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

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 AtGLR1.11-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.