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The putative glutamate receptor 1.1 (AtGLR1.1) functions as a regulator of carbon and nitrogen metabolism in Arabidopsis thaliana.

ABSTRACT: The ability to coordinate carbon (C) and nitrogen (N) metabolism enables plants to regulate development and metabolic responses to different environmental conditions. The regulator(s) or sensor(s) that monitor crosstalk between biosynthetic pathways and ultimately control the flow of C or N through them have remained elusive. We used an antisense strategy to demonstrate that the putative glutamate receptor 1.1 (AtGLR1.1) functions as a regulator of C and N metabolism in Arabidopsis. Seeds from AtGLR1.1-deficient Arabidopsis (antiAtGLR1.1) lines did not germinate in the presence of an animal ionotropic glutamate receptor (iGLR) antagonist, but germination was restored upon coincubation with an iGLR agonist or the putative ligand glutamate. In antiAtGLR1.1 lines, endogenous abscisic acid (ABA) concentrations increased with iGLR antagonist treatments and decreased with coincubation with an iGLR agonist, suggesting that germination was controlled by ABA. antiAtGLR1.1 seedlings also exhibited sensitivity to increased levels of Ca2+ compared with wild type, and they exhibited a conditional phenotype that was sensitive to the C:N ratio. In the presence of C, specifically sucrose, but not glucose, mannitol, or sorbitol, antiAtGLR1.1 seeds did not germinate, but germination was restored upon coincubation with NO3-, but not NH4+. Immunoblot, isoenzyme, and RT-PCR analyses indicate that AtGLR1.1 regulates the accumulation of distinct C- and N-metabolic enzymes, hexokinase 1 (HXK1) and zeaxanthin epoxidase (ABA1), by transcriptional control. We provide a model to describe the role of AtGLR1.1 in C/N metabolism and ABA biosynthesis, which in turn controls seed germination.

SUBMITTER: Kang J

PROVIDER: S-EPMC164539 | biostudies-literature | 2003 May

REPOSITORIES: biostudies-literature

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Publications

The putative glutamate receptor 1.1 (AtGLR1.1) functions as a regulator of carbon and nitrogen metabolism in Arabidopsis thaliana.

Kang Jiman J Turano Frank J FJ

Proceedings of the National Academy of Sciences of the United States of America 20030508 11

The ability to coordinate carbon (C) and nitrogen (N) metabolism enables plants to regulate development and metabolic responses to different environmental conditions. The regulator(s) or sensor(s) that monitor crosstalk between biosynthetic pathways and ultimately control the flow of C or N through them have remained elusive. We used an antisense strategy to demonstrate that the putative glutamate receptor 1.1 (AtGLR1.1) functions as a regulator of C and N metabolism in Arabidopsis. Seeds from A ...[more]

PMID: 12738881

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Project description:Glutamate dehydrogenase (GDH) releases ammonia in a reversible NAD(P)+-dependent oxidative deamination of glutamate that yields 2-oxoglutarate (2OG). In current perception, GDH contributes to Glu homeostasis and plays a significant role at the junction of carbon and nitrogen assimilation pathways. GDHs are members of a superfamily of ELFV (Glu/Leu/Phe/Val) amino acid dehydrogenases and are subdivided into three subclasses, based on coenzyme specificity: NAD+-specific, NAD+/NADP+ dual-specific, and NADP+-specific. We determined in this work that the mitochondrial AtGDH1 isozyme from A. thaliana is NAD+-specific. Altogether, A. thaliana expresses three GDH isozymes (AtGDH1-3) targeted to mitochondria, of which AtGDH2 has an extra EF-hand motif and is stimulated by calcium. Our enzymatic assays of AtGDH1 established that its sensitivity to calcium is negligible. In vivo the AtGDH1-3 enzymes form homo- and heterohexamers of varied composition. We solved the crystal structure of recombinant AtGDH1 in the apo-form and in complex with NAD+ at 2.59 and 2.03 Å resolution, respectively. We demonstrate also that both in the apo form and in 1:1 complex with NAD+, it forms D 3-symmetric homohexamers. A subunit of AtGDH1 consists of domain I, which is involved in hexamer formation and substrate binding, and of domain II which binds coenzyme. Most of the subunits in our crystal structures, including those in NAD+ complex, are in open conformation, with domain II forming a large (albeit variable) angle with domain I. One of the subunits of the AtGDH1-NAD+ hexamer contains a serendipitous 2OG molecule in the active site, causing a dramatic (?25°) closure of the domains. We provide convincing evidence that the N-terminal peptide preceding domain I is a mitochondrial targeting signal, with a predicted cleavage site for mitochondrial processing peptidase (MPP) at Leu17-Leu18 that is followed by an unexpected potassium coordination site (Ser27, Ile30). We also identified several MPD [(+/-)-2-methyl-2,4-pentanediol] binding sites with conserved sequence. Although AtGDH1 is insensitive to MPD in our assays, the observation of druggable sites opens a potential for non-competitive herbicide design.

Dataset Information

The putative glutamate receptor 1.1 (AtGLR1.1) functions as a regulator of carbon and nitrogen metabolism in Arabidopsis thaliana.

Publications

The putative glutamate receptor 1.1 (AtGLR1.1) functions as a regulator of carbon and nitrogen metabolism in Arabidopsis thaliana.

Similar Datasets

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