Investigating glutamate receptor‐like gene co‐expression in Arabidopsis thaliana

Abstract

There is increasing evidence of the important roles of glutamate receptors (GLRs) in plant development and in adaptation to stresses. However, the studies of these putative ion channels, both in planta and in Xenopus oocytes, may have been limited by our lack of knowledge of possible GLR heteromer formation in plants. We have developed a modification of the single-cell sampling technique to investigate GLR co-expression, and thus potential heteromer formation, in single cells of Arabidopsis thaliana leaves. MicroEXpression amplification (MEX) has allowed us to amplify gene transcripts from a single cell, enabling expression of up to 100 gene transcripts to be assayed. We measured, on average, the transcripts of five to six different AtGLRs in a single cell. However, no consistent patterns of co-expression or cell-type-specific expression were detected, except that cells sampled from the same plant showed similar expression profiles. The only discernible feature was the detection of AtGLR3.7 in every cell examined, an observation supported by GUS staining patterns in plants stably expressing promoter::uidA fusions. In addition, we found AtGLR3.7 expression in oocytes induces a Ba 2+ -, Ca 2+ -and Na + -permeable plasma membrane conductance.

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

“…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). While each study provides clues, a consistent theme has not emerged.…”

Cell-specific compartmentation of mineral nutrients is an essential mechanism for optimal plant productivity— another role forTPC1?

“…25 The expression of GLRs in epidermal and mesophyll cells was previously investigated in Arabidopsis and despite a preference of expression of 5-6 members per cell-type, all members lacked both discernible co-expression partner(s) and cell-specificity, with GLR3.7 being the only one found in all cells. 26 Therefore, GLR3.7 is likely to form a plasma membrane localized Ca 2+ -channel in all cell types of the leaf. Our data also shows no difference in CNGC2 expression between cell-types and this data agrees with early studies that suggest that the Ca 2+ -conductance properties across the plasma membrane are equal in all leaf cell-types.…”

Interacting Glutamate Receptor-Like Proteins in Phloem Regulate Lateral Root Initiation in Arabidopsis

“…According to promoter strength and mRNA analyses, at least five of the seven genes comprising the clade to which GLR3.4 belongs are expressed at much higher levels in roots than shoots (Chiu et al, 2002;Roy et al, 2008). This localization information was refined by visualizing the localizations of GLR3.2, GLR3.3, and GLR3.4 fused to GFP, each fusion being expressed in the respective glr knockout mutant and under the control of its native promoter.…”

“…In the years since GLUTAMATE RECEPTOR-LIKE (GLR) genes were discovered in plants (Lam et al, 1998;Lacombe et al, 2001), research has focused on their phylogeny and evolution (Chiu et al, 1999(Chiu et al, , 2002Turano et al, 2001), expression patterns and transcriptional responses (Meyerhoff et al, 2005;Roy et al, 2008), roles in carbon:nitrogen balance (Kang and Turano, 2003), abscisic acid sensing (Kang et al, 2004), and contributions to ionic relations, including Ca 2+ signaling (Kim et al, 2001;Qi et al, 2006;Stephens et al, 2008;Cho et al, 2009). The last category relates closely to the presumed molecular function of GLRs because the homologous ionotropic Glu receptors (iGluRs) in animals combine as heterotetramers to form amino acid-gated ion channels with varying permeability to Na + , K + , and Ca 2+ (Traynelis et al, 2010).…”