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 Ca 2؉ 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 NO 3 ؊ , but not NH 4 ؉ . 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 C͞N metabolism and ABA biosynthesis, which in turn controls seed germination.

Primary N-assimilation into Amino Acids in Arabidopsis

“…In fact, some reports claim that the cellular carbon to nitrogen ratio is a major player in the metabolic control of nitrogen assimilation (Coruzzi and Zhou, 2001;Foyer et al, 2003). Plant glutamate receptors uncovered by have also been implicated in sensing changes in Glu and in C/N levels (Kang and Turano, 2003). In the case of N-assimilation gene expression, the notion that plants sense C:N ratio is supported by the data which shows that the carbon induction of GLN2 is reversed by the addition of organic N, while the carbon repression of ASN1 is relieved by the addition of organic N (Lam et al, 1994;Oliveira and Coruzzi, 1999) (Fig.…”

Cycads: evolutionary innovations and the role of plant-derived neurotoxins

“…Isolated Arabidopsis mutants resistant to the effects of BMAA might identify the endogenous components of a BMAAtargeted pathway in Arabidopsis [59]. Evidence indicates that BMAA acts as an agonist of an Arabidopsis glutamate receptor gene (GLR1.1) [60].…”

Inter-subunit interactions between Glutamate-Like Receptors inArabidopsis

“…16 The predicted membrane topology and orientation of the protein as a tetramer, with the ATD and LBD exposed to the external side of the membrane, are considered to be conserved in plant GLRs. 17 Understanding the function of plant GLRs has previously been hampered by gene redundancy and toxicity although genetic, pharmacological, and electrophysiological approaches suggested diverse physiological roles such as carbon/nitrogen balance regulation, 18,19 stomatal opening, 20 pollen tube growth, 21 plant-pathogen interaction, [22][23][24] responses to wound, 25,26 and lateral root formation. 12 Recently, 2 of the Arabidopsis GLRs, AtGLR3.4 and 1.4, were shown to function as amino acid gated channels when expressed in heterologous systems, 13,27 further confirming the functional commonality of plant and mammalian glutamate receptors.…”