Metabolism and Functions of 4-Aminobutyrate (GABA) in Plants

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Entire sets of gene and protein sequences in plants are rapidly becoming available, and there is increasing need to understand protein structure/function and regulation of metabolic pathways. For the past 2.5 decades, my laboratory has developed internationally recognized leadership in the metabolism and function(s) in plants, of the amino acid 4-aminobutyrate (GABA) and the short-chain fatty acid 4-hydroxybutyrate (GHB), which closely resembles GABA. They are endogenous constituents of the mammalian nervous system, wherein GABA plays a role in neural transmission and development, and functions through interactions with specialized receptors, and GHB serves as a neurotransmitter or neuromodulator postulated to act via a GABA receptor or an independent GHB-specific receptor. The physiological roles of GABA and GHB in plants are not yet clear, but evidence suggests that they are linked to stress, signaling and development. It is becoming clear that GABA metabolism interacts with various biochemical processes and that gene-dependent and -independent processes are involved in its regulation. Elucidation of primary stress- and development-specific responses of the GABA pathway and their interplay with the C/N network and various signaling pathways requires time course experiments and simultaneous monitoring of the relevant genes and metabolites in wild-type plants and genetic mutants. Our current research focuses on the model plant Arabidopsis thaliana because of the availability of molecular reagents, as well as apple (Malus x domestica) fruit because they are prone to physiological injury during controlled atmosphere storage, an abiotic stress. We also study rice (Oryza sativa) and tomato (Solanum lycopersicum) for comparative purposes and for commercial interest. Our approach is innovative and integrative, using physiological, biochemical, and biotechnological methods to identify and understand the regulation of genes/proteins and pathways associated with these metabolites. Our results not only advance fundamental knowledge, but also suggest potential strategies for engineering/developing abiotic and biotic stress resistance and developmental changes in important crop plants.