DhAR04, an amino acid biosynthetic gene, is stimulated by high salinity in Deharyomyces hansenii

The highly halotolerant yeast Debaryomyces hansenii when grown in the presence of 2M NaCI, increased the expression of AR04 which is involved in the biosynthesis of aromatic amino acids. The function of the isolated gene was verified by complementation of a Saccharomyces cerevisiae null mutant, aro4 Delta , restoring the specific activity of the enzyme (a 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase) to wild-type levels. DhARO4 transcript expression under high salinity was stimulated at the beginning of the exponential growth phase. As the DhARO4 promoter region presents putative GCRE and CRE sequences, its expression was evaluated under conditions of NaCI stress and amino acid starvation, showing similar expression levels for either condition. The combined effect of both stressors resulted in a further increase in transcript levels over the singly added stressors, indicating independent stimulatory events. Our results support the hypothesis that high salinity and amino acid availability are physiologically interconnected.