Arabidopsis thaliana ASN2 encoding asparagine synthetase is involved in the control of nitrogen assimilation and export during vegetative growth |
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| Authors: | LAURE GAUFICHON CÉLINE MASCLAUX‐DAUBRESSE GUILLAUME TCHERKEZ MICHÈLE REISDORF‐CREN YUKIKO SAKAKIBARA TOSHIHARU HASE GILLES CLÉMENT JEAN‐CHRISTOPHE AVICE OLIVIER GRANDJEAN ANNE MARMAGNE STÉPHANIE BOUTET‐MERCEY MARIANNE AZZOPARDI FABIENNE SOULAY AKIRA SUZUKI |
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| Institution: | 1. INRA, UMR1318, Institut Jean‐Pierre Bourgin, Département Adaptation des Plantes à l'Environnement, RD10, F‐78000 Versailles, France;2. Institut de Biologie des Plantes, CNRS UMR 8618, Batiment 630, Université Paris Sud, 91405 Orsay cedex, France;3. Université Versailles Saint‐Quentin, 45 avenue des Etats‐Unis, 78035 Versailles cedex, France;4. Division of Protein Chemistry, Laboratory of Regulation of Biological Reactions, Institute for Protein Research, Osaka University, Japan;5. INRA, UMR1318, Institut Jean‐Pierre Bourgin, Plateau Technique Spécifique de Chimie du Végétal, RD10, F‐78000 Versailles, France;6. INRA, UMR 950, Ecophysiologie Végétale, Agronomie et Nutritions NCS, Institut de Biologie Fondamentale et Appliquée, SFR ICORE, Campus 1, Esplanade de la Paix, Université de Caen Basse‐Normandie, F‐14032 Caen cedex 05, France;7. INRA, UMR1318, Institut Jean‐Pierre Bourgin, Plateforme de Cytologie et d'Imagerie Végétale, RD10, F‐78000 Versailles, France;8. INRA, UMR1318, Institut Jean‐Pierre Bourgin, Laboratoire Commun de Biochimie, RD10, F‐78000 Versailles, France |
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| Abstract: | We investigated the function of ASN2, one of the three genes encoding asparagine synthetase (EC 6.3.5.4), which is the most highly expressed in vegetative leaves of Arabidopsis thaliana. Expression of ASN2 and parallel higher asparagine content in darkness suggest that leaf metabolism involves ASN2 for asparagine synthesis. In asn2‐1 knockout and asn2‐2 knockdown lines, ASN2 disruption caused a defective growth phenotype and ammonium accumulation. The asn2 mutant leaves displayed a depleted asparagine and an accumulation of alanine, GABA, pyruvate and fumarate, indicating an alanine formation from pyruvate through the GABA shunt to consume excess ammonium in the absence of asparagine synthesis. By contrast, asparagine did not contribute to photorespiratory nitrogen recycle as photosynthetic net CO2 assimilation was not significantly different between lines under both 21 and 2% O2. ASN2 was found in phloem companion cells by in situ hybridization and immunolocalization. Moreover, lack of asparagine in asn2 phloem sap and lowered 15N flux to sinks, accompanied by the delayed yellowing (senescence) of asn2 leaves, in the absence of asparagine support a specific role of asparagine in phloem loading and nitrogen reallocation. We conclude that ASN2 is essential for nitrogen assimilation, distribution and remobilization (via the phloem) within the plant. |
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| Keywords: | amino acid synthesis and metabolism cellular localization nitrogen assimilation and translocation reverse genetics |
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