Journal Article

Three cytosolic glutamine synthetase isoforms localized in different-order veins act together for N remobilization and seed filling in Arabidopsis

Morin, Halima, H, Marmagne, Anne, Reisdorf-Cren, Michèle, Moison, Michaël, Avice, Jean-Christophe, Soulay, Fabienne, CETIOM (Centre Technique Interprofessionnel des Oleagineux Metropolitains); BAP department of INRA; LabEx Saclay Plant Sciences-SPS [ANR-10-LABX-0040-SPS], Ecophysiologie Végétale, Agronomie et Nutritions (EVA) ; Université de Caen Normandie (UNICAEN) ; Normandie Université (NU)-Normandie Université (NU)-Institut National de la Recherche Agronomique (INRA), Institut de Recherche en Horticulture et Semences (IRHS) ; Université d'Angers (UA)-Institut National de la Recherche Agronomique (INRA)-AGROCAMPUS OUEST, Citerne, Sylvie, Azzopardi, Marianne, Laboratoire d'Ecologie Alpine (LECA) ; Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Masclaux-Daubresse, Céline, Lothier, Jeremy, Institut Jean-Pierre Bourgin (IJPB) ; Institut National de la Recherche Agronomiq

2018

Overview

Glutamine synthetase (GS) is central for ammonium assimilation and consists of cytosolic (GS1) and chloroplastic (GS2) isoenzymes. During plant ageing, GS2 protein decreases due to chloroplast degradation, and GS1 activity increases to support glutamine biosynthesis and N remobilization from senescing leaves. The role of the different Arabidopsis GS1 isoforms in nitrogen remobilization was examined using 15N tracing experiments. Only the gln1;1-gln1; 2-gln1; 3 triple-mutation affecting the three GLN1;1, GLN1;2, and GLN1; 3 genes significantly reduced N remobilization, total seed yield, individual seed weight, harvest index, and vegetative biomass. The triple-mutant accumulated a large amount of ammonium that could not be assimilated by GS1. Alternative ammonium assimilation through asparagine biosynthesis was increased and was related to higher ASN2 asparagine synthetase transcript levels. The GS2 transcript, protein, and activity levels were also increased to compensate for the lack of GS1-related glutamine biosynthesis. Localization of the different GLN1 genes showed that they were all expressed in the phloem companion cells but in veins of different order. Our results demonstrate that glutamine biosynthesis for N-remobilization occurs in veins of all orders (major and minor) in leaves, it is mainly catalysed by the three major GS1 isoforms (GLN1; 1, GLN1; 2, and GLN1; 3), and it is alternatively supported by AS2 in the veins and GS2 in the mesophyll cells.

• Publisher: Oxford University Press (OUP),CCSD,Oxford University Press
• Subject: ammonium / Arabidopsis / asparagine / aspartate-ammonia ligase / biomass / biosynthesis / catalytic activity / chloroplasts / filling period / genes / glutamate-ammonia ligase / glutamine / harvest index / isotope labeling / isozymes / leaves / Life Sciences / mesophyll / nitrogen / phloem companion cells / Research Papers / seed weight / seed yield / stable isotopes / Vegetal Biology
• ISBN: 0004423096000