Transcriptomic profiling of the yeast Komagataella phaffii in response to environmental alkalinization

BackgroundAdaptation to alkalinization of the medium in fungi involves an extensive remodeling of gene expression. Komagataella phaffii is an ascomycetous yeast that has become an organism widely used for heterologous protein expression. We explore here the transcriptional impact of moderate alkalinization in this yeast, in search of suitable novel promoters able to drive transcription in response to the pH signal.ResultsIn spite of a minor effect on growth, shifting the cultures from pH 5.5 to 8.0 or 8.2 provokes significant changes in the mRNA levels of over 700 genes. Functional categories such as arginine and methionine biosynthesis, non-reductive iron uptake and phosphate metabolism are enriched in induced genes, whereas many genes encoding iron-sulfur proteins or members of the respirasome were repressed. We also show that alkalinization is accompanied by oxidative stress and we propose this circumstance as a common trigger of a subset of the observed changes. PHO89, encoding a Na+/Pi cotransporter, appears among the most potently induced genes by high pH. We demonstrate that this response is mainly based on two calcineurin-dependent response elements located in its promoter, thus indicating that alkalinization triggers a calcium-mediated signal in K. phaffii.ConclusionsThis work defines in K. phaffii a subset of genes and diverse cellular pathways that are altered in response to moderate alkalinization of the medium, thus setting the basis for developing novel pH-controlled systems for heterologous protein expression in this fungus.

Automated summary

In this study, the transcriptional impact of moderate alkalinization on Komagataella phaffii yeast was explored, searching for suitable novel promoters for transcription response to the pH signal. Results showed significant changes in mRNA levels of over 700 genes when cultures shifted from pH 5.5 to 8.0 or 8.2. Alkalinization provoked oxidative stress and induced the expression of Na+/Pi cotransporter PHO89 through a calcium-mediated signal.