AUTHOR=Kojima Soichi , Minagawa Haruka , Yoshida Chika , Inoue Eri , Takahashi Hideki , Ishiyama Keiki 

TITLE=Coregulation of glutamine synthetase1;2 (GLN1;2) and NADH-dependent glutamate synthase (GLT1) gene expression in Arabidopsis roots in response to ammonium supply

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1127006

DOI=10.3389/fpls.2023.1127006

ISSN=1664-462X

ABSTRACT=<p>Ammonium absorbed by roots is assimilated into amino acids. The glutamine synthetase/glutamate synthase (glutamine 2-oxoglutarate aminotransferase) (GS/GOGAT) cycle is essential to this biological process. In <italic>Arabidopsis thaliana</italic>, <italic>GLN1;2</italic> and <italic>GLT1</italic> are the <italic>GS</italic> and <italic>GOGAT</italic> isoenzymes induced in response to ammonium supply and playing key roles in ammonium utilization. Although recent studies suggest gene regulatory networks involved in transcriptional regulation of ammonium-responsive genes, direct regulatory mechanisms for ammonium-induced expression of <italic>GS/GOGAT</italic> remain unclear. In this study, we revealed that the expression of <italic>GLN1;2</italic> and <italic>GLT1</italic> in Arabidopsis is not directly induced by ammonium but is regulated by glutamine or post-glutamine metabolites produced by ammonium assimilation. Previously, we identified a promoter region required for ammonium-responsive expression of <italic>GLN1;2</italic>. In this study, we further dissected the ammonium-responsive region of the <italic>GLN1;2</italic> promoter and also performed a deletion analysis of the <italic>GLT1</italic> promoter, which led to the identification of a conserved ammonium-responsive region. Yeast one-hybrid screening using the ammonium-responsive region of the <italic>GLN1;2</italic> promoter as a decoy sequence revealed a trihelix family transcription factor DF1 that binds to this region. A putative DF1 binding site was also found in the ammonium-responsive region of the <italic>GLT1</italic> promoter.</p>