-II in mature seeds of transgenic rice expressing 'Cys 5 and 'Cys1. 'Cys5 was localized only in the low-density regions, whereas 'Cys1 was found in both low- and high-density regions. These results suggest that the ' subunit could make a complex via one or more disulphide bonds with glutelin and accumulate together in PB-II of transgenic rice seeds.
Key words: Disulphide bond, glutelin, rice, soybean
* This paper is dedicated to the memory of Professor Utsumi who passed away on 1 December 2008. He leaves a legacy of many important contributions on the biology of seeds and seed storage proteins.
Present address: Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164-6340, USA.
Received 13 March 2009; Revised 3 June 2009 Accepted 6 July 2009