Overexpression of the AtGluR2 gene encoding an Arabidopsis homolog of mammalian glutamate receptors impairs calcium utilization and sensitivity to ionic stress in transgenic plants.
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.
Kim
S A
SA
Division of Molecular and Life Sciences, Pohang University of Science and Technology, Hyoja Dong, Pohang, Kyungbuk 790-784, Republic of Korea.
Kwak
J M
JM
Jae
S K
SK
Wang
M H
MH
Nam
H G
HG
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D010641:Phenotype; D018520:Plant Shoots / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D011188:Potassium / Q000009:adverse effects; D018091:Receptors, AMPA / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D017470:Receptors, Glutamate / Q000235:genetics* / Q000378:metabolism; D012965:Sodium Chloride / Q000009:adverse effects
D018091:Receptors, AMPA; D017470:Receptors, Glutamate; D012965:Sodium Chloride; C104722:glutamate receptor ionotropic, AMPA 2; D011188:Potassium; D002118:Calcium