AtGAT1, a High Affinity Transporter for γ-Aminobutyric Acid in Arabidopsis thaliana

Abstract

Functional characterization of Arabidopsis thaliana GAT1 in heterologous expression systems, i.e. Saccharomyces cerevisiae and Xenopus laevis oocytes, revealed that AtGAT1 (At1g08230) codes for an H ؉ -driven, high affinity ␥-aminobutyric acid (GABA) transporter. In addition to GABA, other -aminofatty acids and butylamine are recognized. In contrast to the most closely related proteins of the proline transporter family, proline and glycine betaine are not transported by AtGAT1. AtGAT1 does not share sequence similarity with any of the non-plant GABA transporters described so far, and analyses of substrate selectivity and kinetic properties showed that AtGAT1-mediated transport is similar but distinct from that of mammalian, bacterial, and S. cerevisiae GABA transporters. Consistent with a role in GABA uptake into cells, transient expression of AtGAT1/green fluorescent protein fusion proteins in tobacco protoplasts revealed localization at the plasma membrane. In planta, AtGAT1 expression was highest in flowers and under conditions of elevated GABA concentrations such as wounding or senescence. ␥-Aminobutyric acid (GABA)3 is a four-carbon non-protein amino acid present in prokaryotes and eukaryotes. Although GABA was discovered in 1949 as a constituent of potato tubers, research on GABA metabolism and transport advanced much faster in the animal system as GABA turned out to be the most abundant inhibitory neurotransmitter in the central nervous system (1). Uptake of GABA into neurons and glia has been investigated in detail and shown to be mediated by Na ϩ -dependent and Cl Ϫ -facilitated GABA transporters (GATs), thus regulating concentration and duration of the neurotransmitter GABA in the synapse (2, 3). In addition to its function as a neurotransmitter, GABA plays a role in the development of the nervous system, influencing proliferation, migration, and differentiation (4). With the exception of the general amino acid permease Bra RI from Rhizobium leguminosarum, which belongs to the ATP binding cassette (ABC) transporters, GABA uptake in Gram-negative and Gram-positive bacteria as well as in Saccharomyces cerevisiae is mediated by members of the APC (amino acid/polyamine/organocation) superfamily of transporters (5, 6). In both bacteria and yeast, GABA uptake and biosynthesis are mainly involved in nitrogen and carbon metabolism (7-9), although other functions such as GABA synthesis for pH regulation in Escherichia coli and for normal oxidative stress tolerance in S. cerevisiae have also been postulated (10, 11).Much less is known about the role of GABA and its transport across the plasma membrane in plants. GABA rapidly accumulates under various stress conditions such as low temperature, mechanical stimulation, and oxygen deficiency (12, 13). As in other organisms, GABA is synthesized in plants primarily by decarboxylation of glutamate and degraded via succinic semialdehyde to succinate, a pathway that is also called the GABA shunt (12). Alternatively, succinic semialdehyde can be further catabolized to ␥-h...

A petunia ABC protein controls strigolactone-dependent symbiotic signalling and branching

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“…Transient transformation of Arabidopsis Col-0 protoplasts was performed as described previously 32 . Arabidopsis plants were stably transformed as described previously 38 .…”

The Arabidopsis her1 mutant implicates GABA in E‐2‐hexenal responsiveness

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Alteration of plant primary metabolism in response to insect herbivory

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