Arabidopsis Mutants Resistant to S(+)-β-Methyl-α, β-Diaminopropionic Acid, a Cycad-Derived Glutamate Receptor Agonist

Abstract

Ionotropic glutamate receptors (iGluRs) are ligand-gated ion channels that are the predominant neuroreceptors in the mammalian brain. Genes with high sequence similarity to animal iGluRs have been identified in Arabidopsis. To understand the role of Arabidopsis glutamate receptor-like (AtGLR) genes in plants, we have taken a pharmacological approach by examining the effects of BMAA [S(ϩ)-␤-methyl-␣, ␤-diaminopropionic acid], a cycad-derived iGluR agonist, on Arabidopsis morphogenesis. When applied to Arabidopsis seedlings, BMAA caused a 2-to 3-fold increase in hypocotyl elongation and inhibited cotyledon opening during early seedling development. The effect of BMAA on hypocotyl elongation is light specific. Furthermore, BMAA effects on early morphogenesis of Arabidopsis can be reversed by the simultaneous application of glutamate, the native iGluR agonist in animals. To determine the targets of BMAA action in Arabidopsis, a genetic screen was devised to isolate Arabidopsis mutants with a BMAA insensitive morphology (bim). When grown in the light on BMAA, bim mutants exhibited short hypocotyls compared with wild type. bim mutants were grouped into three classes based on their morphology when grown in the dark in the absence of BMAA. Class-I bim mutants have a normal, etiolated morphology, similar to wild-type plants. Class-II bim mutants have shorter hypocotyls and closed cotyledons when grown in the dark. Class-III bim mutants have short hypocotyls and open cotyledons when grown in the dark, resembling the previously characterized constitutively photomorphogenic mutants (cop, det, fus, and shy). Further analysis of the bim mutants should help define whether plant-derived iGluR agonists target glutamate receptor signaling pathways in plants.

Glutamate Receptor Subtypes Evidenced by Differences in Desensitization and Dependence on theGLR3.3andGLR3.4Genes

“…A second study provided more evidence of a connection between GLR function and light-controlled hypocotyl growth (Brenner et al, 2000). It had been previously established that light-induced membrane depolarizations in hypocotyls Cosgrove, 1989, 1992;Cho and Spalding, 1996;Parks et al, 1998) resembled amino acid-induced depolarizations in root cells (Dennison and Spalding, 2000;Qi et al, 2006).…”

Systems approach identifies an organic nitrogen-responsive gene network that is regulated by the master clock control gene CCA1

“…Wild type A. thaliana Columbia-0 strain was used in all experiments unless indicated otherwise. Seeds were sterilized as described (34) and sown onto basal MS salts (custom-made; GIBCO) with 0.5% (wt/vol) sucrose, 0.8% BactoAgar, and 1 mM KNO3. After 14 days under long-day (16/8-h light/ dark) conditions at 22°C, plants were treated for 2 h in the light at the start of their light cycle by transferring them to basal medium with 0.5% sucrose and a combination of inorganic N sources (20 mM KNO3 and 20 mM NH4NO3) with or without 1 mM MSX (M-5379; Sigma), 10 mM Glu (G-1501; Sigma), and/or 10 mM Gln (G-3126; Sigma).…”

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

“…At low concentrations (50 mM), BMAA induces hypocotyl elongation that is two to three times longer than that in untreated plants when grown in the light. At higher concentrations BMAA is inhibitory to root as well as to shoot growth [59]. These effects suggest that glutamate, and/or BMAA, could have a role in signal transduction in Arabidopsis [56,59].…”

“…At higher concentrations BMAA is inhibitory to root as well as to shoot growth [59]. These effects suggest that glutamate, and/or BMAA, could have a role in signal transduction in Arabidopsis [56,59]. Isolated Arabidopsis mutants resistant to the effects of BMAA might identify the endogenous components of a BMAAtargeted pathway in Arabidopsis [59].…”

“…These effects suggest that glutamate, and/or BMAA, could have a role in signal transduction in Arabidopsis [56,59]. 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].…”