Fast-Growing Saccharomyces cerevisiae Cells with a Constitutive Unfolded Protein Response and Their Potential for Lipidic Molecule Production

• Published in: Applied and environmental microbiology Vol. 88; no. 21; p. e0108322
• Main Authors: Nguyen, Phuong Thi Mai, Ishiwata-Kimata, Yuki, Kimata, Yukio
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 08.11.2022
• Subjects: Basic-Leucine Zipper Transcription Factors - genetics; Basic-Leucine Zipper Transcription Factors - metabolism; Biotechnology; Carotenoids; Carotenoids - metabolism; Endoplasmic reticulum; Fluorescence; Fungi; Gene expression; Genetics and Molecular Biology; Green fluorescent protein; Low concentrations; Metabolic engineering; Progeny; Protein Folding; Proteins; Repressor Proteins - genetics; RNA, Messenger - genetics; Saccharomyces cerevisiae; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; Triglycerides; Triglycerides - metabolism; Tunicamycin; Unfolded Protein Response; Yeast; unfolded protein response; lipid synthesis; stress response; Saccharomyces cerevisiae; endoplasmic reticulum; endoplasmic reticulum stress
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/aem.01083-22

In Saccharomyces cerevisiae cells, dysfunction of the endoplasmic reticulum (ER), so-called ER stress, leads to conversion of mRNA to the spliced form ( i), which is translated into a transcription factor that drastically changes the gene expression profile. This cellular response ultimately enhances ER functions and is named the unfolded protein response (UPR). Artificial evocation of the UPR is therefore anticipated to increase productivity of beneficial materials on and in the ER. However, as demonstrated here, cells constitutively expressing i mRNA ( i cells), which exhibited a strong UPR even under nonstress conditions, grew considerably slowly and frequently yielded fast-growing and low-UPR progeny. Intriguingly, growth of i cells was faster in the presence of weak ER stress that was induced by low concentrations of the ER stressor tunicamycin or by cellular expression of the ER-located version of green fluorescent protein (GFP). i cells producing ER-localized GFP stably exhibited a strong UPR activity, carried a highly expanded ER, and abundantly produced triglycerides and heterogenous carotenoids. We therefore propose that our findings provide a basis for metabolic engineering to generate cells producing valuable lipidic molecules. The UPR is thought to be a cellular response to cope with the accumulation of unfolded proteins in the ER. In S. cerevisiae cells, the UPR is severely repressed under nonstress conditions. The findings of this study shed light on the physiological significance of the tight regulation of the UPR. Constitutive UPR induction caused considerable growth retardation, which was partly rescued by the induction of weak ER stress. Therefore, we speculate that when the UPR is inappropriately induced in unstressed cells lacking aberrant ER client proteins, the UPR improperly impairs normal cellular functions. Another important point of this study was the generation of S. cerevisiae strains stably exhibiting a strong UPR activity and abundantly producing triglycerides and heterogenous carotenoids. We anticipate that our findings may be applied to produce valuable lipidic molecules using yeast cells as a potential next-generation technique.