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=Volume 12 - 2021

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=The GABA shunt constitutes a conserved metabolic route generating NADPH and regulating stress response in most organisms. Here we show that in the presence of GABA, S. cerevisiae produces glutamate and alanine through the irreversible action of Uga1 transaminase. Alanine induces expression of alanine transaminase (ALT1) gene. In an alt1Δ mutant grown on GABA, alanine accumulation leads to repression of the GAD1, UGA1 and UGA2 genes, involved in the GABA shunt which could result in growth impairment. Induced ALT1 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 ALT1, UGA1, UGA2, and GAD1 gene expression, while an uga1Δ mutant shows heat sensitivity and reduced NADPH pools, as compared with those observed in the wild type strain. Additionally, an alt1Δ mutant shows an unexpected alanine-independent phenotype, displaying null expression of mitochondrial COX2, COX3 and ATP6 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 mtDNA integrity and mitochondrial gene expression.