Overexpression of the AtGluR2 Gene Encoding anArabidopsis Homolog of Mammalian Glutamate Receptors Impairs CalciumUtilization and Sensitivity to Ionic Stress in TransgenicPlants

Abstract

We have identified a homolog of the mammalian ionotropic glutamate receptor genes in Arabidopsis thaliana (AtGluR2). This gene was found to alter Ca2+ utilization when overexpressed in A. thaliana. These transgenic plants displayed symptoms of Ca2+ deficiency, including browning and death of the shoot apex, necrosis of leaf tips, and deformation of leaves. Supplementation with Ca2+ alleviated these phenotypes. Overall levels of Ca2+ in tissues of control plants were not significantly different from those of transgenic plants, suggesting that overexpression of the AtGluR2 gene did not affect Ca2+ uptake. However, the relative growth yield as a function of Ca2+ levels revealed that the critical deficiency content of Ca2+ in transgenic plants was three times higher than that of control plants. The transgenic plants also exhibited hypersensitivity to Na+ and K+ ionic stresses. The ion hypersensitivity was ameliorated by supplementation with Ca2+. The results showed that overexpression of the AtGluR2 gene caused reduced efficiency of Ca2+ utilization in the transgenic plants. The promoter of the AtGluR2 gene was active in vascular tissues, particularly in cells adjacent to the conducting vessels. This suggests that AtGluR2 encodes a functional channel that unloads Ca2+ from the xylem vessels. The results together suggest that appropriate expression of the AtGluR2 protein may play critical roles in Ca2+ nutrition by controlling the ion allocation among different Ca2+ sinks both during normal development and during adaptation to ionic stresses.

Detection of a Gravitropism Phenotype inglutamate receptor-like 3.3Mutants ofArabidopsis thalianaUsing Machine Vision and Computation

“…The first studies explored the structure and evolution of the plant gene family (Turano et al 2001;Chiu et al 2002). Subsequent studies employing antisense methods to reduce expression and constitutive promoters to overexpress GLR family members indicated possible roles in coordinating carbon and nitrogen metabolism (Kang and Turano 2003), abscisic acid biosynthesis and signaling (Kang et al 2004), Ca 21 and Na 1 homeostasis (Kim et al 2001), Ca 21 and fungal disease progression (Kang et al 2006), and Ca 21 -mediated stomatal closure (Cho et al 2009). Transcription of multiple family members in the same cell type made heteromeric channels seem probable in planta (Roy et al 2008).…”

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

“…These roles include regulation of hypocotyl elongation (Lam et al, 1998;Dubos et al, 2003), sensing of mineral nutrient status (Kim et al, 2001), regulating carbon/nitrogen balance (Kang and Turano, 2003), resisting aluminum toxicity (Sivaguru et al, 2003) and cold (Meyerhoff et al, 2005), root meristem function (Li et al, 2006;Walch-Liu et al, 2006), as well as jasmonate-mediated defense mechanisms (Kang et al, 2006).…”

Overexpression of the tomato glutamate receptor-like genes SlGLR1.1 and SlGLR3.5 hinders Ca2+ utilization and promotes hypersensitivity to Na+ and K+ stresses

“…ese morphological characteristics of the transgenic plants resembled symptoms of Ca 2+ de ciency observed in transgenic Arabidopsis overexpressing Arabidopsis glutamate receptor (AtGluR2) (Kim et al 2001) and the RsGluR (Kang et al 2006). …”

“…Possible alternative roles for the AtGLR genes were proposed independently by a transgenic plant study and a physiological study. Overexpression of AtGluR2 in Arabidopsis caused symptoms of Ca 2+ de ciency and sensitivity to other ions that could be rescued by providing external Ca 2+ , suggesting that AtGluR2 may function in calcium translocation in plants (Kim et al 2001). Ectopic expression of AtGLR3.1 causes impairment of Ca 2+ oscillation-induced stomatal closure, suggesting a role for AtGLR3.1 in Ca 2+ signaling in guard cells (Cho et al 2009).…”

“…Furthermore, Kim et al (2001) . Transgenic plants did not display hypersensitivity to mannitol, suggesting that the phenotypes observed for K + and Na + are not caused by general osmotic stress (Fig.…”