A mitochondrial GABA permease connects the GABA shunt and the TCA cycle, and is essential for normal carbon metabolism

Authors

  • Simon Michaeli,

    1. Department of Molecular Biology and Ecology of Plants, Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
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  • Aaron Fait,

    1. Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany
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    • Present address: French Associates Institute for Agriculture & Biotechnology of Drylands, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion 84990, Israel.

  • Kelly Lagor,

    1. Department of Biological Sciences, The George Washington University, Washington, DC 20052, USA
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    • Present address: Section of Cell and Developmental Biology, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093–0380, USA.

  • Adriano Nunes-Nesi,

    1. Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany
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  • Nicole Grillich,

    1. Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany
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  • Ayelet Yellin,

    1. Department of Molecular Biology and Ecology of Plants, Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
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  • Dana Bar,

    1. Department of Molecular Biology and Ecology of Plants, Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
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  • Munziba Khan,

    1. Department of Biological Sciences, The George Washington University, Washington, DC 20052, USA
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  • Alisdair R. Fernie,

    1. Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany
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  • Frank J. Turano,

    1. Department of Biological Sciences, The George Washington University, Washington, DC 20052, USA
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    • Present address: Plant Sensory Systems, LLC, 1450 S. Rolling Rd. Maryland Techcenter, Room 2046, Baltimore, MD 21227, USA.

  • Hillel Fromm

    Corresponding author
    1. Department of Molecular Biology and Ecology of Plants, Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
      (fax +972 3 6406816; e-mail Hillelf@post.tau.ac.il).
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(fax +972 3 6406816; e-mail Hillelf@post.tau.ac.il).

Summary

In plants, γ-aminobutyric acid (GABA) accumulates in the cytosol in response to a variety of stresses. GABA is transported into mitochondria, where it is catabolized into TCA cycle or other intermediates. Although there is circumstantial evidence for mitochondrial GABA transporters in eukaryotes, none have yet been identified. Described here is an Arabidopsis protein similar in sequence and topology to unicellular GABA transporters. The expression of this protein complements a GABA-transport-deficient yeast mutant. Thus the protein was termed AtGABP to indicate GABA-permease activity. In vivo localization of GABP fused to GFP and immunobloting of subcellular fractions demonstrate its mitochondrial localization. Direct [3H]GABA uptake measurements into isolated mitochondria revealed impaired uptake into mitochondria of a gabp mutant compared with wild-type (WT) mitochondria, implicating AtGABP as a major mitochondrial GABA carrier. Measurements of CO2 release, derived from radiolabeled substrates in whole seedlings and in isolated mitochondria, demonstrate impaired GABA-derived input into the TCA cycle, and a compensatory increase in TCA cycle activity in gabp mutants. Finally, growth abnormalities of gabp mutants under limited carbon availability on artificial media, and in soil under low light intensity, combined with their metabolite profiles, suggest an important role for AtGABP in primary carbon metabolism and plant growth. Thus, AtGABP-mediated transport of GABA from the cytosol into mitochondria is important to ensure proper GABA-mediated respiration and carbon metabolism. This function is particularly essential for plant growth under conditions of limited carbon.

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