Calmodulin-dependent and calmodulin-independent glutamate decarboxylases in apple fruit

BMC Plant Biology

Research Article

Christopher P Trobacher¹  Gale G Bozzo¹  Barry J Shelp¹  Adel Zarei¹  Shawn M Clark¹  Jingyun Liu¹ 

[1] Department of Plant Agriculture, University of Guelph, N1G 2W1, Guelph, ON, Canada;

关键词: Abiotic stress;    Apple fruit;    Biochemical regulation;    Calmodulin;    Controlled atmosphere storage;    γ-Aminobutyrate;    Glutamate decarboxylase;    Recombinant protein;   

DOI  :  10.1186/1471-2229-13-144

 received in 2013-07-08, accepted in 2013-09-24,  发布年份 2013

来源: Springer

【 摘 要 】

BackgroundThe ubiquitous, non-proteinaceous amino acid GABA (γ-aminobutyrate) accumulates in plants subjected to abiotic stresses such as chilling, O2 deficiency and elevated CO2. Recent evidence indicates that controlled atmosphere storage causes the accumulation of GABA in apple (Malus x domestica Borkh.) fruit, and now there is increasing interest in the biochemical mechanisms responsible for this phenomenon. Here, we investigated whether this phenomenon could be mediated via Ca2+/calmodulin (CaM) activation of glutamate decarboxylase (GAD) activity.ResultsGAD activity in cell-free extracts of apple fruit was stimulated by Ca2+/CaM at physiological pH, but not at the acidic pH optimum. Based on bioinformatics analysis of the apple genome, three apple GAD genes were identified and their expression determined in various apple organs, including fruit. Like recombinant Arabidopsis GAD1, the activity and spectral properties of recombinant MdGAD1 and MdGAD2 were regulated by Ca2+/CaM at physiological pH and both enzymes possessed a highly conserved CaM-binding domain that was autoinhibitory. In contrast, the activity and spectral properties of recombinant MdGAD3 were not affected by Ca2+/CaM and they were much less sensitive to pH than MdGAD1, MdGAD2 and Arabidopsis GAD1; furthermore, the C-terminal region neither bound CaM nor functioned as an autoinhibitory domain.ConclusionsPlant GADs typically differ from microbial and animal GAD enzymes in possessing a C-terminal 30–50 amino acid residue CaM-binding domain. To date, rice GAD2 is the only exception to this generalization; notably, the C-terminal region of this enzyme still functions as an autoinhibitory domain. In the present study, apple fruit were found to contain two CaM-dependent GADs, as well as a novel CaM-independent GAD that does not possess a C-terminal autoinhibitory domain.

【 授权许可】

Unknown   
© Trobacher et al.; licensee BioMed Central Ltd. 2013. This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.