AUTHOR=Márquez Dariel , Escalera-Fanjul Ximena , el Hafidi Mohammed , Aguirre-López Beatriz , Riego-Ruiz Lina , González Alicia 

TITLE=Alanine Represses γ-Aminobutyric Acid Utilization and Induces Alanine Transaminase Required for Mitochondrial Function in Saccharomyces cerevisiae

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.695382

DOI=10.3389/fmicb.2021.695382

ISSN=1664-302X

ABSTRACT=<p>The γ-aminobutyric acid (GABA) shunt constitutes a conserved metabolic route generating nicotinamide adenine dinucleotide phosphate (NADPH) and regulating stress response in most organisms. Here we show that in the presence of GABA, <italic>Saccharomyces cerevisiae</italic> produces glutamate and alanine through the irreversible action of Uga1 transaminase. Alanine induces expression of alanine transaminase (<italic>ALT1</italic>) gene. In an <italic>alt1</italic>Δ mutant grown on GABA, alanine accumulation leads to repression of the <italic>GAD1</italic>, <italic>UGA1</italic>, and <italic>UGA2</italic> genes, involved in the GABA shunt, which could result in growth impairment. Induced <italic>ALT1</italic> expression and negative modulation of the GABA shunt by alanine constitute a novel regulatory circuit controlling both alanine biosynthesis and catabolism. Consistent with this, the GABA shunt and the production of NADPH are repressed in a wild-type strain grown in alanine, as compared to those detected in the wild-type strain grown on GABA. We also show that heat shock induces alanine biosynthesis and <italic>ALT1</italic>, <italic>UGA1</italic>, <italic>UGA2</italic>, and <italic>GAD1</italic> gene expression, whereas an <italic>uga1</italic>Δ mutant shows heat sensitivity and reduced NADPH pools, as compared with those observed in the wild-type strain. Additionally, an <italic>alt1</italic>Δ mutant shows an unexpected alanine-independent phenotype, displaying null expression of mitochondrial <italic>COX2</italic>, <italic>COX3</italic>, and <italic>ATP6</italic> genes and a notable decrease in mitochondrial/nuclear DNA ratio, as compared to a wild-type strain, which results in a petite phenotype. Our results uncover a new negative role of alanine in stress defense, repressing the transcription of the GABA shunt genes, and support a novel Alt1 moonlighting function related to the maintenance of mitochondrial DNA integrity and mitochondrial gene expression.</p>