|Van Berkum, Peter|
Submitted to: Molecular Biology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2001
Publication Date: N/A
Interpretive Summary: It has been known for nearly 45 years that the non-protein amino acid g-aminobutyric acid (GABA) accumulates in plant tissues upon exposure to a variety of stresses. However, the function of GABA accumulation in higher plants has not been well established. In animals, GABA functions as a regulator of neural signal transmission across the small gaps between adjacent neurons, called synapses that contain receptor molecules. We demonstrated by comparing evolutionary patterns of genes that the plant Arabidopsis has genes that code for GABA-receptor-like molecules. This finding is evidence that GABA functions as a signaling molecule in higher plants. This information is useful to scientists because elucidation of the components in the GABA-mediated signaling pathway will provide a complete understanding of the role(s) and function(s) of GABA in higher plants, especially upon the crop plant's exposure to a variety of biotic or abiotic stimuli including mechanical manipulation, cold-shock, heat-shock, drought, salinity, gravity, or pathogens. Results from this study could aid in the development of novel agricultural strategies to improve agricultural productivity and crop quality. In addition, a greater understanding of the factors that control and/or regulate plant GABA-receptor-like molecules could provide insight into mechanism that might control animal GABA-Rs that have been implicated in a host of human diseases and disorders.
Technical Abstract: Animal ionotropic glutamate receptors (iGLRs) and members of subfamily C, or IV, of the G-protein-coupled receptors (subC-GPCRs), which contains the metabotropic glutamate (mGLRs) and g-aminobutyric acidB (GABA-BRs) receptors, have distinct pharmacological and structural characteristics. Likeness among members of the two superfamilies has been noted in the literature. The iGLRs share sequence similarity with regions of the mGLRs and mGLRs share sequence similarity with GABA-BRs. In addition, all of the receptors, iGLRs, mGLRs, and GABA-BRs, have sequence similarities with portions of the bacterial periplasmic binding proteins. An evolutionary link between the iGLRs and the periplasmic binding proteins has been demonstrated via a newly identified family of genes encoding for putative GLRs in plants. Despite the noted similarities among the iGLRs and members of subC-GPCRs, namely the mGLRS or GABA-BRs, there are no data to support an evolutionary link between any member of the two superfamilies, including between members of the mGLRs and iGLRs. We provide evidence for a link between the iGLRs and members of subC-GPCRs by incongruence length difference, parsimony and bootstrap analyses. We demonstrate that the N-terminal regions of the putative GLRs from plants are related to members of subC-GPCRs and that the C-terminal regions of the putative GLRs from plants are related to iGLRs. From this discordant relationship we conclude that the ancestors of the plant GLRs may be the evolutionary progenitors to members of both superfamilies of highly specialized animal receptors via distinct evolutionary mechanisms. A model outlining the evolution of the receptors is presented.