Functional analysis and transcriptional regulation of two orthologs of ARO 10 , encoding broad‐substrate‐specificity 2‐oxo‐acid decarboxylases, in the brewing yeast S accharomyces pastorianus CBS 1483

The hybrid genomes of S accharomyces pastorianus consist of subgenomes similar to those of S . cerevisiae and S . eubayanus, and impact of the genome structure on flavour production and its regulation is poorly understood. This study focuses on ARO 10 , a 2‐oxo‐acid decarboxylase involved in production of higher alcohols. In S . pastorianus CBS 1483, four ARO 10 copies were identified, three resembled S . cerevisiae ARO 10 and one S . eubayanus ARO 10 . Substrate specificities of lager strain (Lg)ScAro10 and LgSeubAro10 were compared by individually expressing them in a pdc1Δ‐pdc5Δ‐pdc6Δ‐aro10Δ‐thi3Δ S . cerevisiae strain. Both isoenzymes catalysed decarboxylation of the 2‐oxo‐acids derived from branched‐chain, sulphur‐containing amino acids and preferably phenylpyruvate. Expression of both alleles was induced by phenylalanine, however in contrast to the S . cerevisiae strain, the two genes were not induced by leucine. Additionally, LgSeub ARO 10 showed higher basal expression levels during growth with ammonia. ARO 80 , which encodes ARO 10 transcriptional activator, is located on CHRIV and counts three Sc‐ like and one Seub ‐like copies. Deletion of LgSeub ARO 80 did not affect LgSeub ARO 10 phenylalanine induction, revealing ‘trans’ regulation across the subgenomes. ARO 10 transcript levels showed a poor correlation with decarboxylase activities. These results provide insights into flavour formation in S . pastorianus and illustrate the complexity of functional characterization in aneuploid strains.