The Arabidopsis thaliana Glutamate-like Receptor Family (AtGLR) - Communication in Plants: Neuronal Aspects of Plant Life - page 197

AtGLR 2.1 and AtGLR 3.5 were downregulated. At GLR1.3 and AtGLR 1.1
seemed not to respond at all to this stress hormone despite the latter being
implicated in the regulation of ABA biosynthesis and antiAtGLR1.1 plants
exhibiting elevated ABA levels (Kang and Turano 2003; Sect. 3.3). Maathuis
et al. (2003) demonstrated that members of the AtGLR family showed time-
dependent changes in transcription in response to Ca 2+ deprivation and

excess Na + ,butnotK + deprivation, supporting the prediction that they

function as NSCCs.
AnalysisofGUSexpressionundercontrolofthe AtGLR3.4 promoter sug-
gested that At GLR3.4 expression was induced by mechanical stress such as
wounding or touch and cold (Meyerhoff et al. 2005). The upregulation of
AtGLR3.4 transcription by wounding and during senescence could suggest
an involvement of methyljasmonate (Sect. 13.3.1), a common component
of both processes (Devoto and Turner 2005). Quantitative RT-PCR analyses
of At GLR3.4 expression revealed that cold-induced transcription was fast,
reaching peak transcript levels after 30 min. Additionally, La 3+ inhibited
cold-induced AtGLR3.4 transcription, suggesting the involvement of Ca 2+ .
AtGLR1.2 and AtGLR2.5 are also upregulated by cold treatment (Zimmer-
mann et al. 2004).

13.4
Conclusions and Future Perspectives

Research into the glutamate receptor-like family has been hindered by the
lack of phenotypes associated with the At GLR genes. The novel pore region
of the predicted proteins and the paucity of understanding of NSCC func-
tion in vivo have made it difficult to predict function. However there are
now several phenotypes associated with At GLR overexpression (Kim et al.
2001) and knockout (Kang and Turano 2003; Kang et al. 2004), and system-
atic electrophysiological characterisation of single At GLR knockout plants
is underway (Qi et al. 2004, 2005; Gilliham 2005). Despite recent progress,
several fundamental questions still remain regarding At GLR function.

13.4.1
Expression

One promising approach to predicting At GLR function is the study of
At GLR gene expression in response to developmental and environmental
cues. In particular, very rapid changes in gene expression in response to en-
vironmental signals (such as application of a ligand, or stresses) implicate
the gene product in specific responses to stimuli (Meyerhoff et al. 2004,