Characterization and developmental expression of a glutamate decarboxylase from maritime pine

Abstract

Glutamate decarboxylase (GAD, EC 4.1.1.15) is a key enzyme in the synthesis of γ-aminobutyric acid (GABA) in higher plants. A complete cDNA encoding glutamate decarboxylase (GAD, EC 4.1.1.15) was characterized from Pinus pinaster Ait, and its expression pattern was studied to gain insight into the role of GAD in the differentiation of the vascular system. Pine GAD contained a C-terminal region with conserved residues and a predicted secondary structure similar to the calmodulin (CaM)-binding domains of angiosperm GADs. The enzyme was able to bind to a bovine CaM-agarose column and GAD activity was higher at acidic pH, suggesting that the pine GAD can be regulated in vivo by Ca(2+)/CaM and pH. A polyclonal antiserum was prepared against the pine protein. GAD expression was studied at activity, protein, and mRNA level and was compared with the expression of other genes during the differentiation of the hypocotyl and induction of reaction wood. In seedling organs, GABA levels closely matched GAD expression, with high levels in the root and during lignification of the hypocotyl. GAD expression was also induced in response to the production of compression wood and its expression matched the pattern of other genes involved in ethylene and 2-oxoglutarate synthesis. The results suggest of a role of GAD in hypocotyl and stem development in pine.

Accumulating mechanism of γ‐aminobutyric acid in soybean (Glycine max L.) during germination

“…Plant tissues contain GABA ranging from 0.03 to 2.00 lmol g À1 , and the content increased under different stimuli such as hypoxia, hydraulic pressure, salt stress, temperature shocking, germination and other biotic stress (Molina-Rueda et al, 2010;Shelp et al, 2012;Yang et al, 2015). In leguminous plants, GABA is mainly metabolized via a short pathway called GABA shunt, whereby glutamate is converted to succinate.…”

Identification of two CiGADs from Caragana intermedia and their transcriptional responses to abiotic stresses and exogenous abscisic acid

“…4A). The expression patterns indicated that CiGAD2 might participate in vascular differentiation, like PpGAD in maritime pine (Molina-Rueda et al, 2010). Molina-Rueda et al (2015) also reported that vascular development was closely linked to GABA production corresponding to PpGAD expression.…”

“…Genes encoding GAD enzymes have been successfully identified in many herbaceous plants such as rice (Akama et al, 2001), Arabidopsis (Bouché et al, 2004), maize (Zhuang et al, 2010), and Panax ginseng (Lee et al, 2010) and in some woody plants, such as pine (Molina-Rueda et al, 2010), apple (Trobacher et al, 2013), citrus (Liu et al, 2014), and tea (Mei et al, 2016). Bioinformatics analyses and experimental characterizations have shown that plant GADs contain a calmodulin (CaM)-binding domain that is generally responsible for the cytosolic decarboxylation of glutamate to GABA (Shelp et al, 2012a), although one functional OsGAD 2 without a Ca 2+ /calmodulin domain has been isolated from rice (Akama et al, 2001).…”

“…In citrus, CsGAD1 is predominantly expressed in flowers but CsGAD2 is predominantly expressed in fruit (Liu et al, 2014). Interestingly PpGAD expression was shown to be correlated with vascular differentiation in pine seedlings (Molina-Rueda et al, 2010). Additionally, environmental stimuli were shown to induce the expression of ZmGAD1 in maize (Zhuang et al, 2010) and PgGAD in P. ginseng (Lee et al, 2010).…”

Apparent coordination of isocitrate dehydrogenase and glutamate decarboxylase expression in early stages of tree development

“…GABA is produced by the action of glutamate decarboxylase (GAD), a cytosolic enzyme that is regulated by Ca2+/calmodulin and pH. In contrast to IDH, that it is encoded by just one gene in most of plant genomes [2], GAD is encoded by a small family of nuclear genes [3]. The expression of IDH and GAD has been investigated during the differentiation of hypocotyl and stem in tree species.…”