Plant and Cell Physiology Advance Access published online on June 20, 2009
Plant and Cell Physiology, doi:10.1093/pcp/pcp092
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Regulation of HSD1 in seeds of Arabidopsis thaliana

1Institut Jean-Pierre Bourgin, UMR Biologie des semences, INRA/AgroParisTech, F-78000 Versailles, France.
2CBAI, UMR Chimie Biologique, INRA/AgroParisTech, F-78850 Thiverval-Grignon, France.
3Institut Jean-Pierre Bourgin, Plateforme de cytologie et imagerie végétale INRA-IJPB, F-78000 Versailles, France.
Corresponding author: Martine Miquel, Institut Jean-Pierre Bourgin, UMR Biologie des Semences, INRA'AgroParisTech, F-78000 Versailles, France. Tel. +33 1 30 83 33 20, Fax +33 1 30 83 31 11, E-mail. Martine.Miquel{at}versailles.inra.fr
| Abstract |
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The hydroxysteroid dehydrogenase HSD1, identified in the proteome of oil bodies from mature Arabidopsis seeds, is encoded by At5g50600 and At5g50700, two gene copies anchored on a duplicated region of chromosome 5. Using a real-time quantitative reverse transcriptase (RT)-PCR approach, the accumulation of HSD1 mRNA was shown to be specifically and highly induced in oil-accumulating tissues of maturing seeds. HSD1 mRNA disappeared during germination. The activity of HSD1 promoter and the localization of HSD1 transcripts by in situ hybridization were consistent with this pattern. A complementary set of molecular and genetic analyses showed that HSD1 is a target of LEAFY COTYLEDON2, a transcriptional regulator able to bind the promoter of HSD1. Immunoblot analyses and immunolocalization experiments using anti-AtHSD1 antibodies established that the pattern of HSD1 deposition was faithfully reflecting mRNA accumulation. At the subcellular level, the study of HSD1:GFP fusion proteins showed the targeting of HSD1 to the surface of oil bodies. Transgenic lines over expressing HSD1 were then obtained to test the importance of a proper transcriptional regulation of HSD1 in seeds. Whereas no impact on oil accumulation could be detected, transgenic seeds exhibited lower cold and light requirements to break dormancy, germinate, and mobilize storage lipids. Interestingly, over expressors of HSD1 over accumulated HSD1 protein in seeds but not in vegetative organs, suggesting that post-transcriptional regulations exist that prevent HSD1 accumulation in tissues deprived of oil bodies.
Keywords: Arabidopsis thaliana - hydroxysteroid dehydrogenase 1 - LEAFY COTYLEDON2 - oil bodies - seed - triacylglycerol
* SB and NRD have contributed equally to this work and should be both regarded as the first author.
Present address: Laboratoire de Virologie Moléculaire et Structurale, UMR CNRS 2472, Bât. 14B, 1 Avenue de la Terrasse, F-91198 Gif-sur-Yvette Cedex, France.
(Received May 14, 2009; Accepted June 19, 2009)
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